Category: Class 9

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 10 Matter Around Us Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 10 Matter Around Us

9th Science Guide Matter Around Us Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
The separation of denser particles from lighter particles done by rotation at high speed is called ………………
(a) Filtration
(b) sedimentation
(c) decantation
(d) centrifugation
Answer:
(d) centrifugaton

Question 2.
Among the following ……………… is a mixture.
(a) Common Salt
(b) Juice
(c) Carbon dioxide
(d) Pure Silver
Answer:
(b) Juice

Question 3.
When we mix a drop of ink in water we get a . ………………
(a) Heterogeneous Mixture
(b) Compound
(c) Homogeneous Mixture
(d) Suspension
Answer:
(c) Homogeneous Mixture

Question 4.
……………….is essential to perform separation by solvent extraction method.
(a) Separating funnel
(b) filter paper
(c) centrifuge machine
(d) sieve
Answer:
(a) Separating funnel

Question 5.
………………… has the same properties throughout the sample.
(a) Pure substance
(b) Mixture
(c) Colloid
(d) Suspension
Answer:
(a) Pure substance

II. State whether true or false. If false, correct the statement.

1. Oil and water are immiscible in each other.
Answer:
True.

2. A compound cannot be broken into simpler substances chemically.
Answer:
False
Correct statement: A compound can be broken into simpler substances chemically.

3. Liquid – liquid colloids are called gels
Answer:
False.
Correct statement: Liquid – solid colloids are called gels.

4. Buttermilk is an example of heterogeneous mixture.
Answer:
True.

5. Aspirin is composed of 60% Carbon, 4.5% Hydrogen and 35.5% Oxygen by mass. Aspirin is a mixture.
Answer:
False.
Correct statement: It is Compound. It is because the components are combined in a fixed ratio by mass.

III. Match the following :

A	B
Element	Settles down on standing
compound	Impure substance
Colloid	Made up of molecules
Suspension	Pure substance
Mixture	Made up of atoms

Answer:

A	B
Element	Pure substance
compound	Made up of atoms
Colloid	Made up of molecules
Suspension	Settles down on standing
Mixture	Impure substance

IV. Fill in the blanks :

1. A …………………. mixture has no distinguishable boundary between its components.
Answer:
Homogeneous

2. An example of a substance that sublimes is…………
Answer:
Dry ice / Solid CO₂ / Camphor

3. Alcohol can be separated from water by ………….
Answer:
Fractional distillation

4. In petroleum refining, the method of separation used is ………….
Answer:
Fractional distillation

5. Chromatography is based on the principle of………….
Answer:
different solubilities

V. Very Short answer :

Question 1.
Differentiate between absorption and adsorption.
Answer:
Absorption

1. Absorption is the process in which the substance is dissolved throughout the bulk of another substance.
2. For example a paper (absorbent) soaks up or absorbs water.

Adsorption

1. Adsorption is the process in which particles of a substance, (it could be gas, liquid or dissolved solid) adhere to a surface of another substance.
2. For example: charcoal adsorbs gases on its surface. Charcoal is called the adsorbent and the gas is called the adsorbate.

Question 2.
Define Sublimation.
Answer:
Certain solids change directly to a gas without passing through the liquid is called sublimation.

Question 3.
A few drops of ‘DettoP when added to water the mixture turns turbid. Why?
Answer:
The Dettol formulation is a stabilised micro-emulsion. It is manufactured using Chloroxylenol 4.8% and the rest made up by pine oil, isopropanol, castor oil, and soap. On dilution with water, the micro-emulsion destabilises releasing the pine oil and castor oil as a visible bloom. That is why the mixture turns turbid.

Question 4.
Name the apparatus that you will use to separate the components of mixtures containing two, i. miscible liquids, ii. immiscible liquids.
Answer:

1. Miscible liquids – Fractional distillation (Fractionating column and Liebig) Condenser
2. Immiscible liquids – Separating funnel

Question 5.
Name the components in each of the following mixtures.

1. Ice cream
2. Lemonade
3. Air
4. Soil

Answer:

1. Ice cream is a mixture of cream, milk, sugar & sometimes egg.
2. Lemonade is a mixture of lemon juice, sugar and water.
3. Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour, and other gases.
4. Soil is a mixture of clay, sand and various salts.

VI. Answer briefly

Question 1.
Which of the following are pure substances?
Ice, Milk, Iron, Hydrochloric acid, Mercury, Brick, and Water.
Answer:
Ice, Iron, Hydrochloric acid, Mercury, and water are pure substances.

Question 2.
Oxygen is very essential for us to live. It forms 21 % of air by volume. Is it an element or a compound?
Answer:
Oxygen is an element.

Question 3.
You have just won a medal made of 22-carat gold. Have you just procured a pure substance or impure substance?
Answer:
I have procured an impure substance. It is made of 22 parts of pure gold and 2 parts of copper or silver.

Question 4.
How will you separate a mixture containing sawdust, naphthalene and iron filings?
Answer:
The iron filings in the mixture can be separated by Magnetic separation and Naphthalene by sublimation. Sawdust will be remaining at the bottom.

Question 5.
How are homogenous solutions different from a heterogeneous solutions? Explain with examples.
Answer:
Homogeneous mixtures

1. Components are uniformly mixed and it will have a single phase,
   Eg: Alloys, salt solution, lemonade, petrol etc.
2. No boundaries of separation between the components. Has a single phase.
3. Components are not visible to the naked eye.
4. They will be in solid, liquid or in the gaseous phase.

Heterogeneous mixtures

1. Components are not uniformly mixed and it will have more than a single phase. They are called suspensions. Eg: chalk in water, petrol in water, sand in water, etc.
2. There are visible boundaries between the components. Have two or more distinct phases.
3. Components are visible to the naked eye.
4. Can be a solid-liquid or solid-gas or liquid-gas or solid-solid, or liquid-liquid mixtures.

VII. Answer in detail:

Question 1.
Write the differences between elements and compounds and give an example for each.
Elements

1. Contains only one kind of atoms.
2. It is a pure substance.
3. Cannot be broken down further into to simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Copper (Cu), Silicon (Si), Gold (Ag)

Compounds

1. Contains more than one kind of atoms.
2. It is not a pure substance.
3. Can be broken down further into simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Water (H₂0), Carbon dioxide (CO₂), Ammonia (NH₃)

Question 2.
Explain the Tyndall effect and Brownian movement with a suitable diagram.
Answer:
Brownian Movement:
Brownian movement is a kinetic property. When colloidal solutions are viewed under a powerful microscope,it can be seen that colloidal particles are moving constantly and rapidly in zig-zag directions.

The Brownian movement of particles is due to the unbalanced bombardment of the particles by the molecules of the dispersion medium.

Tyndall effect:

• Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution, the path of the beam becomes visible.
• This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone.
• This phenomenon is not observed in case of true solution.
  
• This phenomenon is due to scattering of light by colloidal particles.

Question 3.
How is a mixture of common salt, oil, and water separated? You can use a combination
of different methods.
Answer:

• The mixture is taken in a separating funnel., whose mouth is kept closed.
• Oil and water are immiscible liquids.
• As common salt can dissolve in water it settles as a separate layer at the bottom of the oil layer in the separating funnel.
• Place a beaker below the funnel to collect salt solution.
• Open the tap. Allow the salt solution alone to collect in the beaker.
• From the salt solution, common salt is obtained from evaporation.

Intext Activities

ACTIVITY – 1

1. Is air a pure substance or Mixture? Justify
2. You must have seen brass statues in museums and places of worship. Brass is an alloy made up of approx. 30% zinc and 70% copper. Is Brass a pure substance or a mixture or compound?
Answer:
1. Air is a mixture.
Reason: Air contains nitrogen, oxygen, carbon dioxide, dust particles, water vapour. The composition of air is not the same at all places.
2. Brass is a mixture of solid in solid.

ACTIVITY – 3

Take some powdered iron filings and mix them with sulphur.
i. Divide the mixture into two equal halves.
ii. Keep the first half of the mixture as it is, but heat the second half of the mixture.
iii. On heating you will get a black brittle compound.

Solution:

• When Iron fillings and sulphur are mixed both retain their properties it means they have not undergone any chemical reaction.
  Iron + Sulphur → dirty yellow powder
• When Iron fillings and sulphur are mixed and heated, they undergo a chemical reaction and form Iron sulphide
  
• The black brittle compound is iron sulphate.

ACTIVITY – 4

Identify whether the given substance is a mixture or compound and justify your answer.
1. Sand and water, 2.Sand and iron filings, 3.Concrete, 4. Water and oil, 5. Salad, 6. Water 7. Carbon dioxide, 8. Cement, 9. Alcohol.
Solution :

Substance	Mixture/ compound
1. Sand and water	Mixture – No chemical alteration of two components.
2. Sand and iron filings	Mixture – Sand (silicon and oxygen) is a compound, but sand with iron filings form a mixture.
3. Concrete	Mixture – Concrete is a mixture of lime, cement, water, sand, and other rocks.
4. Water and oil	Mixture – Water is a compound, but when water is mixed with oil, it forms a heterogeneous mixture.
5. Salad	Mixture – salad consists of two or more substances mixed together without any chemical bond.
6. Water	Compound – (2-H and 1-O) Both combining elements are mixed chemically.
7. Carbon dioxide	Compound – (1-C and 2-O) Both combining elements are mixed chemically.
8. Cement	Mixture – Cement is a mixture of many compounds.
9. Alcohol	Compound – It is an organic compound in which one the hydroxyl group is bound to a saturated/unsaturated carbon atom.

ACTIVITY – 5

1. Take bottles containing sugar, starch, and wheat flour.
2. Add one teaspoon full of each one to a glass of water and stir well. Leave it aside for about ten minutes.
What do you observe?
Answer:

When one teaspoon full of sugar, starch and wheat flour are added to a glass of water, sugar dissolves in water but wheat flour does not. If we leave it aside for about 10 minutes, wheat flour settles at the bottom

Test Yourself :

Question 1.
Why whole milk is white?
Answer:
Milk is white because it reflects all wavelengths of visible light. The mixture of reflected colors produces white light. The reason for this is due to the chemical composition of milk and the size of the particles contained within it.

Question 2.
Why the ocean is blue?
Answer:
The ocean looks blue because red, orange, and yellow (long-wavelength light) are absorbed more strongly by water than is blue (short-wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue.

Question 3.
Why the sun looks yellow when it is really not?
Answer:
Our sun is actually white (a mixture of all wavelength of visible spectrum) if we see it from outer space or high-altitude airplanes. Our atmosphere scatters shorter to bigger wavelengths color from sunlight when the white light travels through it. During day, it scatters violet and blue colours leaving yellowish sunlight (the reason why sky is blue and sunlight is yellow). During morning and evening, the sun appears reddish because light rays needs to travel longer distance in atmosphere which causes scattering of yellow light too.

9th Science Guide Matter Around Us Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Liquids have
(a) definite volume, definite shape and are not compressible.
(b) definite volume, no definite shape and are highly compressible.
(c) no definite volume, no definite shape, and slightly compressible
Answer:
(b) definite volume, no definite shape, and slightly compressible

Question 2.
Intermolecular space is maximum in
(a) solids
(b) liquids
(c) gases
(d) all the above
Answer:
(c) gases

Question 3.
Air is a/an,
(a) compound
(b) element
(c) Mixture
(d) Molecule
Answer:
(c) Mixture

Question 4.
Which statement is not correct for a mixture
(a) Components retain their properties
(b) Properties of a mixture are different from its components
(c) Components are mixed in any ratio
(d) Components are separated using simple methods
Answer:
(b) Properties of a mixture are different from its components

Question 5.
A homogeneous mixture of two or more substances is called
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) None of the above.
Answer:
(a) True solution

Question 6.
A colloidal solution is a
(a) Homogeneous mixture
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes
(c) Heterogeneous mixture in which dissolved particles can be seen with naked eyes
(d) All the above
Answer:
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes

Question 7.
Muddy water is an example of
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(b) Suspension

Question 8.
The solution of soap in water is
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(c) Colloidal solution

Question 9.
Water is a/an
(a) element
(b) Mixture
(c) Molecule
(d) compound
Answer:
(d) compound

Question 10.
When two or more elements combine together they form
(a) element
(b) compound
(c) Mixture
(d) Molecule
Answer:
(b) compound

Question 11.
Which of the following will show the “Tyndall Effect”?
(a) Salt solution
(b) Milk & starch solution
(c) Copper sulphate solution
(d) Sugar solution
Answer:
(b) Milk & starch solution

Question 12.
Solid is an arrangement of particles
(a) close together
(b) far together
(c) far apart
(d) none of these
Answer:
(a) close together

Question 13.
The movement of particles in liquids is …………………..
(a) Vibrate on the spot
(b) around each other
(c) Move quicks in all direction
(d) none of these
Answer:
(b) around each other

Question 14.
Gases change to liquid by the process of . …………………..
(a) Melting
(b) Vapourising
(c) Condensing
(d) Freezing
Answer:
(c) Condensing

Question 15.
The physical state of water at 373 K is …………………..
(a) solid
(b) liquid
(c) vapour
(d) plasma
Answer:
(c) vapour

Question 16.
The constituents that form a mixture are also called …………………..
(a) Elements
(b) Compounds
(c) Alloys
(d) Components
Answer:
(d) Components

II. True or False? If false, correct the statement:

1. Atoms are the tiny particles which repel each other when they are squeezed very close.
Answer:
True

2. A teabag placed in a cup of hot water will diffuse into the water.
Answer:
True

3. Evaporation does form bubbles.
Answer:
False
Correct statement: No does not, only boiling forms bubbles.

4. The energy for the process of sublimation can be derived either from the surroundings or from the heat supplied.
Answer:
True

5. The pressure of gases does not depend on the temperature of the gas and the volume it occupies
Answer:
False
Correct statement: The pressure of gases does depend on the temperature of the gas and the volume it occupies

6. Higher the temperature, higher the kinetic energy of particles.
Answer:
True

7. Solids do not flow.
Answer:
True

8. Gases do not diffuse very easily.
Answer:
False.
Correct statement: Gases diffuse very easily.

9. Mixtures are impure substances.
Answer:
True.

10. Salt solution is an example of a heterogeneous mixture.
Answer:
False.
Correct statement: The salt solution is an example of a homogeneous mixture.

III. Match the following :

1. (i)

Column A	Column B
1. Metal	(a) can be compressed easily
2. Metalloid	(b) have the least density
3.Heating curve	(c) Copper, Mercury, Gold, Chromium
4. Gases	(d) Boron, Germanium, Silicon, Arsenic
5. Liquids	(e) a plot of temperature versus time

Answer:
1) – c, 2) – d, 3) – e, 4) – a, 5) – b

(ii)

Column A	Column B
1. Colloidal solution	(a) Carbon, Oxygen, Chlorine, Neon
2. Homogeneous	(b) C12H22O11
3. Cane sugar	(c) dispersed phase, dispersed medium
4. Non-Metals	(d) Oil shaken in the water
5. Suspensions	(e) True solutions

Answer:
1) – c, 2) – e, 3) – b, 4) – a, 5) – d

2. Match the following.

Dispersed phase & Medium	Examples
1. Solid solid	(a) gel
2. Liquid solid	(b) emulsion
3. Liquid-liquid	(c) solid foam
4. Gas solid	(d)alloys

Answer:
1 – d, 2 – a, 3 – b, 4 – c.

3. Match the following.

Dispersed phase & Medium	Examples
1. Solid-liquid	(a) Aerosol
2. Solid gas	(b) Foam
3. Liquid gas	(c) Sol
4. Gas-liquid	(d) Aerosol

Answer:
1 – c, 2 – a, 3 – d, 4 – b.

IV. Fill in the blanks :

1. A substance must absorb …………….. so that it can melt.
Answer:
heat energy

2. Boiling refers to the process by which a substance changes from the liquid to the gaseous state at its …………. point.
Answer:
boiling

3. ………………… is used for industrial refrigeration and transporting frozen food.
Answer:
Dry ice

4. ……………….. is the SI unit of temperature
Answer:
Kelvin

5. Elements contain the …………………of the same kind
Answer:
atoms

6. When elements are physically mixed they form…………………
Answer:
mixtures

7. A compound has a definite …………………
Answer:
formula

8. Mixture of iron filings and salt is a …………………type of mixtures.
Answer:
heterogeneous

9. …………………is the major difference between true solutions, suspensions and colloids.
Answer:
Particle size

10. Phenomenon of Evaporation takes place at the …………………of a liquid.
Answer:
Surface

11. Inverse of sublimation is called …………………
Answer:
deposition

12. Expand LPG …………………
Answer:
Liquefied Petroleum Gas

13. LPG is ………………… gas.
Answer:
inflammable hydrocarbon

14. Compressibility of solids: …………………..
Answer:
can’t be compressed

15. Fluidity of solids: …………….
Answer:
do not flow

16. A mixture does not have fixed …………………….
Answer:
boiling point (or) melting point

17. A compound has a fixed ………………….
Answer:
boiling point (or) melting point

18. The mixture of Iron filling and sale is …………………
Answer:
heterogeneous

19. Gas-solid is ……………………
Answer:
Solid foam

20. Examples of foam is ……………
Answer:
Soap lather / Aerated water

21. Evaporation is always accompanied by…………..in temperature.
Answer:
decrease / cooling effect

V. Very short answer:

Question 1.
Define ‘matter’.
Answer:
The matter is anything that has mass & occupies space.

Question 2.
What are the three states of matter?
Answer:
Solids, liquids, and gases are the three states of matter.

Question 3.
What is an atom?
Answer:
The smallest unit of an element which may or may not have an independent existence but always take part in a chemical reaction is called an atom.

Question 4.
What is a molecule?
Answer:
The smallest unit of a pure substance which always exist independently and can retain physical and chemical properties of that substance is called a molecule.

Question 5.
Give an example for a molecule.
Answer:
Hydrogen molecule – consists of 2 atoms of hydrogens.

Question 6.
How is matter classified?
Answer:
Matter is classified as pure and impure substances.

Question 7.
How are pure substances classified?
Answer:
Pure substances are classified as elements and compounds.

Question 8.
Give examples of pure substances.
Answer:
Copper, oxygen, hydrogen.

Question 9.
How are impure substances classified?
Answer:
Impure substances are classified as homogeneous and heterogeneous.

Question 10.
How are elements classified?
Answer:
Elements are classified as metals, non-metals, and metalloids.

Question 11.
Give examples for metalloids.
Answer:
Boron, silicon, germanium, and arsenic.

Question 12.
Give the chemical formula for cane sugar.
Answer:
C₁₂H₂₂O₁₁

Question 13.
Expand LPG.
Answer:
Liquefied petroleum gas.

Question 14.
Name the element which is used in toothpaste to strengthen our teeth.
Answer:
Fluorine.

Question 15.
Name the compounds used in fertilizers.
Answer:
Compounds of phosphorus, nitrogen, and potassium are used in fertilizers.

Question 16.
Is blood a pure substance?
Answer:
No blood is not a pure substance. It is a mixture of components such as platelets, red and white blood corpuscles, and plasma.

Question 17.
Name the two types of mixtures.
Answer:
Homogeneous and heterogeneous.

Question 18.
Name some substances that sublime.
Answer:
Camphor, Naphthalene, Mothballs.

Question 19.
Name a suitable method used to separate two immiscible liquids.
Answer:
Separating funnel.

Question 20.
Name a method used to separate two miscible liquids.
Answer:
Fractional distillation.

Question 21.
Name the machine used in the centrifugation process.
Answer:
Centrifuge.

Question 22.
Give an example for liquid in gas.
Answer:
Aerosol.

Question 23.
What is “Brownian motion”?
Answer:
The erratic random movement of microscopic particles in a fluid, as a result of ‘ continuous bombardment from molecules of the surrounding medium was discovered by the scientist Robert Brown and so the movement is called “Brownian motion”

VI. Short answer :

Question 1.
What is an element? ’
Answer:
Each element is made up of only one kind of atom. Element is the building block of all materials. The element of any substance cannot be broken down further into simple substances.

Question 2.
What is a compound?
Answer:
When 2 or more elements combine chemically to form a new substance, the new ‘ substance is called a compound.
Example: H₂O.

Question 3.
What is a mixture?
Answer:
A mixture is an impure substance which contains 2 or more kinds of elements or ‘ compounds or both physically mixed together in any ratio.

Question 4.
What is LPG?
Answer:
LPG is liquefied petroleum gas. It contains a mixture of butane and propane gas.

Question 5.
Distinguish an element and a compound.
Answer:
Element:

1. Made up of only one kind of atom.
2. The smallest particle that retains all its properties in the atom cannot be broken down into simpler substances.

Compound:

1. Made up of more than one kind of atom.
2. The smallest particle that retains all the properties in the molecule can be broken down into elements by chemical methods.

Question 6.
Define sublimation.
Answer:
Certain solid substances when heated change directly from solid to gaseous state without attaining liquid state. The vapours when cooled give back the solid substance. This process is known as sublimation.

Question 7.
What is centrifugation?
Answer:
Centrifugation is the process by which fine insoluble solids from a solid liquid mixture can be separated in a machine called a centrifuge.

Question 8.
What is solvent extraction?
Answer:
Solvent extraction method is used to separate two immiscible liquids. This method works on the principle of difference in solubility of two immiscible liquids in a suitable solvent.

Question 9.
What is distillation?
Answer:
Distillation is the process of obtaining pure liquid from a solution. It is actually a combination of evaporation and condensation.

Question 10.
What is fractional distillation?
Answer:
Fractional distillation is used to separate two or more miscible liquids that do not differ much in their boiling points, (less than 25K).

Question 11.
What is chromatography?
Answer:
Chromatography is a separation technique. It is used to separate different components of a mixture based on their different solubilities in the same solvent.

Question 12.
What is paper chromatography?
Answer:
Paper chromatography is used .to separate the different coloured dyes in a sample. It is based on the principle of different solubility in the solvent which is absorbed to different extents by the chromatography paper.

Question 13.
What is a solution?
Answer:
A solution is a homogeneous mixture of two or more substances.

Question 14.
What is a solute?
Answer:
In a solution, the component present in a lesser amount by weight is solute.

Question 15.
What is the solvent?
Answer:
In a solution, the component present in a larger amount by weight is solvent.

Question 16.
What are Colloidal Solutions?
Answer:
A colloidal solution is a heterogeneous system consisting of the dispersed phase and the
dispersion medium.

Dispersed phase

1. Component present in smaller proportion
2. Analogous to solute of a true solution

Dispersion medium

1. Component present in larger proportion
2. Analogous to solvent of a true solution

Question 17.
What is Tyndall effect?
Answer:
Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution the path of the beam becomes visible. This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone. This phenomenon is not observed in case of true solution.

Question 18.
What are the Types of emulsions?
Answer:
The two liquids mixed can form different types of emulsions. For example, oil and water can form an oil in water emulsion, where the oil droplets are dispersed in water, or they can form a water in oil emulsion, with water dispersed in oil.

Question 19.
What are the uses of emulsions?
Answer:
Emulsions find wide applications in food processing, pharmaceuticals, metallurgy, and many other important industries.

VII. Answer in detail :

Question 1.
What are the characteristics of Pure Substances? (or) List out the characteristics of Pure Substances.
Answer:

• Made up of only one kind of atom or molecule.
• The ratio of the components of a pure substance is fixed.
• Have a characteristic set of properties. Physical properties like boiling point, melting point, density etc. are
• fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Has the same composition throughout i.e it is homogenous in nature

Question 2.
List out the characteristics of Mixtures.
Answer:

• The constituents of a mixture are loosely held together without any chemical force between the constituents and in such a case the constituents retain their individual properties.
• A mixture can be prepared by mixing the constituents in any proportion i.e mixtures do not have any fixed amount of constituents Formation of mixtures does not involve any exchange of energy.
• Mixtures do not have any characteristic set of properties. Physical properties of mixtures like boiling point, melting point, etc. are not fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Components of a mixture can be separated by physical methods.

Question 3.
Tabulate Differences between mixtures and compounds.
Answer:
Mixtures

1. A mixture can be separated into its constituents by physical processes like filtration, evaporation, sublimation, magnet distillation, solvent extraction.
2. A mixture retains or shows the properties of its constituents
3. Energy (in the form of heat light etc.) is neither given out nor absorbed in the preparation of a mixture
4. The composition or proportion is variable a mixture does not have a definite formula
5. A mixture does not have a fixed boiling point or melting point

Compounds :

1. A compound cannot be separated into its constituents by physical processes but can be only separated by a chemical process
2. The properties of a compound are entirely different from those of its constituent elements
3. Energy (in the forth of heat, light etc.) is given out or absorbed during the preparation of a compound
4. The composition of a compound is fixed. The constituents are present in a fixed ratio by mass. The compound has a definite formula.
5. A compound has a fixed boiling point or melting point

Question 4.
Write the Classification of colloids based on physical state of dispersed phase and dispersion medium.
Answer:
Dispersed phase or the dispersion medium can be a solid, or liquid or gas. There are eight different combinations possible (The combination in which both the dispersed phase and dispersion medium are gases does not exist as gases are completely miscible and can never give rise to a colloidal solution).

Question 5.
Two immiscible liquids are taken in the above funnel for separation.
Which is denser, X or Y? Suggest any one example for X and one for Y. A third liquid Z which is soluble only in Y is added to the mixture and contents in the funnel are shaken well. How many layers will you observe now? How will you separate the three liquids? Boiling point of X is 98°C, that of Y is 43°C and that of Z is 75°C.
Answer:
Boiling point of the 3 liquids are given as
X is 98°C – Which corresponds to water.
Y is 43°C – Which corresponds to oil.
Z is 75°C – Which corresponds to alcohol.
‘Y’ is more denser.
Only two layers are observed. X is separated by separating funnel, Z is separated by distillation method. Y – is in the distillation flask.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 8 Sound Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 8 Sound

9th Science Guide Sound Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following vibrates when a musical note is produced by the cymbals in a orchestra?
(a) stretched strings
(b) stretched membranes
(c) air columns
(d) metal plates
Answer:
(d) metal plates

Question 2.
Sound travels in air:
(a) if there is no moisture in the atmosphere.
(b) if particles of medium travel from one place to another.
(c) if both particles as well as disturbance move from one place to another.
(d) if disturbance moves.
Answer:
(d) if disturbance moves

Question 3.
A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through
(a) wax
(b) vacuum
(c) water
(d) empty vessel
Answer:
(b) vacuum

Question 4.
The maximum speed of vibrations which produces audible sound will be in
(a) seawater
(b) ground glass
(c) dry air
(d) Human blood
Answer:
(b) ground glass

Question 5.
The sound waves travel faster
(a) in liquids
(b) in gases
(c) in solids
(d) in vacuum
Answer:
(c) in solids

II. Fill in the blanks.

1. Sound is a ……………….wave and needs a material medium to travel.
Answer:
longitudinal mechanical

2. Number of vibrations produced in one second is………………..
Answer:
Frequency

3. The velocity of sound in solid is …………… than the velocity of sound in air.
Answer:
greater

4. Vibration of object produces ……………..
Answer:
Sound

5. Loudness is proportional to the square of the ……………………
Answer:
Amplitude of vibration of sound

6. …………..is a medical instrument used for listening to sounds produced in the body.
Answer:
Stethoscope

7. The repeated reflection that results in persistence of sound is called ……………………
Answer:
Reverberation

III. Match the following :

1. Tuning fork	a. The point where density of air is maximum.
2. Sound	b. Maximum displacement from the equilibrium position.
3. Compressions	c. The sound whose frequency is greater than 20,000 Hz
4. Amplitude	d. Longitudinal wave
5. Ultrasonics	e. Production of sound

Answer:
1 – e, 2 – d, 3 – a, 4 – b, 5 – c

IV. Answer in brief :

Question 1.
Through which medium sound travels faster, iron or water? Give reason.
Answer:
Sound travels faster through iron than water.
Reason: The speed of sound depends on the nature of the medium. As Iron is a solid, sound travels faster through iron than Water.

Question 2.
Name the physical quantity whose SI unit is ‘hertz’. Define.
Answer:
The SI unit of frequency is Hertz. Frequency is the number of waves produced in one second.

Question 3.
What is meant by supersonic speed?
Answer:
Supersonic speed is the speed of an object that exceeds the speed of sound in air (330 ms^-1).

Question 4.
How does the sound produced by a vibrating object in a medium reach your ears?
Answer:

• When an object vibrates, it sets the particles of the medium around it vibrating.
• The vibrating particles in the medium displace from the equilibrium position and exerts pressure on adjacent particles.
• Thus this process continues in the medium till the sound reaches our ear.

Question 5.
You and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
We cannot hear any sound on the moon.
Reason: Absence of atmosphere (medium) in the moon.

V. Answer in detail :

Question 1.
Describe with a diagram, how compressions and rarefactions are produced.
Answer:
Compressions :
When a vibrating body moves forward, it creates a region of high pressure is known as compressions. In compression, the particles are denser. Compressions are the region where particles are crowded together.

Rarefaction :
When the vibrating body moves backward, it creates a region of low pressure (i.e) low density of particles. This is called rarefaction. Rarefactions are the regions where particles are spread apart.

Question 2.
Verify experimentally the reflection of the laws of sound.
Answer:

• Make two identical long pipes using chart paper.
• Arrange them on a table near wall.
• Keep a clock near the open end of one pipe and hear the sound of the clock through the other pipe.
• Adjust the pipe till the sound of the clock heard with more clarity.
• Now measure the angle of incidence and reflection and see the relationship between the angles.
• The angle in which the sound is incident is equal to the angle in which sound is reflected.
• Direction of incident sound, direction of the reflected and the normal are in the same plane.
• Thus laws of reflection of sound are verified.

Question 3.
List the applications of sound.
Answer:
Applications of ultrasound

• Ultrasound can be used in cleaning technology. Minute foreign particles can be removed from objects placed in a liquid bath through which ultrasound is passed.
• Ultrasounds can also be use d to detect cracks and flaws in metal blocks.
• Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
• Ultrasound may be employed to break small ‘stones’ formed in the kidney into fine grains. These grains later get flushed out with urine.

Question 4.
Explain how do SONAR works?
Answer:
SONAR stands for Sound Navigation And Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction, and speed of underwater objects. Sonar consists of Science – 9 (Physics)
a transmitter and a detector and is installed at the bottom of boats and ships. The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector.

The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarines, icebergs etc.

VI. Numerical problems :

Question 1.
The frequency of a source of sound is 600 Hz. Calculate the number of times it vibrates in a minute?
Solution :
Given :
Frequency, v = 600 Hz.
Frequency = Number of vibrations in a second.
Frequency in a minute = Fequency per second × 60
= 600 Hz × 60
No. of vibrations in a minute = 36,000 Hz (or) 36 kHz.

Question 2,.
A stone is dropped from the top of a tower 750 m high into a pond of water at the base of the tower. Calculate the number of seconds for the splash to be heard? (Given g = 10 ms^-2 and speed of sound = 340 m s^-1)
Solution :
Given :
Height of tower, s = 750 m
Acceleration, g =10 ms^-2
Speed of sound, v – 340 ms^-1
Initial velocity of stone, u =0 (stone at rest)

Consider
(i) Time taken to reach the pond, t₁
(ii) Time taken by sound to reach top, t₂
According to Equation of Motion, s = ut + \(\frac{1}{2}\) at²
Here, s = ut₁ + \(\frac{1}{2}\) gt₁²
Substituting the values, 750 = 0 × t₁ + \(\frac{1}{2}\) × 10 × t₁²
750 = 5 t₁²
t₁² = 150
t₁ = 12.25 s
Time taken by sound to reach top t₂ = \(\frac{s}{v}=\frac{750}{340}\) = 2.2s
t₂ = 2.2 s
Time for splash to be heard at top, t = t₁ + t₂
t = 12.25 + 2.2
t = 14.45 s
Time for splash to be heard at top, t = 14.45 s.

Intext Activities

ACTIVITY – 1

Take a tuning fork and strike its prongs on a rubber pad. Bring it near your ear. Do you hear any sound? Now touch the tuning fork with your finger. What do you feel? Do you feel vibrations?

Aim :
To demonstrate the vibration of a molecule.
Materials Required : 1. Tuning fork, 2. Rubber band.

Procedure:

1. Take a tuning fork and strike its prongs on a rubber pad.
2. Bring it near your ear. Hear the sound.
3. Touch the tuning fork with finger.
4. Try to feel the vibrations.

Observation :
When we strike the tuning fork on the rubber pad, it starts vibrating. The vibrations can be felt.

Conclusion :
The tuning fork vibrates the molecules which will vibrate the nearby molecules.
[Vibration = movement of molecule from mean position],

[End of the activity]

ACTIVITY – 2

Take a coil or spring and move it forward and backward. What do you observe? You can observe that in some parts of the coil the turns will be closer and m some other parts the turns will be far apart.
Sound also travels in a medium in the same manner. We will study this now.

Aim :
To demonstrate the propagation of Longitudinal wave. (Sound)
Materials required : 1. Coil, 2. Spring

Procedure:

1. Take a coil or spring
2. Move it forward and backward.

Observations:

1. Some parts of the coil, the turns are closer.
2. In other parts, the turns are far apart.

Conclusion :

1. Closer turns represent compressions.
2. Far apart turns are rarefactions.
3. Longitudinal waves propagate through compressions and rarefactions.

[End of the activity]

ACTIVITY – 3

Listen to the audio of any musical instruments like flute, nathaswaram, tabla, drums, veena etc., Tabulate the differences between the sounds produced by the various sources.

Aim :
To compare the sounds of musical instruments.
Materials required: 1. Flute, 2. Drums, 3. Veena,

Procedure :

1. Hear the instrumental music of flute, drums and veena.
2. Tabulate the difference between the sounds.

Observation :

Name of musical instrument	Vibrating Part	Characteristics
1. Flute	Air column	Longer wavelength, low-frequency low pitch.
2. Drums	Stretched membrane	Shorter wavelength, high-frequency High pitched
3. Veena	Stretched string

Conclusion :
Sounds in the different music instruments are characterised by the following qualities such as. 1. Amplitude, 2. The wavelength, 3. Frequency, 4. Pitch, 5. Loudness.

9th Science Guide Sound Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Which of the following is a non-mechanical wave?
(a) sound
(b) water
(c) light
(d) none of the above
Answer:
(c) light

Question 2.
Sound cannot travel through …………………
(a) darkness
(b) gases
(b) vacuum
(d) all of these
Answer:
(c) vacuum

Question 3.
In longitudinal waves, the particle vibrates in a ………………….. direction of propagation.
(a) parallel
(b) perpendicular
(c) curved
(d) all of these
Answer:
(b) perpendicular

Question 4.
Human beings cannot hear …………………
(a) infrasonic sound
(b) sonic sound
(c) ultrasonic sound
(d) a & c
Answer:
(d) a & c

Question 5.
The frequency greater than 20,000 Hz is ………………. sound.
(a) infrasonic
(b) ultrasonic
(c) audible
(d) sonic
Answer:
(b) ultrasonic

Question 6.
of sound depends on the amplitude of the wave,
(a) Loudness
(b) Pitch
(c) Timbre
(d) Tone
Answer:
(a) Loudness

Question 7.
………………. is a general term for the distinguishable characteristic of wave
(a) Pitch
(b) Amplitude
(c) Frequency
(d) Timbre
Answer:
(d) Timbre

Question 8.
Sound travels in air as ……………..wave.
(a) longitudinal
(b) transverse
(c) electromagnetic
(d) all of these
Answer:
(a) longitudinal

Question 9.
The distance between two adjacent crest is called …………………..
(a) amplitude
(b) wavelength
(c) time period
(d) frequency
Answer:
(b) wavelength

Question 10.
When temperature increases the speed of sound
(a) increases
(b) decreases
(c) remains same
(d) none of these
Answer:
(a) increases

Question 11.
The relation between speed, frequency and wavelength is ………………


Answer:
(c) V = γλ

Question 12.
SI unit of wavelength is ……………………………..
(a) Hertz
(b) metre per second
(c) decibel
(d) metre
Answer:
(d) metre

Question 13.
The speed of sound in a gaseous medium depends on …………….
(a) pressure
(b) temperature
(c) density
(d) all of these
Answer:
(d) all of these

Question 14.
The elastic property of medium is a factor of …………. medium.
(a) gas
(b) liquid
(c) solid
(d) none of these
Answer:
(c) solid

Question 15.
To hear an echo, the minimum distance of the obstacle from the source of sound must be ………………
(a) 34 m
(b) 17 m
(c) 340 m
(d) 170 m
Answer:
(b) 17 m

Question 16.
The part of ear that turns pressure variations into electrical signals is .
(a) the hammer
(b) anvil
(c) cochlea
(d) stirrup
Answer:
(c) cochlea

Question 17.
The frequency of source of sound is 60 Hz. Then the number of vibrations in a minute will be ………………..
(a) 36
(b) 360
(c) 3600
(d) 6000
Answer:
(c) 3600

Question 18.
Sonar is a device that uses to measure the distance, direction and speed of the underwater objects.
(a) radio waves
(b) infrared waves
(c) water waves
(d) ultrasonic waves
Answer:
(d) ultrasonic waves

Question 19.
The speeds of sound in four different media are given below. Which of the following is the most likely speed in ms-1 with which the two underwater whales in a sea can talk to each other when separated by a large distance?
(a) 5170
(b) 1280
(c) 340
(d) 1530
Answer:
(d) 1530

[Note = Speed of sound in Sea Water is 1530 ms^-1]

II. Fill in the blanks :

1. The propagating disturbance that travels in a medium is called a ………………
Answer:
Wave

2. Rarefactions are the regions of ……………. where particles are spread apart.
Answer:
low pressure

3. Sound travels faster in ……………. and slower in ……………..
Answer:
Solid, Gas

4. The loudness of sound depends on the ……………. of the sound wave.
Answer:
Intensity

5. A sound of single frequency is called …………….and a collection of tones is called .
Answer:
Tone, Note

6. The speed of sound in air at 0°C is ……………..
Answer:
330 ms^-1

7. …………….is an unwanted sound.
Answer:
Noise

8. Loudness equal to (or) greater than …………….can be painful to the ear.
Answer:
120 dB

9. …………….allows bats to navigate through dark caves and find insects for food.
Answer:
Echolocation

10. …………….is an image obtained by the use of reflected ultrasonic waves.
Answer:
An echogram

11. Depth of an ocean can be determined by …………….
Answer:
SONAR

12. The distance of underwater objects can be deduced by the formula …………….
Answer:
Id = v x t

13. …………….muscle contracts in response to electrical depolarisation of the muscle cells.
Answer:
Cardiac

14. Velocity of sound by a tuning fork frequency of 480 Hz is 340 ms Its wavelength is …………….
Answer:
0.7 m

15. The part of ear that collects the sound from the surroundings is . …………….
Answer:
Pinna

16. Ultrasounds can also be used to detect cracks and flaws in …………….
Answer:
Metal blocks

17. In the inner ear, the pressure variations are turned into electrical signals by the …………….
Answer:
Cochlea

III. Match the following :

I.

1. Stethoscope	a) Repeated reflections
2. Echogram	b) Multiple reflections
3. SONAR	c) Ultrasonic waves
4. Reverberation	d) Speed of underwater objects

Answer:
1-b, 2-c,3-d,4-a

II.

1.  Wave	a) Unwanted sound
2. Sound	b) Successive reflections
3. Noise	c) Movement of disturbance
4. Thunder	d) Mechanical wave

Answer:
1-c, 2-d, 3 -a, 4-b

III.

1. Cochlea	a) Amplification of vibrations
2. Pinna	b) Electrical signals to the brain
3. Ear bones	c) Pressure variations to an electrical signal
4. Auditory nerve	d) Collection of sound

Answer:
1-c, 2-d,3 -a,4-b

IV. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both Assertion and Reason are true and Reason is the correct explanation of
Assertion. .
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion : Human beings Cannot hear infrasonic sound.
Reason : Sound with frequency less than 20 Hz is called infrasonic sound.
Answer:
(a) Both Assertion and Reason are true and Reason . is the correct explanation of Assertion

Question 2.
Assertion : As the amplitude of sound increases, the loudness of sound decreases.
Reason : The loudness of sound depends on the amplitude of the wave.
Answer:
(d) Assertion is false but reason is true
Correct Assertion : As the amplitude of sound decreases, the loudness of sound decreases.

Question 3.
Assertion : The sound of thunder is heard a little latter than the flash of light.
Reason : The speed of sound is much less than the speed of light.
Answer:
(a) Both Assertion and reason are true and Reason is the correct explanation of Assertion

Question 4.
Assertion : The speed of sound in air is less than speed of sound in solid.
Reason : If we increase the temperature of medium, the speed of sound increases in any medium.
Answer:
(b) Both assertion and reason are true but reason is not the correct explanation of assertion
Reason : The particles in sound are closer in solids than air.

Question 5.
Assertion : The sound which we hear again is called Echo.
Reason : The sensation of sound (Echo) persists in our brain for about 1 s.
Answer:
(c) Assertion is true but reason is false
Reason : The sensation of sound persists in our brain for about 0 – 1 s.

V. State whether true or false. If false, correct the statement:

1. Vibrating particles travel all the way from vibrating object to ear. ,
Answer:
False.
Correct statement: Vibrating particles do not travel all the way from vibrating object to ear.

2. The small to and fro motion is called vibration.
Answer:
True.

3. Pitch is a general term for the distinguishable characteristic of a tone.
Answer:
false.
Correct statement: Timbre is general term for the distinguishable characteristic of a tone.

4. The speed of sound in a gaseous medium depends on the nature of gas.
Answer:
True.

5. The direction of incident sound, direction of reflected sound and the normal are in different Planes.
Answer:
False.
Correct statement: The direction of incident sound, direction of reflected sound and the normal are in same plane.

6. Ultrasonic sounds cannot be heard by the Human beings.
Answer:
True.

7. The Eardrum moves inward when a rarefaction reaches it.
Answer:
False.
Correct statement: The Eardfum moves outward when a rarefaction reaches it.

VI. Very Short Answer questions :

Question 1.
What is a wave?
Answer:
The disturbance which is carried forward in a medium is called wave.

Question 2.
Distinguish between compression and rarefactions.
Answer:
Compression :
Compressions are the regions where particles are crowded together.

Rarefaction :

Rarefactions are the regions of low pressure where particles are spread apart.

Question 3.
Name the five characteristics of’a sound wave. ‘
Answer:
1. Amplitude, 2. Frequency, 3. Time period, 4. Wavelength, 5. Velocity or speed.

Question 4.
Name the distinguishing factors of sound.
Answer:
1. Loudness, 2. Pitch, 3. Timbre (or) quality.

Question 5.
Define : Intensity.
Answer:
Intensity is defined as the amount of energy per unit time perpendicular to the direction of propagation of the wave.

Question 6.
Differentiate tone from note.
Answer:
Tone : A sound of single frequency
Note : A collection of tones.

Question 7.
What is Reverberation?
Answer:
The repeated reflection that results in persistent sound is called reverberation.

Question 8.
Expand the abbreviation of the term SONAR.
Answer:
SONAR – SOUND NAVIGATION AND RANGING.

Question 9.
What type of waves are illustrated by the movement of a rope whose one end is moved up and down?
Answer:

• The movement of rope whose one end is moved up and down is an example of
  Transverse wave.
• The movement of particles of the medium is perpendicular to the direction of
  propagation of the wave is called Transverse Wave.

Question 10.
Name the type of waves produced when a tuning fork is struck in air.
Answer:
Longitudinal waves are produced when a tuning fork is struck in air.

Question 11.
A stone is dropped on the surface of water in a pond. Name the types of waves produced.
Answer:
Transverse waves are produced when a stone is dropped into the pond.

Question 12.
State one observation from every day life which shows that sound travels much more slower than light.
Answer:
The flash of lightening is seen before we hear the sound of thunderstorm.
Reason : The speed of sound (344 m/s) is less than the speed of light (3 × 10⁸ m/s)

Question 13.
What name is given to those air-crafts which fly at speeds greater than the speed of sound?
Answer:
Supersonic Aircraft.

Question 14.
Name the device which is used to produce sound in laboratory experiments.
Answer:
Tuning fork is used to produce sound in laboratory experiments.

Question 15.
What should an object do to produce sound?
Answer:

• An object should vibrate in a medium.
• Vibrations travel as disturbances to reach our ears as sound.

Question 16.
Can sound travel through vacuum?
Answer:

• Sound cannot travel through vacuum.
• Sound needs a material medium to travel like air, water, steel, etc.

VII. Answer in brief :

Question 1.
How do we hear sound?
Answer:

• Mechanical energy vibrates an object.
• The vibrations reach our ear and we hear sound.

Question 2.
Why are sound waves called mechanical waves?
Answer:
Sound waves are called as mechanical waves because sound waves need a medium to propagate and propagation through medium due to interaction of the particles.

Question 3.
Define : (i) Amplitude (ii) Frequency
Answer:
Amplitude (A) : The maximum displacement of the particles of the medium from their original undisturbed position when a wave passes through the medium. Unit: metre (m).
Frequency (n) : The number of vibrations produced in one second is called Frequency of the wave. Unit: Hertz (Hz) or s^-1

Question 4.
Define : Wavelength (λ) and Timbre
Answer:
Wavelength (λ) : The maximum distance in which a sound wave repeats itself (or) In a Sound Wave the distance between the centres of two consecutive compressions (or) two consecutive rarefactions. Unit: metre (m).
Timbre: Timbre is the characteristic which distinguish two sounds of same loudness and pitch of two different instruments.

Question 5.
How are the Wavelength and frequency of a Sound wave related to its speed?
Answer:
Speed (v), Wavelength (λ) and frequency of sound (υ) are related by the following equation: Speed (v) = Wavelength (λ) × Frequency (υ) => v = λ × υ

Question 6.
What are the factors that intensity of Sound depends upon?
Answer:
The intensity of sound depends on the

• Amplitude of the source.
• Distance of the observer from the source.
• Surface area of the source.
• Density of the medium.
• Frequency of the source.

Question 7.
On which factors the speed of sound in gaseous medium depends?
Answer:

• Pressure of the medium.
• Temperature of the medium.
• Density of the medium.
• Nature of the medium.

Question 8.
On which factors the speed of sound in solid medium depends?
Answer:

• Elastic property of the medium.
• Temperature of the medium.
• Density of the medium.

Question 9.
Mention the fequency ranges of infrasoncis and ultrasonics.
Answer:

• Sound waves with frequencies below audible range is termed as Infrasonics.
  Infrasonics: Frequencies less than 20 Hz.
• Sound waves with frequencies above audible range is called as Ultrasonics.
  Ultrasonics: Frequencies greater than 20,000 Hz.

Question 10.
Why is a sound wave called a longitudinal wave?
Answer:
Sound wave is called a Longitudinal wave because

• It produces compressions and rarefactions in the air.
• The particles of air vibrates parallel to the direction of propagation.

Question 11.
Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
The Timbre (or) quality of sound enables us to identify our friend by his voice.

Question 12.
List the causes of noise pollution.
Answer:

• Hearing problems.
• Rupture of eardrum and hearing loss.
• Psychological damages.

Question 13.
Why are roots and walls of the auditorium covered with rough plaster?
Answer:
To reduce the effect of reverberation in large halls of the auditorium.

Question 14.
Give two practical applications of reflection of Sound?
Answer:

• SONAR – Reflection of sound is used to measure the distance, direction and speed of underwater objects.
• Stethoscope – Patient’s heartbeats reach doctor’s ear by multi reflections of sound.

Question 15.
What is acoustics?
Answer:
Acoustics is a branch of physics that deals with the study of properties of Sound.

VIII. Answer in detail :

Question 1.
Prove that sound needs a material medium for its propagation.
Answer:
To prove sound needs a material medium.

• Take an electric bell and an airtight glass jar connected to a vacuum pump.
• Suspend the electric bell inside the airtight jar and press the switch of the bell and hear the sound of the bell.
• Now pump out the air from the glass jar gradually.
• If the jar has vaccum, any sound will not be heard.
• So, sound needs a material medium to travel (here, it is air) and it is proved.

Question 2.
Distinguish between Loudness and Intensity of the Sound?
Answer:
Loudness

1. Loudness is a quantity by virtue of which sound can be distinguished.
2. The loudness of the sound is determined by its amplitude. Loudness a (Amplitude) .

Intensity

1. Intensity of the sound wave is defined as the amount of sound energy passing through unit area per second.
2. The amplitude of sound decides the intensity.

Question 3.
What is an echo? Write the conditions to hear an echo.
Answer:
A repeated sound that is caused by the reflection of sound waves from a surface.

Conditions for echo

• For echo, the time interval between the original sound and reflected sound must be 0.1 s. The sound must go to the obstacle and return to the listener on reflection after 0.1s.
• Total distance covered by the sound from source to the obstacle and reflected to listener must be atleast 340 ms^-1 × 0.1s = 34m.
• So the minimum distance of the obstacle from the source of sound = half of total distance
  \(\frac{34 \mathrm{~m}}{2}\) = 17m.
• This distance will change with the temperature of air.

Question 4.
Explain the working of human ear with diagram.
Answer:
Working of Human Ear
Parts of human ear are (i) outer ear, (ii) middle ear, (iii) inner ear.
(i) Outer ear [Pinna] : It collects the sound from the surroundings and directs towards auditory canal.
(ii) Middle ear : Sound reaches the auditory canal and vibrates the eardrum (or) tympanic membrane, a thin membrane.
Three small bones (hammer, anvil, stirrup) amplify the vibrations, several times. The middle ear transmits the amplified pressure variations to the inner ear.

(iii) Inner ear : (Cochlea) (j) Receives vibrations, (ii) converts them into electrical signals and (iii) they are sent to the Brain thro’ auditory nerve.
The Brain interprets the electrical signals to sound.

IX. Numerical problems :

Question 1.
The frequency of tuning fork is 484 Hz. What is the time period?
Solution :
Frequency of tuning fork, n = 484 Hz.

Question 2.
Velolcity of sound in air is 344 ms^-1 What is the range of wavelength of audible sound?
Solution :
Velocity of sound in air, v = 344 ms^-1
Audible frequency range = 20 – 20,000 Hz
We know V = \(v \lambda \Rightarrow \lambda=\frac{v}{v}\)
When Fequency v = 20Hz
\(\lambda=\frac{344}{20}=17.2 \mathrm{~m}\)
When Frequency, v = 20,000Hz
\(\lambda=\frac{344}{20,000}=0.0172 \mathrm{~m}\)
Range of wavelength of audible Sound = 0.0172 m- 17.2 m

Question 3.
A body vibrates 3000 times in one minute. If the velocity of sound in air 330 ms^-1, find (i) Frequency of vibration (ii) Wavelength.
Solution :
Velocity of sound in air, v = 330 ms^-1
No.of vibrations in a minute = 3000 / minute.
(i) Frequency, (Vibrations produced in one second)

Question 4.
A person is listening to a tone of 400 Hz from a distance of 500 m from the source of sound. What is the time interval between successive compressions from source?
Solution :
Fequency of tone u = 400 Hz.
Time interval between two
successive compressions
from source = Time period of wave.

Time interval between two successive compressions from source = 0.0025 s.

Question 5.
An echo returned in 3s. What is the distance of reflecting surface from the source given that the speed of sound is 330 ms^-1.
Solution :
Speed of sound, v = 330 ms^-1
Time of the echo, t = 3s.
Total distance travelled by the sound 2d = v × t = 330 × 3
2d = 990 m.
2d = Distance from source to reflecting surface + distance from reflecting surface to the listener.
So, distance from the source to reflected surface = \(\frac{\text { Total distance }}{2}\)
= \(\frac{2 d}{2}\)
Distance of the reflecting surface from the source = \(\frac{990}{2}\)
= 495m

Question 6.
Two persons are at opposite ends of a steel rod. One strikes the end of rod with a stone. Find the ratio of time taken by the sound wave in air and in steel to reach the second person. (Sound of speed in steel = 5960 ms^-1, Sound of speed in air = 344 ms^-1)
Solution :
Sound of speed in steel = 5960ms^-1
Sound of speed in air =344ms^-1

Question 7.
A Sound wave travels at a speed of 344 ms^-1. If the wavelength is 1.5 cm, what is the frequency of Wave? Will it be audible?
Solution :
Velocity of soung , v = 344ms^-1
Wavelength of sound. λ = 1.5cm

Audible frequency range = 20 – 20000Hz
So frequency 2,29,333 is not audible.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 5 Magnetism and Electromagnetism Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 5 Magnetism and Electromagnetism

9th Science Guide Magnetism and Electromagnetism Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following converts electrical energy into mechanical energy?
(a) Motor
(b) Battery
(c) Generator
(d) Switch
Answer:
(a) Motor

Question 2.
Transformer works on ………………….
(a) AC only
(b DC only
(c) Both AC and DC
Answer:
(a) AC only

Question 3.
The part of the AC generator that passes the current from the armature coil to theexternal circuit is .
(a) field magnet
(b) split rings
(c) slip rings
(d) brushes
Answer:
d) brushes

Question 4.
The unit of magnetic flux density is
(a) Weber
(b) weber/metre
(c) weber/metre²
(d) weber. metre²
Answer:
(c) weber/metre²

II. Fill in the blanks :

1. The SI Unit of magnetic field induction is ……………..
Answer:
Tesla

2. Devices which is used to convert high alternating current to low alternating current is ………………….
Answer:
transformers

3. An electric motor converts ………………
Answer:
electrical energy into mechanical energy

4. A device for producing electric current is ……………
Answer:
generator

III. Match the following :

1. Magnetic material	a) Oersted
2. Non-magnetic material	b) Iron
3. Current and magnetism	c) Induction
4. Electromagnetic induction	d) Wood
5. Electric generator	e) Faraday

Answer:
1-b, 2-d, 3 -a, 4-e, 5-c

IV. State whether true or false. If false, correct the statement

1. A generator converts mechanical energy into electrical energy.
Answer:
True

2. Magnetic field lines always repel each other and do not intersect.
Answer:
True

3. Fleming’s Left-hand rule is also known as the Dynamo rule.
Answer:
False.
Correct statement: Fleming’s Left-hand rule is also known as the motor rule.

4. The speed of rotation of an electric motor can be increased by decreasing the area of the coil.
Answer:
False.
Correct statement: The speed of rotation of an electric motor can be increased by increasing the area of the coil.

5. A transformer can step up the direct current.
Answer:
False.
Correct statement: A transformer can step up alternating current (AC).

6. In a step-down transformer the number of turns in the primary coil is greater than that of the number of turns in the secondary coil.
Answer:
True.

V. Answer in brief:

Question 1.
State Fleming’s Left Hand Rule.
Answer:
It states that while stretching the three fingers of the left hand in a perpendicular manner with each other if the direction of the current is denoted by the middle finger of the left hand and the second finger is for the direction of the magnetic field then the thumb of the left hand denotes the direction of the force or movement of the conductor.

Question 2.
Define magnetic flux density.
Answer:
The number of magnetic field lines crossing unit area kept normal to the direction of field lines is called magnetic flux density. Its unit is Wb/m²

Question 3.
List the main parts of an electric motor.
Answer:
The main parts of an electric motor are:

1.  Shaft,
2. Primary and Secondary windings,
3. Ball bearings,
4. Armature,
5. Stator,
6. Commutator,
7. Brushes,
8. Terminals

Question 4.
Draw and label the diagram of an AC generator.

PARTS
N, S – Permanent magnet
A B C D – Rectangular coil or armature.
S₁,₂ – Slip rings
B₁, B₂ – Carbon brushes

Question 5.
State the advantages of AC over DC.
Answer:
Advantages of AC over DC:

• • The Voltage of AC can be varied easily using a device called a transformer. The AC can be carried over long distances using step-up transformers. The loss of energy while distributing current in the form of AC is negligible.
  • Direct current cannot be transmitted as such. The AC can be easily converted into DC. Generating AC is easier than DC. The AC can produce electromagnetic induction which is useful in several ways.

Question 6.
Differentiate step up and step down transformer.
Answer:

Step-up transformer	Step down transformer
1. It is a device used to raise the electric voltage (Vs > Vp)	It is designed to reduce the voltage (Vs < Vp).
2. It has more turns on its secondary wind-ing in comparison to the primary one (Ns > Np).	It has fewer turns on the secondary winding (Ns < Np).
3. It is used to start the electrical motor and step-up the windings.	It is used to balance the ratio of voltage and current on the primary and secondary windings.
4. It takes a lot of voltage to initially start the motor turning. It increases the voltage but decreases the current.	The secondary windings have fewer turns which mean low voltage and higher current while it is the opposite in the case of the primary winding.
5. It is found is a television and in power stations.	It is found in laptops and phone chargers.

Question 7.
A portable radio has a built-in transformer so that it can work from the mains instead of batteries. Is this a step up or step down transformer? Give reason.
Answer:
A step-down transformer is used in a portable radio in order to reduce the voltage.

Question 8.
State Faraday’s laws of electromagnetic induction.
Answer:
First law: Whenever there is a change in magnetic flux linked with a coil, an electric current is induced. The induced potential difference lasts so long as there is a change in the magnetic flux linked with the coil.

Second law: The magnitude of the induced current is directly proportional to the rate of change of magnetic flux linked with the coil.

VI. Answer in detail :

Question 1.
Explain the principle, construction, and working of a dc motor.
Answer:
Principle: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming’s left-hand rule.
Construction: An electric motor consists of the following main parts:

Armature: It is a rectangular coil ABCD having a large number of turns of this insulated copper wire wound over a soft iron core. The armature is placed between the poles of the field magnet and it can be rotated about an axis perpendicular to the magnetic field lines.

Split rings (commutators): It consists of a cylindrical metal ring split into two halves S₁ & S₂ As the coil rotates, the split rings also rotate about the same axis of rotation. The function of the split ring is to reverse the direction of current in the coil after every half rotation.

Carbon brushes: Two graphite or flexible metal rods maintain a sliding contact with split rings S₁and S₂ alternately.

Battery: A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings.

Working: A simple coil is placed inside two poles of a magnet. Now, look at the current-carrying conductor segment AB. The direction of the current is towards B, whereas in the conductor segment CD the direction is opposite. As the current is flowing in opposite directions in the segments AB and CD, the direction of the motion of the segments would be in opposite directions according to Fleming’s left-hand rule. When two ends of the coil experience force in opposite direction, they rotate.

If the current flow is along the line ABCD, then the coil will rotate in a clockwise direction first and then in an anticlockwise direction. If we want to make the coil rotate in any one direction, say clockwise, then the direction of the current should be along ABCD in the first half of the rotation and along DCBA in the second half of the rotation.

When the gap in the split ring commutator is aligned with terminals X and Y there is no flow of current in the coil. But, as the coil is moving, it continues to move forward bringing one of the split ring commutators in contact with the carbon brushes X and Y. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil.

Question 2.
Explain two types of transformer.
Answer:
Step-up transformer: The transformer used to change a low alternative voltage to a high alternating voltage is called a step-up transformer, ie (V_s > V_p)
In a step-up transformer, the number of turns in the secondary coil is more than the number of turns in the primary coil (N_s >N_p)

Step down transformer: The transformer used to change a high alternating voltage to a low alternating voltage is called a step-down transformer (V_s< V_p). In a step-down transformer, the number of turns in the secondary coils is less than the number of turns in the primary coil (N_s < N_p)

Question 3.
Draw a neat diagram of an AC generator and explain its working.
Answer:

• An alternating current (AC) generator, as shown in, consists of a rotating rectangular coil ABCD called armature placed between the two poles of a permanent magnet.
• The two ends of this coil are connected to two slip rings S₁ and S₂. The inner sides of these rings are insulated.
• Two conducting stationary brushes B₁and B₂ are kept separately on the rings S₁and S₂ respectively.
• The two rings S₁ and S₂ are internally attached to an axle.
• The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the external circuit.
• When the coil is rotated, the magnetic flux linked with the coil changes. This change in magnetic flux will lead to generation of induced current.
• The direction of the induced current, as given by Fleming’s Right Hand Rule, is along ABCD in the coil and in the outer circuit it flows from B₂ to B₁
• During the second half of rotation, the direction of current is along DCBA in the coil and in the outer circuit it flows from B₁ to B₂.
• As the rotation of the coif continues, the induced current in the external circuit is changing its direction for every half a rotation of the coil.

Intext Activities

ACTIVITY – 1

Put a magnet on a table and place some paper clips nearby. If you push the magnet slowly towards the paper clips, there will be a point at which the paper clips jump across and stick to the magnet. What do you understand from this?

Aim :
To study the property of a magnet.

Materials required :
Strong bar magnet, paper clips.

Procedure: Case (i)

• Put a bar magnet on a table and place some paper clips nearby.
• If you push the magnet slowly towards the paper clips, there will be a point at which the paper clips jump across and stick to the magnet. What do you understand from this?

Conclusion :

•  From the above activity, we can conclude that magnets have an invisible field all around them which attracts magnetic materials.
• In this space we can feel the force of attraction or repulsion due to the magnet.
• Thus magnetic field is the region around the magnet where its magnetic influence
  can be felt. It is called a magnetic field.
  [End of the activity]

ACTIVITY – 2

Take a cardboard and thread a wire perpendicular through it. Connect the wire such that current flows up the wire. Switch on the circuit. Let the current flow. Place a magnetic compass on the cardboard and mark the position. Now move the magnet and mark the new position. If you join all the points you will find that it is a circle. Reverse the direction of the current, you will find the magnetic circles are clockwise.

Aim :
To observe the magnetic field around a straight conductor carrying current.

Materials required :
Thick copper wire (conductor), some connecting wires, battery, key, white cardboard, magnetic compass.

Procedure :

• Fix white cardboard horizontally.
• Make a small hole at its centre.
• Pass the thick copper wire through the hole, perpendicular to the cardboard.
• Join the ends of the thick copper wire to a battery and a key with the help of some connecting wires.
• Switch on the circuit. Let the current flow.
• Place a magnetic compass on the cardboard.
• Mark S and N point of the compass X and Y respectively on the cardboard.
• Move the compass such that S end touches Y.
• Now mark the N end as Z In the next step move the compass such that S end touch Z. Repeat the steps. .
• Now join all the points. What do you observe?
• Now keep the compass away from the centre and follow.

Observation:

• It is seen that it is a circle.
• We can draw another magnetic line and the magnetic lines are concentric circles and also we will find the magnetic lines are anti-clockwise.
• When the direction of current is reversed, the direction of magnetic lines of force
  are clockwise.

[End of the activity]

ACTIVITY – 3

Create your own electromagnet
You are given a long iron nail, insulation coated copper wire, and a battery. Can you make your own electromagnet?

Aim :
To create your own electromagnet.

Materials required :
Iron nail insulated coated copped wire, battery, and paper clips.

Procedure :

• Take an iron nail, wind ten or more loops of insulated copper wire around it. However, make sure not to make the diameter of the loop more than a centimetre in width.
• Connect the ends of the wire to a key and a battery.
• Switch on the key and bring some paper clips close to the nail.
• Switch off the key. What do you observe?

Observation :
When the key is switched on, the electromagnet attracts the paper clips due to the current flowing through the coil wound around the iron nail. When the key is switched off, the paper clips detach from the iron nail

Conclusion:
Thus an electromagnet is a temporary magnet which behaves as a magnet in the presence of an electric current.

9th Science Guide Magnetism and Electromagnetism Additional Important Questions and Answers

Choose the correct answer:

Question 1.
The direction of the magnetic field around a straight conductor carrying current can be determined by …………………
(a) Fleming’s left-hand rule
(b) Lenz’s law
(e) Right-hand thumb rule
(d) Fleming’s right-hand rule
Answer:
(a) Fleming’s left-hand rule

Question 2.
The magnetic field produced due to a circular wire at its centre is _______.
(a) at 45° to the plane of the wire
(b) at 60° to the plane of the wire
(c) in the plane of the wire
(d) perpendicular to the plane of the wire
Answer:
(d) perpendicular to the plane of the wire

Question 3.
A magnetic field exerts no force on ………………
(a) stationary electric charge
(b) a magnet
(e) an electric charge moving perpendicular to its direction
(d) an unmagnetized iron bar.
Answer:
(a) stationary electric charge

Question 4.
At the centre of a magnet, the magnetism is ______ .-
(a) zero
(b) same as the poles
(c) maximum
(d) minimum
Answer:
(a) zero

Question 5.
Induced current flows through a coil ______.
(a) more than the period during which flux changes through it.
(b) less than the period during which flux changes through it
(c) only for the period during which flux changes through it
(d) None of the above
Answer:
c) only for the period during which flux changes through it

Question 6.
Which of the following instruments works by electromagnet-ic induction?
(a) dynamo
(b) moving coil galvanometer
(c) telephone receiver
(d) simple motor
Answer:
(a) dynamo

Question 7.
For making a strong electromagnet the material of the core should be_______.
(a) brass
(b) laminated steel strips
(c) soft iron
(d) steel
Answer:
(c) soft iron

Question 8.
Magnetic field lines determine ______
(a) the shape of the magnetic field
(b) only the direction of the magnetic field
(c) only the relative strength of the magnetic field
(d) both the direction and the relative strength of the magnetic field
Answer:
(d) both the direction and the relative strength of the magnetic field

Question 9.
A magnetic needle is kept in a non-uniform magnetic field. It experiences …………….
(a) a force and a torque
(b) a force but not a torque
(c) a torque but not a force
(d) neither a force nor a torque
Answer:
(a) a force and a torque

Question 10.
The most suitable material for making permanent magnets is ………………..
(a) copper
(b) aluminum
(c) iron
(d) steel
Answer:
(d) steel

Question 11.
An electric generator converts
(a) electrical energy into mechanical energy
(b) mechanical energy into heat energy
(e) electrical energy into electrical energy
(d) mechanical energy into electrical energy
Answer:
(d) mechanical energy into electrical energy

II. Fill in the blanks:

1. The magnetic field inside a _____ is uniform.

Answer:
magnet

2. An AC generator is provided with …………… slip rings which rotate with the coil.
Answer:
two

3. The moving part of an electric motor is called ……………
Answer:
shaft

4. A magnetic field is a ………………….quantity
Answer:
Vector

5. The SI unit of magnetic field strength is ……………………
Answer:
Tesla

6. The laws of induction were given by ________
Answer:
Faraday

7. The relation between weber and Tesla is________
Answer:
1wb = 1T × 1m²

8. Unlike magnetic poles ________whereas like poles ________
Answer:
attract, repel

9. Magnetic lines of force never ______ each other.
Answer:
intersect

10. Sailors use ………………. to find direction in order to navigate on the sea.
Answer:
Magnetic compass

11. The strongest natural magnet is ………………….
Answer:
lodestone magnetite

12. The ______ produces its own magnetic field, which shields the earth’s ozone layer from the …………… and is important in navigation.
Answer:
Earth, solar wind

13. Sea turtles return to their birth beach many decades after they were born due to ……………..
Answer:
geomagnetic imprinting

14. Magnetic field at a point is ………………. to the magnetic field lines.
Answer:
tangential

15. ……………… is the number of magnetic field lines passing through a given area.
Answer:
Magnetic flux

16. The direction of the magnetic lines around a current-carrying conductor can be easily
understood using the ………….. rule.
Answer:
right-hand thumb rule

17. The magnetic field lines are stronger near the ……………… and it diminishes as you go away from it.
Answer:
current-carrying wire

18. A charge moving in a magnetic field, in a direction other than the direction of the magnetic field, experiences a force. It is called the ………………. force.
Answer :
magnetic Lorentz

19. When the conductor is perpendicular to the magnetic field, the force will be the …………….., When it is parallel to the magnetic field, the force will be ………………..
Answer:
maximum, zero

20. An electric bell contains an …………………., consisting of coils of insulated wire wound around
iron rods.
Answer:
electro magnet

21 . No force acts in a current carrying conductor when it is to the magnetic
field.
Answer: parallel

III. Match the following :

Question 1.

1. Electric generator	a) Electro magnetic induction
2. Dynamo	b) Fleming’s left hand rule
3. Magnetic field lines	c) Slip rings
4. Electric motor	d) North to south

.Answer:
1-c, 2 -a, 3-d, 4-b

Question 2.

1. Electricity and magnetism	a) Step-down transformer
2. Force on the conductor	b) Hans Christian Oersted
3. Electric bell	c) I L B
4. Ns <Np	d) Electromagnet

Answer:
1-b, 2-c, 3-d, 4-a

IV. State whether true or false. If false, correct the statement:

1. Fleming’s left-hand rule is also known as the dynamo rule.
Answer:
False.
Correct statement: Fleming’s right-hand rule is also known as the dynamo rule.

2. Magnetic field lines always repel each other and do not intersect.
Answer:
True.

3. A current flowing in a wire gives rise to a magnetic field.
Answer:
True.

4. The magnetic field lines due to a straight wire carrying current are parallel.
Answer:
False.
Correct statement: The magnetic field lines due to a straight wire carrying current are concentric circles.

5. A generator converts mechanical energy into electrical energy.
Answer:
True.

6. The magnetic field is a quantity that has magnitude only.
Answer:
False
Correct statement: The magnetic field is a quantity that has magnitude and direction

7. Magnetic fields do not interact with electric charges in motion.
Answer:
False.
Correct statement: Magnetic fields do not interact with electric charges at rest.

8. The force on a charged particle is moving in a magnetic field is maximum when the angle between the direction of motion and field is 90°.
Answer:
True.

9. An electric motor converts mechanical energy into electrical energy.
Answer:
False.
Correct statement: An electric motor converts electrical energy into mechanical energy.

10. The field at the centre of the long circular coil carrying current will be parallel straight lines.
Answer:
True.

11. A wire with green insulation is usually the live wire of an electric supply.
Answer:
False
Correct statement: A wire with green insulation is usually the earth wire of an electric supply.

12. An electric generator works on the principle of electromagnetic induction.
Answer:
True.

13. Permanent magnets are made of hard magnetic materials like alnico.
Answer:
True.

14. The pole of a freely suspended magnet which points towards the north is called the south pole and what points towards south is celled north pole.
Answer:
False.
Correct statement: The pole of a freely suspended magnet that points towards the north is called the north pole and that points towards the south are called a south pole.

15. The magnetic poles always exist in pairs.
Answer:
True

16. A galvanometer is an instrument that can detect the presence of a current is a circuit.
Answer:
True

V. Assertion and Reason type questions :

Mark the correct choice as:
(a) If both assertion and reason are true and the reason is the correct explanation of assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true

Question 1.
Assertion (A): When 2 long parallel wires, hanging freely are connected in parallel to a battery, they come closer to each other.
Reason (R): Wires carrying current in opposite direction repel each other.
Answer :
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion

Reason: The wires are parallel to each other but the direction of current in it is in the same direction, so they attract each other. If the current in the wire is in opposite direction then wires repel each other.

Question 2.
Assertion (A) : The work done by a magnetic field on moving charge is zero.
Reason (R) : In a magnetic field force is perpendicular to the velocity.
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of

Question 3.
Assertion (A): A current-carrying conductor experiences a force in a magnetic field.
Reason (R): The net charge on a current-carrying conductor is zero.
Answer:
(b) Assertion and reason are true but the reason is not the correct explanation of the assertion

Reason: When a current-carrying conductor having no net charge is placed in a magnetic field, the free electrons of the conductor move towards the positive end of the conductor with the same drift velocity, hence magnetic force acts on them; The positive ions of the conductor being stationary, do not experience any magnetic field.

Question 4.
Assertion (A) : A magnetic field exerts a force on a moving charge in the same direction as the direction of the field itself.
Reason (R) : The direction of force is given by Fleming’s left-hand rule.
Answer :
(d) Assertion is false but the reason is true
Reason: According to Fleming’s left-Hand Rule, the direction of the magnetic force on a moving charge is always perpendicular to the magnetic field.

VI. Define the following :

Question 1.
Define the terms magnet and magnetism.
Answer
The substances which have the property of attracting small pieces of iron, nickel, cobalt, etc, are called magnets, and this property of attraction is called magnetism.

Question 2.
Define natural magnet.
Answer:
It is a piece of lodestone, which is a black iron oxide (Fe₃ O₄) called magnetite. The word lodestone means a leading stone.

Question 3.
Define artificial magnet.
Answer:
Pieces of iron and other magnetic materials which can be made to acquire the properties of natural magnets are called artificial magnets.

Question 4.
Define magnetic field.
Answer:
The region around a magnet within which its influence can be experienced is called a magnetic field.

Question 5.
Define magnetic field lines of force.
Answer:
The path in a magnetic field in which a unit north pole tends to move when allowed to do so is known as magnetic field lines of force.

Question 6.
Define magnetic flux.
Answer:
Magnetic flux is the number of magnetic field lines passing through a given area. It is denoted by (Φ) and its unit is weber (Wb).

Question 7.
Define magnetic shielding.
Answer:
The process of stopping the magnetic field from entering into a region is called magnetic shielding.

Question 8.
Define magnetic effect of electric current.
Answer:
A current-carrying conductor is always associated with a magnetic field around it is called the magnetic effect of current. It was first discovered by Hans Christian Oersted in 1820.

Question 9.
Define the right-hand thumb rule.
Answer:
If the current-carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

Question 10.
Define Fleming’s Left Hand Rule.
Answer:
The law states that while stretching the three fingers of the left hand in a perpendicular manner with each other if the direction of the current is denoted by the middle finger of the left hand and the second finger is for the direction of the magnetic field then the thumb of the left hand denotes the direction of the force or movement of the conductor.

Question 11.
Define electromagnet.
Answer:
lt is a solenoid with a soft iron core placed inside it. When current is passed through the solenoid, the soft iron core becomes a temporary magnet.

Question 12.
Define electric motor.
Answer:
lt is a device to convert electrical energy into mechanical energy. It is based on the principle that when a current-carrying coil is placed in a magnetic field, it experiences a force.

Question 13.
Define electromagnetic induction.
Answer:
Whenever the magnetic lines of force passing through a closed-circuit change, a voltage and hence a current is induced in it. This phenomenon is called electromagnetic r induction. It was discovered by Michael Faraday in 1831.

Question 14.
Define Fleming’s Right Hand Rule.
Answer:
Stretch the thumb, forefinger, and middle finger of your right hand mutually perpendicular to each other. If the fore finger indicates the direction of the magnetic field and the thumb indicates the direction of motion of the conductor, then the middle finger will indicate the direction of the induced current. Fleming’s Right-hand rule is also called the “generator rule”.

Question 15.
Define an electric generator or a dynamo.
Answer:
lt is a device to convert mechanical energy into electrical energy. It is based on the principle of electromagnetic induction that a current is induced in a closed circuit when the magnetic field passing through it changes.

Question 16.
Define a Transformer.
Answer:
The transformer is a device used for converting low voltage into high voltage and high voltage into low voltage. It works on the principle of electromagnetic induction.

Question 17.
Define step up and step down transformer.
Answer:
Step-up transformer: The transformer used to change a low alternating voltage to a high alternating voltage is called a step-up transformer, (ie) (V_s > V_p).
Step down transformer: The transformer used to change a high alternating voltage to a low alternating voltage is called a step-down transformer (V_s < V_p).

VII. Answer in brief :
Question 1.
Mention the properties of magnetic lines of force.
Answer:
Magnetic lines of force are closed continuous curves, extending through the body of the magnet.
Magnetic lines of force start from the North Pole and end at the South Pole.

Question 2.
Give the uses of magnets in everyday life.
Answer:

•  Used in radio and stereo speakers
• Used in almirah and refrigerator doors to snap them closed.
• In medicine, magnetic resonance imaging (MRI) scanners expose the inner parts of the patient’s body for detailed examination by doctors.

Question 3.
Can two magnetic lines of force intersect? Justify your answer:
Answer:
No, if two magnetic lines of force intersect then there will be two tangents and hence two directions of the magnetic field at the point of intersection. This is not possible.

Question 4.
Why does a compass needle get deflected when brought near a bar magnet?
Answer:
The magnetic field of the magnet exerts a force on both the poles of the compass needle. The forces experienced by the two poles are equal and opposite. These two forces form a couple which deflects the compass needle.

Question 5.
Draw magnetic field lines around a bar magnet.
Answer:

Question 6.
Give some uses of electromagnets.
Answer:

• It is used in factories and cranes to lift heavy iron ingots and steel, scraps from one place to another.
• Used in hospitals to remove iron splinters from the eyes of the patients.
• Used in electric bells, relays, electric switches etc.

Question 7.
Two coils A and B of insulated wire are kept close to each other. Coil A is connected to a galvanometer. While coil B is connected to a battery through a key. What would happen if.
(i) a current is passed through coil B by plugging the key?
(ii) the current is stopped by removing the plug from the key?
Answer:
(i) If a current is passed through coil B by plugging the key, the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil – A (As the current in coil B changes, the magnetic field associated with it also changes).

(ii) If the current is stopped by removing the plug from the key :
The needle of the galvanometer in coil – A momentarily moves but to the opposite side. It means that now the current flows in the opposite direction in coil – A.

VIII. Answer in detail

Question 1.
Explain the principle, construction, and working of an AC generator.
Answer:

• An alternating current (AC) generator, consists of a rotating rectangular coil ABCD called armature placed between the two poles of a permanent magnet.
• The two ends of this coil are connected to the two slip rings S₁ and S₂. The inner sides of these rings are insulated.
• Two conducting stationary brushes B₁ and B₂ are kept separately on the rings S₁ and S₂ respectively. The two rings S₁ and S₂ are internally attached to an axle.
• The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two bushes are connected to the external circuit.
  When the coil is rotated, the magnetic flux linked with the coil changes. This change in magnetic flux will lead to generation of induced current.
• The direction of the induced current, as given by Fleming’s Right Hand Rule, is along ABCD in the coil and in the outer circuit it flows from
  B₂ to B₁
• During the second half of rotation, the direction of current is along DCBA in the coil and in the outer circuit it flows from B₁ , to B₂
• As the rotation of the coil continues, the induced current in the external circuit is changing its direction for every half a rotation of the coil.

Question 2.
Explain the working of following devices.
(i) Speaker
(ii) Magnetic levitation trains.
Answer:
(i) Inside the speaker, the electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly in position whereas the electromagnet is mobile. As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is, in turn, attracted to and repelled from the permanent magnet vibrating back and forth. The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air towards our ears.

(ii) Magnetic levitation (Maglev) is a method by which an object is suspended with no support other than magnetic fields. In Maglev trains two sets of magnets are used, one set to repel and push the train up off the track,’ then another set to move the floating train ahead at great speed without friction. In this technology, there is no moving part. The train travels along a guide way of magnets which controls the train’s stability and speed using the basic principles of magnets.

Question 3.
Explain the application of electromagnets in the field of medical system.
Answer:
Nowadays electromagnetic fields play a key role in advanced medical equipment such as hyperthermia treatments for cancer, implants and magnetic resonance imaging (MRI). In a, sophisticated equipments working based on electromagnetism can scan minute details of the human body.

Many of the medical equipments such as scanners, X-ray equipments and other equipments also use principle of electromagnetism for their functioning

Question 4.
Explain the properties of magnetic lines of force.
Answer:

• Magnetic lines of force are closed, continuous curves, extending through the body of the magnet.
• Magnetic lines of force start from the North Pole and end at the South Pole.
• Magnetic lines of force never intersect.
• They will be maximum at the poles than at the equator.
• The tangent drawn at any point on the curved line gives the direction of the magnetic field.

IX. Numerical Problems:

Question 1.
A 0.4 m wire, stretched horizontally, carries an electric current of 15 A, in a magnetic field whose magnetic field intensity is 0.1 N/Am. What is the magnitude on the wire?
Given: l = 0.4 m, I = 15A
Magnetic induction B = 0.1 N/Am
Solution:
Force to be used F = B I l
= 0.1 × 15 × 0.4
F = 0.6N

Question 2.
A wire 10 cm long carrying a current of 1.5 A is held in a uniform magneÑic field in which B = 10^-3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.
Given : Length of the wire l = 10 cm = 0.10 m
Current I= 1.5 A
Magnetic induction B = 10^-3T
Solution:
ForceF = B I l
= 10^-3 × 1.5 × 0.10
= 1.5 × 10^-3 N.

Question 3.
A conductor of length 50 cm carrying a current of 5 A is placed perpendicular to a magnetic field of induction 2×10 ^-3T. Find the force on the conductor.
Solution :
Force on the conductor = ILB
= 5 × 50 × 10^-2 × 2 × 10^-3
= 5 × 10^-3

Question 4.
A current-carrying conductor of a certain length, kept perpendicular to the magnetic field experiences a force F. What will be the force if the current is increased four times, the length is halved and the magnetic field is tripled?
Solution :
F = I L B = (4I) × \(\left(\frac{L}{2}\right)\) × (3 B) =6 F
Therefore, the force increases six times.

Question 5.
The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a 220 V ac supply. What will be the output voltage?
Solution:

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 7 Heat Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 7 Heat

9th Science Guide Heat Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Calorie is the unit of
(a) heat
(b) work
(c) temperature
(d) food
Answer:
(a) heat

Question 2.
SI unit of temperature is
(a) fahrenheit
(b) joule
(c) Celsius
(d) kelvin
Answer:
(d) kelvin

Question 3.
Two cylindrical rods of same length have the area of cross section in the ratio 2:1. If both the rods are made up of same material, which of them conduct heat faster?
(a) Both rods
(b) Rod-2
(c) Rod-1
(d) None of them
Answer:
(c) Rod-1

Question 4.
In which mode of transfer of heat, molecules pass on heat energy to neighbouring molecules without actually moving from their positions?
(a) Radiation
(b) Conduction
(c) Convection
(d) Both B and C
Answer:
(a) Radiation

Question 5.
A device in which the loss of heat due to conduction, convection and radiation is minimized is
(a) Solar cell
(b) Solar cooker
(c) Thermometer
(d) Thermos flask
Answer:
(d) Thermos flask

II. Fill in the blanks:

1. The fastest mode of heat transfer is ……………………….
Answer:
radiation

2. During day time, air blows from ……………………… to………………………
Answer:
sea to land

3. Liquids and gases are generally ……………………… conductors of heat.
Answer:
poor

4. The fixed temperature at which matter changes state from solid to liquid is called………………………
Answer:
melting point

III. Assertion and Reason type questions :

Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion : Food can be cooked faster in vessels with copper bottom.
Reason : Copper is the best conductor of heat.
Answer:
(a) Both assertion and reason are true and reason is the correct explanation of assertion

Question 2.
Assertion : Maximum sunlight reaches earth’s surface during the noon time.
Reason : Heat from the sun reaches earth’s surface by radiation.
Answer:
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
Reason : When the sun is at its highest point, the earth’s surface absorbs more heat and retains. This heat is slowly radiated out causing increase in temperature.

Question 3.
Assertion : When water is heated up to 100° C, there is no raise in temperature until all water gets converted into water vapour.
Reason : Boiling point of water is 10° C.
Answer:
(c) Assertion is true but the reason is false
Reason : When a substance changes from one state to another, a considerable amount of heat energy is absorbed or liberated. This energy is called latent heat.

IV. Answer briefly :

Question 1.
Define conduction.
Answer:
The process of transfer of heat in solids from a region of higher temperature to a region of lower temperature without the actual movement of molecules is called conduction.

Question 2.
Ice is kept in a double-walled container. Why?
Answer:
An ice-box is made of double wall and the space between the walls is filled with some non-conducting materials to provide heat insulation, so that the loss of heat can be minimized. Hence ice is kept in a double-walled container.

Question 3.
How does the water kept in an earthen pot remain cool?
Answer:
An earthen pot consists of small pores from which the water inside the pot constantly seeps out and gets evaporated due to the presence of high temperatures around it. The evaporation process requires heat which is acquired from the surface of the pot, hence making the water and the pot cooler.

Question 4.
Differentiate convection,and radiation.
Answer:
Convection

1. The process of transfer of heat in which the heated molecules of a liquid (or gas) themselves move to carry heat from the hot to the cold end is called convection.
2. Ex : Land and sea breeze.
3. Convection need matter to be present.

Radiation

1. The process of transfer of heat in which a material medium is not necessary and heat is directly transferred from the hot body to the cold body is called radiation.
2. Ex : Transfer of heat energy from the sun.
3. Radiation can occur even in a vacuum.

Question 5.
Why do people prefer wearing white clothes during summer?
Answer:
People prefer white or light coloured clothes during summer as they are good reflectors of heat and hence, they keep us cool.

Question 6.
What is specific heat capacity?
Answer:
Specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of 1 kg of the substance by 1°C or 1 K.

Question 7.
Define thermal capacity.
Answer:

• Heat capacity or thermal capacity is defined as the amount of heat energy required to raise the temperature of a body by 1°C. It is denoted by ‘C’.
• C = Q/t, where C’ is the heat capacity, ‘Q’ is the quantity of heat required and ‘f’ is rise in temperature.
• SI unit of heat capacity is J/K. It is also expressed in cal/°C, kcal/°C or J/°C.

Question 8.
Define specific latent heat capacity.
Answer:
Specific latent heat is the amount of heat energy absorbed or liberated by unit mass of a substance during change of state without causing any change in temperature.

V. Answer in detail :

Question 1.
Explain convection in daily life.
Answer:
Convection is the flow of heat through a fluid from places of higher temperature to places of lower temperature by movement of the fluid itself.

Hot air balloons:
Air molecules at the bottom of the balloon get heated by a heat source and rise. As the warm air rises, cold air is pushed downward and it is also heated. When the hot air is trapped inside the balloon, it rises.

Breeze :
During day time, the air in contact with the land becomes hot and rises. Now the cool air over the surface of the sea replaces it. It is called sea breeze. During night time, air above the sea is warmer. As the warmer air over the surface of the sea rises, cooler air above the land moves towards the sea. It is called land breeze.

Chimneys :
Tall chimneys are kept in kitchen and industrial furnaces. As the hot gases and smoke are lighter, they rise up in the atmosphere.

Question 2.
What are the changes of state in water? Explain.
Answer:

• The process of changing of a substance from one physical state to another at a definite temperature is defined as change of state.
  
• For example, water molecules are in liquid state at normal temperature.
• When water is heated to 100°C, it becomes steam which is a gaseous state of matter. On reducing the temperature of the steam it becomes water again.
• If we reduce the temperature further to 0°C, it becomes ice which is a solid state of water. Ice on heating, becomes water again.
• Thus, water changes its state when there is a change in temperature.
• The process in which a solid is converted to liquid by absorbing heat is called melting or fusion.
• The process in which a liquid is converted to solid by releasing heat is called freezing.
• The process in which a liquid is converted to vapor by absorbing heat is called boiling or vaporization.
• The process in which a vapour is converted to liquid by releasing heat is called condensation.
• The process in which a solid is converted to gaseous state is called sublimation.

Question 3.
How can you experimentally prove water is a bad conductor of heat? How is it possible to heat water easily while cooking?
Answer:
Answer:
(a) Half fill a test tube with cold water. Wrap a piece of ice in wire gauze and drop it in the tube.
(i) It will sink to the bottom.
(ii) Now heat the top end of the test tube.
(iii) The water soon begins to boil at the top but the ice below has still not fully melted.

This activity shows that water is a bad conductor of heat. It does not easily conduct heat from the top to the bottom of the test tube.

(b) It is possible to heat water easily while cooking:

• ill a test tube with cold water.
• Drop an ice-cube in this water.
• Now heat the water from below.
• You will find that the ice melts quickly.
  This shows that though water is a bad conductor of heat, heat easily flows upwards in it. This method of transfer of heat is called convection. This method is involved in cooking.

VI. Numerical Problems.

Question 1.
What is the heat in joules required to raise the temperature of 25 grams of water from 0°C to 100°C? What is the heat in Calories? (Specific heat of water = 4.18 J/g°C)
answer:
Given : Mass of water m = 25g
Initial temperature T₁ = 0°C
Final temperature T₁ = 100°C
Change in temperature ΔT = (T₂ – T₁)
= (100 – 0)°C [ΔT= 100°C]
Specific heat of water C = 4.18 J/g°C
Solution:
The heat required H (in joules) = m × c × ΔT
= 25 × 4.18 × 100
= 25 × 418
= 10450 J
Heat required in calories = 1 calorie = 4.18 J
10450 J = 2497.60 calories

Question 2.
What could be the final temperature of a mixture of 100 g of water at 90°C and 600 g of water at 20°C.
Answer:
Mass of water m₁ = 100 g = 0.1 kg
Specific heat capacity of water c = 4186 J
Temperature = 90°C
Mass of water m₂ = 600 g = 0.6 kg
Temperature = 20°C
Solution:
Heat lost by hot water = Heat gained by cold water
m₁ × c × θ₁ = m₂ × c × θ₂
0.1 × 4186 x (90 – T_F) = 0.6 × 4186 × (T_F – 20)
0.1 × (90 – T_F) = (T_F – 20) × 0.6
9 – 0.1 T_F = 0.6T_F – 12
0.7T_F = 21
T_F = 30°C
Final temperature of a mixture = 30°C

Question 3.
How much heat energy is required to change 2 kg of ice at 0°C into water at 20°C? (Specific latent heat of fusion of water = 3,34,000J/kg, Specific heat capacity of water = 420OJKg^-1K^-1
Solution:
Mass of ice m = 2 kg
Specific latent heat of fusion of water = L = 3, 34, 000 J/kg
Change in temperature ΔT = (T₂ – T₁)
= (20 – 0)° C
ΔT = 20° C
Specific heat capacity of water C = 4200 J Kg^-1K^-1
Heat energy required= m × c × ΔT + m × L
= 2 × 4,200 × 20 + 2 × 3,34,000
= 1,68,000 + 6,68,000
Heat Energy required = 8,36,000 J

Intext Activities

ACTIVITY – 1

Take a glass of water and put some ice cubes into it. Observe it for some time. What happens? The ice cubes melt and disappear. Why did it happen? It is because heat energy in the water is transferred to the ice.

Aim:
To demonstrate transfer of heat.

Material required :
A glass of water, ice cubes.

Procedure:
Take a glass of water and put some ice cubes into it. Observe it for some time. What happens?

Observation :
The ice cubes melt and disappear. It is because heat energy in the water is transferred to the ice.

Conclusion :
Heat transfer takes place when heat energy flows from the object of higher temperature to an object with lower temperature.
[End of the activity]

ACTIVITY – 2

Take metal rods of copper, aluminum, brass and iron. Fix a match stick to one end of each rod using a little melted wax. When the temperature of the far ends reach the melting point of wax, the matches drop off. It’s observed that the match stick on the copper rod would fall first, showing copper as the best conductor followed by aluminum, brass and iron.

Aim :
To compare the conducting powers of various metals.

Materials required :
Metal roads of copper, aluminium, brass and iron, match stick, melted wax.

Procedure :
Fix a match stick to one end of each rod using the little melted wax. When the temperature of the far ends reach the melting point of wax, the matches drop. Observe what happens?

Observation :
The match stick on the copper rod would fall first, showing copper as the best conductor followed by aluminum, brass and then iron.

Conclusion:
Metals are good conductors of heat. Copper is the best conductor of heat.
[End of the activity]

ACTIVITY – 3

Drop a few crystals of potassium permanganate down to the bottom of a beaker containing water. When the beaker is heated just below the crystals, by a small flame, purple streaks of water rise upwards and fan outwards.

Aim :
To demonstrate transfer of heat through convection in liquids.

Materials required :
Crystals of potassium permanganate, beaker containing water.

Procedure :
Drop a few crystals of potassium permanganate down to the bottom of a beaker containing water, heat it with a small flame.

Observation :
When the beaker is heated, just below the crystals purple streaks of water rise upwards and fan outward.

Conclusion :
Water molecules at the bottom of the beaker receive heat energy and move upward and replace the molecules at the top.
This activity shows that the flow of heat through a fluid from places of higher temperature to places of lower temperature by movement of the fluid itself.
[End of the activity]

ACTIVITY – 4

Take some crushed ice cubes in a beaker and note down the temperature using thermometer. It will be 0°C. Now heat the ice in the beaker. You can observe that ice is melting to form water. Record the temperature at regular intervals and it will remain at 0°C until whole ice is converted to liquid. Now heat the beaker again and record the temperature. You can notice that the temperature will rise up to 100°C and it will retain the same even after continuous heating until the whole mass of water in the beaker is vaporized.

Aim :
To understand latent heat of the water.

Materials Required :
Crushed ice cubes, beaker and thermometer.

Procedure :
Take some crushed ice cubes in a beaker and note down the temperature using thermometer. It will be 0°C. Now heat the ice in the beaker, (i) Observe and record the temperature at regular intervals. Heat the beaker again and record the temperature.

Observation :

• Ice is melting to form water.
• Water will remain at 0°C until the whole ice is converted to liquid.
• On further heating, we can observe that the temperature will rise up to 100°C and the temperature will be at 100°C even after continuous heating until the whole mass of water in the beaker is vapourized.

Conclusion :
In this activity, the temperature is constant at 0°C until entire ice is converted into liquid and again constant at 100°C until all the water is converted into vapour.
It is because, when a substance changes from one state to another, a considerable amount of heat energy is absorbed or liberated. This energy is called latent heat.

9th Science Guide Heat Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
Water is used as a coolant because it ………………….
(a) is inexpensive
(b) is easily available
(c) is a good conductor of heat
(d) has a high specific heat capacity
Answer:
(d) has a high specific heat capacity

Question 2.
The amount of heat required to raise the temperature through 1°C is called………………………
(a) thermal energy
(b) calorie
(c) heat capacity
(d) specific heat capacity
Answer:
(c) heat capacity

Question 3.
The temperature at which a liquid gets converted into its vapour state is called its………………………
(a) melting point
(b) boiling point
(c) dew point
(d) freezing point
Answer:
(b) boiling point

Question 4.
Sweating causes cooling because water has a………………………
(a) high specific heat
(b) low specific heat
(c) high latent heat of fusion
(d) high latent heat of vaporisation
Answer:
(d) high latent heat of vaporisation

Question 5.
Which of the following is true?
(a) 1 J = 412 calorie
(b) 1 J = 0.24 calorie
(c) 1 calorie = 4.2 J
(d) Both b and c
Answer:
(c) 1 calorie = 4.2 J

Question 6.
Ice does not melt rapidly because of
(a) high specific heat capacity
(b) high latent of fusion
(c) high heat capacity
(d) high latent heat of fusion
Answer:
(d) high latent heat of fusion

Question 7.
Which one of the following scales has a lower fixed point at 0°C?
(a) Kelvin scale
(b) Fahrenheit scale
(c) Celsius scale
(d) All of these
Answer:
(c) Celsius scale

Question 8.
When we heat one end of an iron rod, its other end also gets heated. Can you say, Which one of the following is behind this?
(a) Convection of heat
(b) Radiation of heat
(c) Insulation of heat
(d) Conduction of heat
Answer:
(d) Conduction of heat

Question 9.
In which of the following, chemical energy is converted into heat energy?
(a) Heater
(b) Refrigerators
(c) Candle
(d) Motor
Answer:
(c) Candle

Question 10.
On a cold day, it is hard to open the lid of a tight container. But when you gently heat the neck you can easily open the lid. why?
(a) On heating glass expands and lid contracts
(b) On heating lid expands more than the neck and thus slides easily
(c) Neck becomes slippery on heating
(d) Lid of the bottle cannot bear the heat.
Answer:
(b) On heating lid expands more than the neck and thus slides easily

Question 11.
Warm air is ………………………
(a) lighter than cold air
(b) heavier than cold air
(c) both have equal weights
(d) cannot be said
Answer:
(a) lighter than cold air

Question 12.
The phenomenon involved in the sea breeze and the land breeze is ………………………
(a) convection
(b) conduction
(c) radiation
(d) none of these
Answer:
(a) convection

Question 13.
A liquid changes into a gas at a constant temperature known as its………………………
(a) absolute zero
(b) boiling point
(c) evaporation point
(d) dew point
Answer:
(b) boiling point

Question 14.
Copper and Iron are good conductors of heat. Which one of the following is not a good conductor of heat?
(a) Soil
(b) Aluminium
(c) Tungsten
(d) Steel
Answer:
(a) Soil

Question 15.
The specific heat capacity of water is
(a) 4200 Jkg^-1K^-1
(b) 420 Jg^-1K^-1
(c) 0.42 Jg^-1K^-1
(d) 4.2 Jkg^-1K^-1
Answer:
(a) 4200 Jkg^-1K^-1

Question 16.
Two cylinders of equal height and radius are made of copper and aluminum. Which of them conducts heat faster?
(a) Copper rod
(b) Aluminium rod
(c) Both of them
(d) None of them
Answer:
(a) Copper rod

II. Fill in the blanks:

1. ………………………is a process which is just reverse of melting.
Answer:
Freezing

2. While a substance is undergoing a change of state, the temperature of the body remains ………………………
Answer:
same

3. A change of state is a change of a substance from………………………
Answer:
one physical state to another

4. ………………………is the degree of hotness or coldness of a body.
Answer:
Temperature

5. The solid, liquid, gaseous phases of water can coexist in equilibrium at………………………
Answer:
273.16K

6. The sum of the kinetic and potential energy is called the ………………………of the molecules.
Answer:
internal energy

7. ……………………… is greater for liquids than that for solids and maximum in case of gases.
Answer:
Expansion

8. When heat energy is added to a substance, the kinetic energy of its particles and so the particles ……………………… move at a higher speed.
Answer:
increase

9. When a dog keeps out its tongue and breathes hard, the moisture on the tongue turns into ………………………and it evaporates.
Answer:
water

10. Black marks appearing on the ceiling above a lamp or fan caused by dust being carried upwards in the air are due to………………………
Answer:
convection currents

11. ………………………is the method of heat transfer that does not require particles to carry the heat energy.
Answer:
Radiation

12. Radiation consists of ………………………waves travelling at the speed of light.
Answer:
electromagnetic

13. We can observe all the three ways of heat transfer while………………………
Answer:
burning wood

14. ……………………… is known as an absolute scale.
Answer:
Kelvin

15. Specific latent heat L =………………………
Answer:
Q/m

III. Match the following :

Column A	Column B
1. Heat	a) Heat gained or lost in the change of state with out any change in temperature
2. m × L.	b) Heat gained or lost when there is no change of state
3. Temperature	c) Form of energy
4. m × s × t	d) SI unit of specific latent heat
5. J/Kg	e) degree of hotness or coldness

Answer:
1-c, 2 -a, 3 — e, 4-b, 5-d

II.

Column A	Column B
1. Specific heat capacity of water	a) 0°C
2. Latent heat of fusion of ice	b) 2260 J/g
3. Latent heat of vaporisation of water	c) 100°C
4. Melting point of ice	d) 4.2 J/g°C
5. Boiling point of water	e) 336 J/g

Answer:
1-d, 2 -e, 3 – b, 4-a, 5-c

IV. Assertion and Reason type questions :

Question 1.
Assertion (A) : Temperature is the measure of heat energy.
Reason (R) : Energy is the capacity to do work.
(a) If both assertion and reason are true and the reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
Answer:
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
Reason: It is the degree of hotness or coldness of a body.

Question 2.
Assertion (A): Radiation is a process of transfer of heat in which a material medium is not necessary.
Reason (R): The heat from the sun reaches us through millions of miles of empty space by convection.
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
Answer:
(c) Assertion is true but reason is false
Reason : All hot bodies radiate’ heat, therefore from the sun the heat comes to us by radiation.

Question 3.
Assertion (A) : Heat energy is transferred from one body to another due to a
temperature difference between them.
Reason (R) : Heating a substance causes a rise in temperature.
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
Answer:
(b) Both assertion and reason are true but reason is not the correct explanation of assertion
Reason : Heat energy is more in hot substances and less in cold substances and flows from hot substances to cold substances.

Question 4.
Assertion (A) : When a very hot liquid is poured into a thick glass tumbler it cracks.
Reason (R) : Unequal expansion of the inner and outer glass walls causes the glass to crack.
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
Answer:
(a) Both assertion and reason are true and reason is the correct explanation of assertion

V. Very short answer type questions.

Question 1.
What is the other name of heat capacity?
Answer:
Thermal capacity.

Question 2.
Define one calorie.
Answer:
The amount of heat energy required to raise the temperature of 1 g water by 1°C is called one calorie.

Question 3.
What is the relation between calorie and Joule?
Answer:
1 Calorie = 4.186 J
= 4.2 J

Question 4.
Name a device that prevents loss of energy (or gain) by conduction, convection and radiation.
Answer:
Thermos flask.

Question 5.
Which factor determines the direction of flow of heat from one body to another?
Answer:
Temperature.

Question 6.
Who introduced the term latent heat?
Answer:
Joseph Black in 1750.

Question 7.
What is the minimum possible temperature? Is there also a maximum possible temperature?
Answer:
The minimum possible temperature is OK. There is no limit to maximum temperature.

VI. Answer briefly :

Question 1.
Heat gained by a body depends upon which factors?
Answer:

• Mass of the body
• Change in temperature of the body
• Nature of the material of the body.

Question 2.
Water is used as a coolant in car radiators. Why?
Answer:
Water is used as a coolant in car radiators because it has high specific heat capacity. As a result, it can absorb large amounts of heat from the car engine without any substantial increase in its temperature.

Question 3.
What do you mean by thermal equilibrium?
Answer:
When two bodies at different temperatures are kept in contact with each other, then heat energy flows from the hot body to the colder one.

It means that the hot body will lose heat and the cold body will gain heat till they reach a common temperature. This state is called thermal equilibrium.

Question 4.
Define latent heat of fusion?
Answer:
Heat energy is absorbed by a solid during melting and an equal amount of heat energy ‘ is liberated by the liquid during freezing, without any temperature change. It is called latent heat of fusion.

Question 5.
Why are burns caused by steam more painful than those caused by boiling water at the same temperature?
Answer:

• When steam hits our skin, it condenses to water and then cools down to the temperature of skin.
• Now, the energy released will be due to latent heat and fall in temperature.
• Whereas when boiling water hits our skin, there is no phase transition but only fall in temperature and the heat transferred to skin will be only due to cooling.
• Also, the loss of energy that is released from steam hitting our skin occurs quickly and in a small localized area, therefore causing damage to our cells.

Question 6.
What do you mean by solidification or deposition?
Answer:
Solidification is the process in which a gas directly condenses into its solid state without going into liquid state Ex : Carbon dioxide gas gets converted into dry ice.

Question 7.
Define absolute zero.
Answer:
The temperature at which the pressure and volume of a gas theoretically reaches zero is called absolute zero.

Question 8.
Give some practical applications of conduction in daily life.
Answer:

• Metals are good conductors of heat. So, aluminium is used for making utensils to cook food quickly.
• Mercury is used in thermometers because it is a good conductor of heat.
• We wear woolen clothes in winter to keep ourselves warm. Air, which is a bad conductor, does not allow our body heat to escape.

Question 9.
Give some practical applications of radiation.
Answer:

• White or light colored clothes are good reflectors of heat. They keep us cool during summer.
• The bottom surface of cooking utensils is blackened because the black surface absorbs more heat from the surrounding.
• The surface of the airplane is highly polished because it helps to reflect most of the heat radiation from the sun.

Question 10.
Can convection take place in solids? Why?
Answer:
No. The molecules in a solid are only free to vibrate about their fixed positions. For convection to take place, the molecules need to move to carry the heat with them. Hence, convection cannot take place in solids.

Question 11.
In winters, when the sun suddenly goes behind the clouds we feel cold, can you say why?
Answer:
The clouds cut off the radiant heat from the sun.

VII. Answer in detail :

Question 1.
Give the difference between heat and temperature.
Answer:
Heat

1. Heat is a form of energy due to which we feel hot or cold.
2. Its SI unit is joule (J)
3. It depends upon mass, nature and temperature of the body.
4. It is a form of energy.
5. It is measured by a calorimeter.

Temperature :

1. The degree of hotness or coldness of a body is known as temperature.
2. Its SI unit is kelvin (K).
3. It does not depend upon mass, nature and temperature of the body.
4. It is a condition that determines the direction of flow of heat.
5. It is measured by a thermometer.

Question 2.
Give some practical applications of specific latent heat of ice.
Answer:
Specific latent heat of ice is very high (i.e.) 336 J/g.

• Due to high specific latent heat of ice, snow on mountains do not melt as a whole, but melts gradually into water with the heat of the sun.
  If the specific latent heat of ice would not have been so high, all the snow would have melted very quickly and there would have been floods in the rivers.
• All the water in lakes and ponds in cold places do not freeze all at the same time. If freezes slowly and keeps the surrounding moderate.
• Drinks are cooled more effectively by ice pieces at 0°C and not by water at 0°C. This is because 1 g of ice takes away 336 J of heat from the drink to melt into water at 0°C.

Question 3.
600 g of copper at 50°C is mixed with lOOOg water at 20°C. Find the final temperature of the mixture. Specific heat capacity of copper is 0.4 Jg^-1°C^-1 and that of water is 4.2 Jg^-1°C^-1
Solution :
Let final temperature of the mixture of copper and water = x °C
For copper:
Mass of copper m₁ = 600g
Specific heat capacity of copper c₁ = 0.4Jg^-1°C^-1
Initial temperature of copper t₁ = 50°C
Final temperature of copper t₂ = x°C
Fall in temperature Δt = (50 – x)°C
Heat lost by copper = m₁ × c₁ × t
= 600 × 0.4 × (50 – x)

For water :
Mass of water m₂ = 1000g
Specific heat capacity of water c₂ = 4.2Jg^-1°C^-14
Initial temperature of water t₁ = 20°C
Final temperature of water t₂ = x°C
Rise in temperature Δt = (x – 20)°C
Heat gained by water = m₂ × c₂ × t
= 100 × 4.2 × (x – 20)

According to the principle of calorimetry,
Heat lost by copper = Heat gained by water
600 × 0.4 × (50 – x) =1000 x 4.2 x (x – 20)
240 × (50 – x) = 4200 ( x- 20)
12,000 – 240x = 4200x-84000
4200x + 240x =12000 + 84000
4440 = 96000
x = \(\frac{96000}{4440}=21.6\)
So, final temperature of mixture of water and copper x = 21.6°C

Question 4.
Compare heat capacity and specific heat capacity.
Answer:
Specific heat capacity :

1. It is the heat required to raise the temperature of 1g of a substance through 1°C.
2. It does not depend on the mass of the body It depends on the mass of the body
3. Its unit is Jkg^-1 °C^-1

Heat capacity

1. It is the heat required to raise the temperature of a given mass of substance through 1°C.
2. It depends on the mass of the body
3. Its unit is J°C^-1.

Question 5.
Explain the following effects of heat.
(i) Expansion
(ii) Change in temperature
(iii) Change in state
(iv) Chemical changes.
Answer:
(i) Expansion:
When heat is added to a substance, the molecules gain energy and vibrate and force other molecules apart. As a result, expansion takes place. You would have seen some space being left in railway tracks. It is because, during summer time, more heat causes expansion in tracks. Expansion is greater for liquids than for solids and maximum in case of gases.

(ii) Change in temperature :
When heat energy is added to a substance, the kinetic energy of its particles increases and so the particles move at higher speed. This causes rise in temperature. When a substance is cooled, that is, when heat is removed, the molecules lose heat and its temperature falls.

(iii) Change in state :
When you heat ice cubes, they become water and water on further heating changes into vapour. So, solid becomes liquid and liquid becomes gas, when heat is added. The reverse takes place when heat is removed.

(iv) Chemical changes :
Since heat is a form of energy it plays a major role in chemical changes. In some cases, chemical reactions need heat to begin and also heat determines the speed at which reactions occur. When we cook food, we light the wood and it catches fire and the food particles become soft because of the heat energy. These are all the chemical changes taking place due to heat.

VIII. Numerical Problems

Question 1.
What is the amount of heat required to raise the temperature of 5 kg of iron from 30°C to 130°C? Specific heat capacity of iron = 483 Jkg^-1C^-1.
Solution :
Mass of iron m = 5kg
Initial temperature t₁ = 30°C
Final temperature t₂ = 130°C
Rise is temperature Δt = (t₂ -t₁) = 130 – 30 = 100°C
Specific heat capacity of iron c = 483Jkg^-1°C^-1
Q = m × c × Δt
= 5 × 483 × 100
= 2,41,500J

Question 2.
Calculate the amount of heat required to convert 200g of ice at 0°C into the water at 0°C Specific latent heat of fusion of ice = 336 Jg^-1
Solution :
Mass of ice m = 200g
Specific latent heat of fusion of ice L = 336Jg^-1
Heat required Q = mL
= 200 × 336
Q = 67,200 J

Question 3.
2875 J of heat is required to melt 115 g of lead at its melting point. Calculate the specific latent heat capacity of fusion of lead.
Solution:
Mass of lead m = 115 g
Heat required Q = 2875 J
Specific latent heat of lead L =?
We know that Q = m L
L = \(\frac{Q}{m}=\frac{2875}{115}\)
= 25 Jg^-1

Question 4.
What will be the final temperature if 1,68,000 J of heat is absorbed by 2 kg of water at 30°C?
Solution :
Heat absorbed Q = 1,68,000 J
m = 2kg
Initial temperature t₁ = 30°C
Let final temperature t₂ = x°C
Rise is temperature Δt = (t₂ – t₁)
= (x – 30)°C
Specific heat capacity of water C = 4200 J kg^-1°C^-1
We know that Q = m × c × Δt
1,68,000 = 2 × 4200 × (x – 30 )
x – 30 = \(\frac{1,68,000}{2 \times 4200}\)
x- 30 = 20
x = 30 + 20
= 50°C
So, the final temperature of water = 50°C

Question 5.
A metal ball of heat capacity 50J/°C loses 2000 J of heat. By how much will its temperature fall?
Solution :
Heat capacity of ball = 50 J °C^-1
Heat lost Q = 200 J
Fall in temperature t =?

IX. Convert the following

1. 100°F to °C
Solution:
T(°C) = (T(°F) – 32) /1.8
T(°C) = (100°F – 32)
T(°C) = 37.7 °C

2. 40°C to Fahrenheit (°F)
Solution :
T(°F) = (T(°F) × 1.8) + 32
= 40°C × 1.8 + 32
= 72 + 32
T(°F) = 104°F

3. 35°C to Kelvin
Solution :
T(K) = T(°C) +273.15
= 35 + 273.15
T(K) = 308.15 K

4. 80°K to °C
Solution :
T(°C) = T(K) – 273.15
T(°C) = 80-273.15
T(°C) = 193.I5 °C

X. Define the following :

1. Heat: Heat is a form of energy which transfers from the higher temperature region to the lower temperature region of a body.
2. Conduction: The process of transfer of heat in solids from a region of higher temperature
to a region of lower temperature without the actual movement of molecules is called conduction.
3. Convection: Convection is the flow of heat through fluid from places of higher temperature to places of lower temperature by the movement of the fluid itself.
4. Radiation: Radiation is a method of heat transfer that does not require particles to carry the heat energy.
5. Temperature: Temperature is the degree of hotness or coolness of a body.
6. Specific heat capacity: Specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of 1 kg of the substance by 1° C or 1 K.
7. Heat capacity or thermal capacity: Heat capacity is the heat required to raise the temperature of the entire mass of the body by 1° C.
8. Change of state: The process of changing of a substance from one physical state to another at a definite temperature is known as change of state.
9. Melting or fusion: The process in which a solid is converted to a liquid by absorbing heat is called melting or fusion.
10. Boiling: Th e process in which a liquid is converted to vapor by absorbing heat is called boiling or vaporization.
11. Sublimation: Th e process in which a solid is converted to a gaseous state is called sublimation.
12. Latent heat: Thus, latent heat is the amount of heat energy absorbed or released by a substance during a change in its physical states without any change in its temperature.
13. Specific latent heat: Specific latent heat is the amount of heat energy absorbed or liberated by the unit mass of a substance during a change of state without causing any change in temperature.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 6 Light Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 6 Light

9th Science Guide Light Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
A ray of light passes from one medium to another medium. Refraction takes place when angle of incidence is
(a) 0°
(b) 45°
(c) 90°
Answer:
(c) 90°

Question 2.
is used as reflectors in torchlight.
(a) Concave mirror
(b) Plane mirror
(c) Convex mirror
Answer:
(a) Concave mirror

Question 3.
We can create enlarged, virtual images with
(a) concave mirror
(b) plane mirror
(c) convex mirror
Answer:
(a) concave mirror

Question 4.
When the reflecting surface is curved outwards the mirror formed will be
(a) concave mirror
(b) convex mirror
(c) plane mirror
Answer:
(b) convex mirror

Question 5.
When a beam of white light passes through a prism it gets
(a) reflected
(b) only deviated
(c) deviated and dispersedAnswer:
(c) deviated and dispersed

Question 6.
The speed of light is maximum in
(a) vacuum
(b) glass
(c) diamond
Answer:
(a) vacuum

II. State whether true or false. If false, correct the statement :

1. The angle of deviation depends on the refractive index of the glass.
Answer:
True

2. If a ray of light passes obliquely from one medium to another, it does not suffer any deviation.
Answer:
False.
Correct statement: If a ray of light passes obliquely from one medium to another, it bends and from the normal.

3. The convex mirror always produces a virtual, diminished and erect image of the object.
Answer:
True.

4. When an object is at the centre of curvature of concave mirror the image formed will be virtual and erect.
Answer:
False.
Correct statement: When an object is at the centre of curvature of concave mirror the image formed will be real and inverted.

5. The reason for brilliance of diamonds is total internal reflection of light.
Answer:
True.

III. Fill in the blanks :

1. In going from a rarer to denser medium, the ray of light bends ……………………….
Answer:
towards the normal

2. The mirror used in search light is ……………………….
Answer:
concave

3. The angle of deviation of light ray in a prism depends on the angle of . ……………………….
Answer:
incidence

4. The radius of curvature of a concave mirror whose focal length is 5cm is ………………………..
Answer:
10 cm

5. Large ……………………….mirrors are used to concentrate sunlight to produce heat in solar furnaces.
Answer:
concave

IV. Match- the following :

Ratio of height of image to height of object.	Concave mirror
Used in hairpin bends in mountains.	Total internal reflection
Coin inside water appearing slightly raised.	Magnification
Mirage	Convex mirror
Used as Dentist’s mirror.	Refraction

Answer:

Ratio of height of image to height of object.	Magnification
Used in hairpin bends in mountains.	Convex mirror
Coin inside water appearing slightly raised.	Refraction
Mirage	Total internal reflection
Used as Dentist’s mirror.	Concave mirror

V. Assertion & Reason :

Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation.
(b) If both assertion and reason are true and reason is not the correct explanation.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true

Question 1.
Assertion: For observing the traffic at a hairpin bend in mountain paths a plane mirror is preferred over the convex mirror and concave mirror.
Reason: A convex mirror has a much larger field of view than a plane mirror or a . concave mirror.
Answer:
(d) Assertion is false but reason is true

Question 2.
Assertion: The incident ray is directed towards the centre of curvature of spherical mirror. After reflection it retraces its path.
Reason : Angle of incidence (i) = Angle of reflection (r) = 0°.
Answer:
(a) Both assertion and reason are true and reason is the correct explanation

VI. Answer very briefly:

Question 1.
According to cartesian sign convention, which mirror and which lens has negative focal length?
Answer:
Concave mirror is having a negative focal length.

Question 2.
Name the mirror(s) that can give (i) an erect and enlarged image, (ii) same sized, inverted image.
Answer:
Concave mirror.

Question 3.
If an object is placed at the focus of a concave mirror, where is the image formed?
Answer:
The image will be formed at infinity as real and inverted.

Question 4.
Why does a ray of light bend when it travels from one medium to another?
Answer:
A ray of light bend when it travels from one medium to another due to the change in velocity of light in two different medium.

Question 5.
What is the speed of light in vacuum?
Answer:
The speed of light in vacuum is known to be almost exactly 300,000 km per second. In 1665 the Danish astronomer Ole Roemer first estimated the speed of light by observing one of the twelve moons of the planet Jupiter.

Question 6.
Concave mirrors are used by dentists to examine teeth. Why?
Answer:
As concave mirror produces virtual, erect and magnified images when an object is placed in

VII. Answer briefly :

Question 1.
a) Complete the diagram to show how a concave mirror forms the image of the object.
b) What is the nature of the image?

Answer:
a)

b) Real, inverted and magnified.

Question 2.
Pick out the concave and convex mirrors from the following and tabulate them. Rear-view mirror, Dentist’s mirror, Torch-light mirror, Mirrors in shopping malls, Make-up mirror.
Answer:

Concave Mirror	Convex Mirror
Dentist’s mirror	Rearview mirror
Torchlight mirror	Mirrors in shopping malls
Makeup mirror

Question 3.
State the direction of the incident ray which after reflection from a spherical mirror retraces its path. Give a reason for your answer.
Answer:
When an incident ray is directed towards the centre of curvature, at all the points of the spherical mirror, the ray is always normal. Therefore, angle of incidence i = Angle of reflection r = 0°.

Question 4.
What is meant by magnification? Write its expression. What is its sign for real image and virtual image?
Answer:
Magnification is the increase in size of an image compared to true size.

(a) Negative sign – real image
(b) Positive sign – virtual image

Question 5.
Write the spherical mirror formula and explain the meaning of each symbol used in it.
Answer:
The expression relating the distance of the object u, distance of image v and focal length/of a spherical mirror is called the mirror equation. It is given as:
Mirror formula: \(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)
Here, f – focal length of spherical mirror; u – distance of the objective; v – distance of the image.

VIII. Answer in detail :

Question 1.
a) Draw ray diagrams to show how the image is formed using a concave mirror, when the position of objeict is (i) at C (ii) between C and F (iii) between F and P of the mirror.
b) Mention the position and nature of image in each case.
Answer:
a) object At C
i)

(b) Position of an object: At C
Position of the image: At C

Nature of the image:
(i) Real
(ii) Inverted
(iii) Same size as the object

(ii) object At C and F

Position of the object: Between C and F
Position of the image: Beyond C

Nature of the image :
(i) Real
(ii) Inverted
(iii) Magnified

(iii) Object between F and P of the Mirror

Position of object : Between F and P
Position of the image : Behind the Mirror

Nature of the image :
(i) Virtual
(ii) Erect
(iii) Magnified

Question 2.
Explain with diagrams how refraction of incident light takes place from a) rarer to denser medium b) denser to rarer medium c) normal to the surface separating the two media.
Answer:
a) rarer to denser medium
When a ray of light travels from optically rarer medium to optically denser medium, it bends towards the normal.

b) denser to rarer medium
When a ray of light from an optically denser medium to an optically rarer medium it bends away from the normal.

c) normal to the surface separating the two media.
A ray of light incident normally on a denser medium it goes without any deviation.

IX. Numerical Problems:

Question 1.
A concave mirror produces three times magnified real image of an object placed at 7 cm in front of it. Where is the image located?
Answer:
Here given magnification m = 3
Object distance u = -7 cm
Magnification m = \(-\frac{v}{u}\) Real image
-3 = \(-\frac{v}{u}\)
3u = -v
v = 3u = 3 x 7 = 21 cm
The image will be formed at a distance of 21 cm in front of concave mirror from its pole.

Question 2.
Light enters from air into a glass plate having a refractive index of 1.5. What is the speed of light in glass?
Answer:
Refractive index of a glass plate μ = 1.5
Speed of light in vacuum is C = 3 x 10⁸ms^-1
Speed of light in glass V =?

speed of light in glass = 2 × 10⁸ms^-1

Question 3.
The speed of light in water is 2.25 × 10⁸ms^-1. If the speed of light in a vacuum is 3 × 10⁸ms^-1, calculate the refractive index of water.
Answer:
Speed of light in water V = 2.25 × 10⁸ms^-1
Speed of light in vacuum C = 3 × 10⁸ms^-1
Refractive index of water μ =?

X. Higher Order Thinking Skills.

Question 1.
Lightray emerges from water into the air. Draw a ray diagram indicating the change in its path in the water.
Answer:

Question 2.
When a ray of light passes from air into glass, is the angle of refraction greater than or less than the angle of incidence?
Answer:
Light bends towards the normal because glass is denser than air.
It bends towards normal since light has to travel with the lesser speed in the glass but within a short time.
r < i. The angle of refraction is less than the angle of incidence.

Question 3.
What do you conclude about the speed of light in diamond, if the refractive index of diamond is 2.41?
Answer:
Refractive index of diamond μ = 2.41

∴ Speed of light in a diamond (1.24 × 10⁸ms^-1) is less than the speed of light in air (3 × 10⁸ms^-1).
The refractive index of diamond is 2.42, it means that speed of light in air (vacuum) is 2.42 times the speed of light in a diamond.

Intext Activities

ACTIVITY – 1

Stand before the mirror in your dressing table or the mirror fixed in a steel almirah. Do you see your whole body? To see your entire body in a mirror, the mirror should be atleast half of your height. Height of the mirror= Your height/2.
Solution :
(i) If the height of a person is 5 feet, then he should use a plane mirror of 2Vi feet height and fix in a steal almirah.
(ii) Now if he stand before it his full body will be seen on the mirror because hight of the mirror = \(\frac{\text { Our hieight }}{2}\)

ACTIVITY – 2

Hold a concave mirror in your hand (or place it in a stand). Direct its reflecting surface towards the sun. Direct the light reflected by the mirror onto a sheet of paper held not very far from the mirror. Move the sheet of paper back and forth gradually until you find a bright, sharp spot of light on the paper. Position the mirror and the paper at the same location for few moments. What do you observe? Why does the paper catch fire?
Solution :
A concave mirror converges all the light rays coming from the Sun. All these light rays converge and meet at the focus of the mirror.
So, all the heat and light is focused on the principal focus (F). When a paper is kept at the focus (F), it starts burning, as this point is very hot.

ACTIVITY – 3

Take a convex mirror. Hold it in one hand. Hold a pencil close to the mirror in the upright position in the other hand. Observe the image of the pencil in the mirror. Is the image erect or inverted? Is it diminished or enlarged? Move the pencil slowly away from the mirror. Does the image become smaller or larger? What do you observe?

Solution :

1. When a pencil is held in the upright position in front of a convex mirror, its diminished, erect image is formed which is virtual and therefore seen in the convex mirror.
2. When the pencil is moved away from the convex mirror size of image becomes smaller and smaller but image remains erect.
3. As we move away, the object from the convex mirror, image shifts towards the focus.

ACTIVITY – 4

Refraction of light at air-water interface
Put a straight pencil into a tank of water or beaker of water at an angle of 45° and look at it from one side and above. How does the pencil look now?
The pencil appears to be bent at the surface of water.
Solution :

Both the above activities are the result of refraction of light. The bending of light rays when they pass obliquely from one medium to another medium is called refraction of light.

9th Science Guide Light Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
A ray of light is incident towards a plane mirror at an angle of 30° with the mirror surface. What will be the angle of reflection?
(a) 45°
(b) 30°
(c) 90°
(d) 60°
Answer:
(d) 60°

Question 2.
A 10 mm long bin is placed vertically in front of a concave mirror. A 5 mm long image of the bin is formed at 30 cm in front of the mirror. The focal length of this mirror is
(a) -20cm
(b) -30cm
(c) -60cm
(d) -40cm
Answer:
(a) – 20cm

Question 3.
A ray of light as it travels from medium A to medium B refractive index of the medium B relative to medium A is (μB/ μA)
(a) \(\frac{\sqrt{3}}{\sqrt{2}}\)
(b) \(\frac{\sqrt{2}}{\sqrt{3}}\)
(c) \(\frac{{1}}{\sqrt{2}}\)
(d) \(\sqrt{2}\)
Answer:
(b) \(\frac{\sqrt{2}}{\sqrt{3}}\)

Question 4.
Under which of the following conditions a concave mirror can form an image larger than the actual object?
(a) when the object is kept at a distance equal to its radius of curvature.
(b) when object is kept at a distance less than its focal length.
(c) when object is placed between the focus and centre of curvature
(d) when object is kept at a distance greater than its radius of curvature.
Answer:
(c) when object is placed between the focus and centre of curvature

Question 5.
In torches, searchlights and head lights of vehicles the bulb is placed …………………………… of the concave mirror.
(a) between and F of the reflector
(b) Very near to F
(c) between F & C
(d) at C
Answer:
(b) Very near to F

Question 6.
A boy is standing at a distance of 3m in front of a plane mirror. The distance between the boy and his image is ………………….. m
(a) 4
(b) 2
(c) 3
(d) 6
Answer:
(c) 3

Question 7.
The image formed by a concave mirror is real, inverted and of the same size as that of the object the position of the object should be
(a) beyond C
(b) between C & F
(c) at C
(d) at F
Answer:
(c) at C

Question 8.
Which of the following has the highest refractive index
(a) air
(b) water
(c) diamond
(d) glass
Answer:
(c) diamond

Question 9.
The image formed by a plane mirror is
(a) real
(b) diminished
(c) enlarged
(d) laterally inverted
Answer:
(d) laterally inverted

Question 10.
The incident ray passing through ‘F of a mirror ………………….. after reflection
(a) passes through C
(b) passes through F
(c) passes parallel to the principal axis
(d) passes through the pole
Answer:
(c) passes parallel to the principal axis

Question 11.
The incident ray passing through C of a mirror ………………….. after reflection.
(a) passes through C
(b) passes through F
(c) passes through P
(d) parallel to the principal axis
Answer:
(a) passes through C

Question 12.
The incident ray parallel to the principal axis of a mirror ………………….. after reflection.
(a) passes through C
(b) passes through F
(c) passes through P
(d) reverts back in the opposite direction
Answer:
(b) passes through F

Question 13.
According to sign convention the distance of the object.
(a) is always positive
(b) is always negative
(c) maybe positive or negative
(d) is equal to object height.
Answer:
(b) is always negative

Question 14.
According to sign convention the distance of the image.
(a) is always positive
(b) is always negative
(c) maybe positive or negative
(d) is equal to image height
Answer:
(c) maybe positive or negative

Question 15.
Total internal reflection will occur if the angle of reflection is
(a) 45°
(b) 60°
(c) 90°
(d) 99°
Answer:
(d) 99°

Question 16.
Magnification for the………………….. image is always …………………..
(a) real, positive
(b) real, negative
(c) virtual, negative
(d) virtual, positive
Answer:
(b) real, negative

Question 17.
If magnification is +1.5. The image is …………………..
(a) erect
(b) diminished
(c) real
(d) invected
Answer:
(a) erect

Question 18.
The refractive index of a denser medium with respect to rarer medium is
(a) 1
(b) greater than 1
(c) less than 1
(d) negative
Answer:
(b) greater than 1

Question 19.
We can see objects because of
(a) reflection
(b) refraction
(c) transmission
(d) diffraction
Answer:
(a) reflection

Question 20.
The image formed by a convex mirror is always
(a) real (b) enlarged
(c) virtual & enlarged
(d) diminished
Answer:
(d) diminished

Question 21.
As you move an object always from a convex mirror, its image becomes…………………..
and moves towards
(a) smaller, infinity
(b) smaller, focus
(c) enlarged, infinity
(d) enlarged, focus
Answer:
(b) smaller, focus

Question 22.
For a spherical mirror ………………….. is true.
(a) f = 2R
(b) R = 2f
(c) fR = 2
(d) fR = \(\frac { 1 }{ 2 }\)
Answer:
(b) R = 2f

Question 23.
The mirror formula is…………………..

Answer:
(c) \(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)

Question 24.
For a plane mirror, magnification m =
(a) 0
(b) 1
(c) ± 1
(d) ≤0
Answer:
(b) 1

Question 25.
Magnification for convex mirror is
(a) always positive
(b) always negative
(c) some times positive
(d) 1
Answer::
(a) always positive

Question 26.
If the angle of incidence i = 0, the angle of reflection r =
(a) 0°
(b) 90°
(c) 180°
(d) 45°
Answer:
(a) 0°

Question 27.
Refractive index of a medium is …………………..
(a) speed of light in air to speed of light in vacuum
(b) speed of light in vacuum to speed of light in air
(c) focal length to object distance
(d) speed of light in the medium × speed of light in the air
Answer:
(a) speed of light in air to speed of light in vacuum

Question 28.
Bending of light as it passes from one medium to another is called
(a) reflection
(b) diffraction
(c) refraction
(d) deviation
Answer:
(c) refraction

Question 29.
Ratio of sine of angle of incidence to sine of angle of refraction is ………………….
(a) gravitational law
(b) law of reflection
(c) law of refraction
(d) snell’s law.
Answer:
(d) snell’s law

Question 30.
Entire light is reflected back into denser medium is called
(a) total internal reflection
(b) refraction
(c) reflection
(d) total external refraction.
Answer:
(a) total internal reflection

Question 31.
Outer concentric shell in optic fiber is called
(a) cladding
(b) core
(c) mantel
(d) coat
Answer:
(a) cladding

Question 32.
When light is going from a denser to a less dense medium, the critical angle is the angle of incidence for which the angle of refraction is
(a) 48°
(b) 90°
(c) 42°
(d) 51°
Answer:
(b) 90°

Question 33.
A bundle of glass threads, each of which is capable of transmitting messages using light waves is called
(a) microscope
(b) convex
(c) periscope
(d) optic fibre
Answer:
(d) optic fibre

Question 34.
A ray of light travelling in medium 1 strikes and travels into another transparent medium 2. If the speed of light is greater in medium 1, the ray will
(a) refract towards the normal
(b) have an angle of incidence smaller than be angle of refraction
(c) refract away from the normal
(d) undergo total internal reflection
Answer:
(a) refract towards the normal

Question 35.
A ray of light travels from air into a glass block as shown. It makes an angle of 30° with the surface of the block. If the refractive index of the glass is 1.5, what will be the angle of refraction?

(a) 35.26°
(b) 1.30°
(c) 48.59°
(d) 19.47°
Answer:
(d) 19.47°

Question 36.
The field of view is maximum for …………………
(* FOV is the extent of the observable area that is seen at any given instant)
(a) plane mirror
(b) concave mirror
(c) convex mirror
Answer:
(c) convex mirror

Question 37.
A real and enlarged image can be obtained by using a
(a) convex mirror
(b) plane mirror
(c) concave mirror
Answer:
(c) concave mirror

Question 38.
Which of the following statements about total internal reflection is true?
(a) angle of incidence should be greater than the critical angle
(b) light must travel from a medium of higher refractive index to a medium of lower refractive index
(c) both (a) and (b)
Answer:
(c) both (a) and (b)

Question 39.
The focal length of a concave mirror is 5cm. Its radius of curvature is
(a) 5 cm
(b) 10 cm
(c) 2.5 cm
Answer:
(b) 10 cm

II. Fill in the blanks :

1. The ratio of the sine of the angle of incidence to the sine of …………………is constant.
Answer:
angle of refraction

2. A spherical mirror whose reflecting surface is curved outwards is called ………………… mirror.
Answer:
convex

3. All distances parallel to the principal axis are measured from the ………………… of the
mirror.
Answer:
pole

4. A negative sign in the value of magnification indicates that the image is …………………
Answer:
real

5. Light is refracted or bent while going from one medium to another because of its ………………… changes.
Answer:
speed

III. State whether true or false. If false, correct the statement:

1. The critical angle is defined as the angle of incidence at which the total internal reflection starts to occur.
Answer:
True.

2. The angle of incidence is equal to the angle of reflection for perfect reflection.
Answer:
True.

3. The image formed in a plane mirror is always inverted.
Answer:
False.
Correct statement: The image formed in a plane mirror is always erect.

4. A star appears twinkling into the sky because of the reflection of light by the atmosphere
Answer:
False.
Correct statement: A star appears twinkling into the sky because of the refraction of light by the atmosphere.

5. Mirage is an example of refraction and total internal reflection of light.
Answer:
True.

6. Optical Fibres are based on the phenomenon of dispersion
Answer:
False.
Correct statement: Optical Fibres are based on total internal reflection.

7. A water tank appears shallower when it is viewed from the top due to refraction.
Answer:
True.

8. Twinkling of stars and Mirage are the two phenomena occurring due to refraction.
Answer:
True.
Twinkling of stars and Mirage.

9. Angle of incidence is zero if a ray of light is incident normal to be surface separating the low media.
Answer:
True.

10. A real image is inverted and can be caught on the screen.
Answer:
True.

11. The minimum length of the mirror required to see the full image of the person is half ‘ of his height.
Answer:
true.

12. The pencil appears to be bent at the surface of the water is due to refraction.
Answer:
True.

13. The speed of light decreases in a denser medium, light bends towards the normal.
Answer:
True.

14. If the object is at infinity in front of a convex mirror the image is formed at infinity.
Answer:
False.
Correct statement: The image is formed at F, behind the mirror

15. An object is placed at a distance of 3cm from a plane mirror. The distance of the object and image is 3cm.
Answer:
False.
Correct statement: The distance of the object and image is 6 cm.

16. The distance from centre of curvature of the mirror to the pole is called the focal length of the mirror.
Answer:
False.
Correct statement: The distance between the centre of the mirror and the focal point of the mirror is called the focal length of a mirror.

17. Light is one of the slowest travelling energy with a speed of 3 × 10^-8ms^-1
Answer:
False.
Correct statement : (Light is one of the fastest travelling energy with a speed of 3 × 10^-8ms^-1

18. The angle of incidence at which the angle of refraction is Q£ is called the critical angle.
Answer:
False.
Correct statement: The angle of incidence at which the angle of refraction is 90° is called the critical angle.

IV. Match the following :

Question 1.

Column I	Column II
(i) A plane mirror	(a) Image is erect & smaller in size than the object.
(ii) A concave mirror	(b) Image is erect & of the same size as of the object.
(iii) A convex	(c) Used by dentists to see an enlarged images of teeth.
	(d) Can form images of objects spread over a large area.

Answer:

Column I	Column II
(i) A plane mirror	(b) Image is erect & of the same size as of the object.
(ii) A concave mirror	(c) Used by dentists to see enlarged image of teeth.
(iii) A convex	(d) Can form image of objects spread over a large area.

Question 2.

Column I	Column II
(i) r > 90	(a) Light gazes the surface of separation between two mode.
(ii) r = 90	(b) No refraction.
(iii) r < 90	(c) Refracted ray away from the normal

Answer:

Column I	Column II
(i) r > 90	(b) No refraction.
(ii) r = 90	(a) Light gazes the surface of separation between two mode.
(iii) r < 90	(c) Refracted ray away from the normal

Question 3.

Column I	Column II
(i) plane mirror	(a) Focal length is positive.
(ii) concave	(b) Focal length is negative.
(iii) convex	(c) Focal length is infinity.
(iv) Real image	(d) Magnification if positive value.
(v) Virtual image	(e) Magnification if negative value.

Answer:

Column I	Column II
(i) plane mirror	(c) Focal length is infinity.
(ii) concave	(b) Focal length is negative.
(iii) convex	(a) Focal length is positive.
(iv) Real image	(e) Magnification if negative value.
(v) Virtual image	(d) Magnification if positive value.

Question 4.

Answer:

V. Assertion & Reason Type :

(a) If both assertion & reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion & reason are true but the reason is not correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If assertion & reason both are false.
(e) If assertion is false but reason is true.

Question 1.
Assertion : The air bubble shines in water.
Reason : Air bubble shines due to refraction of light.
Answer:
(c) If assertion is true but reason is false

Question 2.
Assertion : The focal length of the mirror is /and distance of the object from the
focus is V then the magnification of the mirror will be \(\left(\frac{f}{f-u}\right)\)

Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

Question 3.
Assertion : When an object is placed between two plane mirrors, then all the images found are of equal brightness.
Reason : Only two images are obtained in case of plane-parallel mirrors.
Answer:
(d) Assertion & reason both are false

Question 4.
Assertion: The mirrors used in torch lights are parabolic not concave.
Reason: The image formed by concave mirror is always virtual.
Answer:
(c) Assertion is true but reason is false

Question 5.
Assertion : The nature of the image depends on the size of the mirror.
Reason : Small mirrors always form a virtual image.
Answer:
(d) Assertion & reason both are false

Question 6.
Assertion : A real image cannot be produced by plane or convex mirror.
Reason : The focal length of a convex mirror is always taken as possitive.
Answer:
(e) Assertion is false but reason is true

VI. Answer very briefly :

Question 1.
Which is optically denser out of the two medium M₁& M₂ having the refractive indices = 1.71 and 1.36 respectively?
Answer:
M₁
Reason: Optical density increases as the value of the refractive index increases.

Question 2.
Two medium with refractive index 1.31 & 1.50 is given. In which case (i) Bending of light is more and (ii) speed of light is more.
Answer:
(i) 1.50 – Bending is more
(ii) 1.31 – Speed is more

Question 3.
Under what circumstances there won’t be any refraction of light when it enters from one medium to another?
Answer:

• When light incident at 90°, it will not bend.
• When light passes from denser medium to rarer medium and if it is incident at an angle greater than the critical angle, it will reflect but will not refract.

Question 4.
A ray of light traveling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
Answer:

• When a ray of light travels from air into water obliquely, it bends towards the normal.
• This is because water is optically denser than air.
• On entering water, speed of light decreases and the light bends towards normal.

Question 5.
List down the uses of concave mirror.
Answer:
Concave mirrors are used :

• As Shaving mirror.
• As Reflectors in automobile headlights & torches.
• By dentists to see large images of the teeth of patients.
• To produce heat in solar furnaces.

Question 6.
What are the characteristics of the image formed on a plane mirror?
Answer:

• Image is upright.
• Size of the image is the same as the size of the object.

Question 7.
State the laws of reflection of light.
Answer:

• The incident ray, the normal at the point of incidence and the reflected ray, all lie in the same plane.
• Angle of incidence is equal to the angle of reflection.

Question 8.
Describe the nature of images formed by plane mirrors.
Answer:

• It is always virtual and erect.
• Its size is equal to that of the object
• It is formed at the same distance behind the mirror as the object is in front of the mirror.
• It is laterally inverted.

Question 9.
What is lateral inversion in a plane mirror?
Answer:
It means the apparent reversal of left and right in the mirror image compared with the object.

Question 10.
Explain why a ray of light passing through the centre of curvature of a concave mirror, gets reflected along with the same pattern.
Answer:
The ray passing through the centre of curvature incident to the mirror along its normal so < i = < r = 0
∴ The ray retraces its pattern

Question 11.
How tall does a mirror have to be to fit an entire person’s body?
Answer:
The height of the mirror should behalf of the person’s height regardless of the distance of the person from the mirror.

Question 12.
What is concave and convex mirror?
Answer:

• If the reflecting surface is curved inwards that is called concave mirror.
• The reflecting surface is curved outwards, then it is called convex mirror.

Question 13.
Define principal focus of concave mirror.
Answer:
Principal focus (F): The point on the principal axis of the spherical mirror where the rays of light parallel to the principal axis meet or appear to meet after reflection from the spherical mirror.

Question 14.
What is focal length (f) of a mirror?
Answer:
The distance between the pole (P) and the principal focus (F) of the spherical mirror is called the focal length.
f = \(\frac { R }{ 2 }\) , where R is the radius of curvature of the mirror.

Question 15.
Define Radius of curvature.
Answer:
The radius of the hollow sphere of which the spherical mirror forms a part is called the radius of curvature (R)
R = 2 × focal length

Question 16.
What is “aperture”?
Answer:
The diameter of the circular rim of the mirror is called the aperture of the mirror. It is the entire area of the reflecting surface of the mirror.

Question 17.
Distinguish between real & virtual image.
Answer:
Real :

1. Light rays that come from an object actually meet after reflection.
2. It can be obtained on a screen
3. Image is inverted

Virtual :

1. Light comes from an object does not actually meet but appears to meet.
2. It cannot be obtained on the screen.
3. The image is erect.

Question 18.
What do you mean by linear magnification?
Answer:
It is defined as the ratio of the height of the image (h_i) to the height of the object (h_o).
\(m=\frac{h_{i}}{h_{o}}(\text { or }) \quad m=-\frac{v}{u}\)

Question 19.
Which kind of mirrors are used in the shaving mirror? Why?
Answer:
Cancave mirror, to get magnified image. When a cancave mirror is held near the face (between the pole and focus of the mirror) then an upright and magnified image is seen.

Question 20.
Which mirror is used as a reflector? Why?
Answer:

• Concave mirrors are used as reflectors in torches, vehicle headlights and searchlights.
• To get a powerful parallel beam of light.

Question 21.
Write the uses of cancave mirror
Answer:

1. As a shaving mirror: Magnified face will be seen
2. As a dentist head mirror: Focuses the lights on to see a small area of the body (teeth, throat, etc.)
3. As reflectors: To get a powerful beam of light
4. In solar heaters: To focus sun light for heaters

Question 22.
What do you observe when an object is placed anywhere between P and infinity in front of a convex mirror?
Answer:

• The image is formed behind the mirror between the pole (P) and focus (F).
• Virtual and erect image.
• Diminished image.

Question 23.
What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is +4?
Answer:
Positive sign of magnification indicates that image is virtual, erect and enlarged.

Question 24.
Between which two points of a concave mirror should an object be placed to obtain a magnification of -2?
Answer:
Negative sign of magnification indicates that image is real and inverted. Sign of image is magnified (enlarge)
∴ Object is placed between F and C.

Question 25.
To obtain an image twice the size of the object, between which two points related to a concave mirror should an object be placed?
Answer:
Between F (principal focus) and C centre of curvature.
Real Image.

Question 26.
Draw a ray diagram and also state the position the relative size and nature of image formed by a concave mirror, when an object is placed at C.
Answer:
Image Position: At C, itself
Size: Same size
Nature : (i) Real
(ii) Inverted

Question 27.
Why a pencil partly immersed in water appears to be bent at the water surface.
Answer:
The pencil dipped in water appears bent due to the refraction of light.
The angle of refraction depends on the refractive index of the medium.

Question 28.
How should a ray of light be incident on a rectangular glass slab so that it comes out from the opposite side of the slab without being displaced?
Answer:
Along the normal to the surface or at an angle of incidence of i = 0.

Question 29.
Why a convex mirror is preferred for rearview mirrors in cars?
Answer:

• It always forms virtual, erect, and diminished images.
• The field of view increases.

Question 30.
List four properties of the image formed by a convex mirror.
Answer:

• Always formed behind the mirror between P & F.
• Virtual & erect
• Size is always smaller than the object.
• Magnification is always positive.

Question 31.
List four properties of the image formed by the concave mirror when the object is placed between F & P
Answer:

• The image formed behind the mirror
• Enlarged
• Virtual
• Erect

Question 32.
What is meant by the refraction of light?
Answer:
Light does not travel in the same direction in all media. It changes its direction, the bending of a light ray when it passes from one medium to another is called refraction of light.

Question 33.
State the laws of refraction of light.
Answer:
(i) The incident ray, the refracted ray, and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.

(ii) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction.
If i is the angle of incidence and r is the angle of refraction, then \(\frac{\sin i}{\sin r}[latex] = constant
This constant is called the refractive index of the second medium with respect to the first medium. T

Question 34.
Define refractive index & write its unit.
Answer:
The refractive index of the second medium with respect to the first medium is defined as the ratio of the sine of the angle of incidence in the first medium to the sine of the angle of refraction in the second medium.
Unit: The refractive index has no unit as it is the ratio of two similar quantities

Question 35.
Define refractive index in terms of speed of light.
Answer:
The refractive index of a medium is also defined in terms of speed of light in different media

Question 36.
What is total internal reflection?
Answer:
Total internal reflection: When the angle of incidence exceeds the value of the critical angle, the refracted ray is not possible, since r > 90°, the ray is totally reflected back to the same medium (denser medium). This is called as total internal reflection.

Question 37.
Define the critical angle.
Answer:
The angle of incidence at which the angle of refraction is 90° is called the critical angle.

Question 38.
What are the conditions to achieve total internal reflection?
Answer:

• Light must travel from denser medium (Water) to rarer medium (Air).
• The angle of incidence inside the denser medium must be greater than that of the critical angle.

Question 39.
What is mirage? How it occurs?
Answer:

• Mirage is an optical illusion caused by the refraction of light from the sky by heated air.
• The air near the ground becomes hotter than the air at higher levels.
• The refractive index of air increases with its density. Hotter air is less dense, and has smaller refractive index than cooler air.
• If the air currents are small, that is, the air is still, the optical density of different layers of air increases with height.
• As a result, light from an object such as a car passes through a medium whose refractive index decreases towards the ground.
• Thus, a ray of light from such an object successively bends away from the normal and undergoes total internal reflection, if the angle of incidence for the air near the ground exceeds the critical angle.

Question 40.
How do twinkling stars occur? (or) what is the cause of the twinkling of stars?
Answer:
Refraction of light:

• Light from a star is refracted as it passes through our atmosphere because the light
  passes rapidly through moving cells of air with different densities, temperatures, etc.
• These cells bend light by different amounts and make the apparent position of the star move around. This movement is seen as twinkling.

Question 41.
What is the phenomenon used in optical fibre? Explain.
Answer:

• Optical fibres are extensively used for transmitting audio and video signals through long distances.
• Optical fibres too make use of the phenomenon of total internal reflection.
• Optical fibers are fabricated with high-quality composite glass/quartz fibres.
  Each fibres consists of a core and cladding. The refractive index of the material of the core is higher than that of the cladding.

When a signal in the form of light is directed at one end of the fibre at a suitable angle, it undergoes repeated total internal reflection along the length of the fibre and finally comes out at the other end. Optical fibres are extensively used for transmitting and receiving electrical signals which are converted to light between the ends of the fibre, over long distances.

Question 42.
Write any two uses of total internal reflection.
Answer:

1. Spectacular brilliance of diamonds.
2. Transmission of audio and video signals to long-distance through optical fibres.

Question 43.
What are the examples of total internal reflection in nature?
Answer:

1. Mirage
2. Twinkling of stars

Question 44.
Give two examples of the transparent medium that are denser than air.
Answer:
Water, glass.

Question 45.
A coin in a glass beaker appears to rise as the beaker is slowly filled with water why?
Answer:
Refraction of light at the air-water interface.

Question 46.
Name the spherical mirror(s) that has/have
(i) Virtual principal focus
(ii) Real principal focus
Answer:
(i) Convex
(ii) Concave.

VII. Long Answers

Question 1.
List the sign conventions for reflection of light by spherical mirrors.
(i) Write the formula for the spherical mirror.
(ii) Mirror Equation
Answer:

(i)

• The object is always placed on the left side of the mirror.
• All distances are measured from the pole of the mirror.
• Distances measured in the direction of light are taken as positive (along + X-axis) and those measured in the opposite direction are taken as negative (along – X-axis).
• All distances measured perpendicular to and above the principal axis (along + Y-axis) are considered to be positive.
• All distances measured perpendicular to and below the principal axis (along – Y-axis) are considered to be negative. Cartesian sign conventions are used to derive mirror formula and do simple calculations.

(ii) Mirror Equation
The expression relating the distance of the object u, a distance of image v, and focal length f of a spherical mirror is called the mirror equation.
[latex]\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)

f – focal length of a spherical mirror
u – Distance of the object
v – Distance of the image

Linear Magnification:

It can be defined as the ratio of the height of the image (h_i) to the height of the object (h_o)
m = \(\frac{h_{i}}{h_{o}}(\text { or }) \frac{-v}{u}\)
h_i = height of the image
h_o = height of the object

Question 2.
State the type of mirror used as
(i) Convex mirror
(ii) Concave mirror
Answer:
(i) Convex mirror :

• It gives a wide field of view
• It produces erect and small size image of the object. [As the vehicles approach the driver from behind, the size of the image increases. When vehicles are moving away from the driver, the image size decreases]

(ii) Concave mirror:
To see a large size image of the face.
When the object lies in between pole and principal focus, it forms a virtual, erect and enlarged image.

Question 3.
Write the rules for the construction of image by Concave mirrors, along with ray diagram. .
Answer:
(i) Rule 1 : A ray passing through the centre of curvature is reflected back along its own path.

(ii) Rule 2 : A ray parallel to the principal axis passes through the focus after reflection.

(iii) Rule 3 :A ray passing through the focus gets reflected and travels parallel to the principal axis.

(iv) Rule 4 : A ray AP incident at the pole of the mirror gets reflected along a path PB
such that the angle of incidence APC is equal to the angle of reflection BPC.

Question 4.
Describe the nature and location of the images for the different positions of object which is placed in front of the concave mirror.
Answer:

VIII. Higher-Order Thinking Skills :

Question 1.
M = 2.42 for diamond. What is the meaning of this statement in relation to the speed of light?
Answer:
It means that light travels 2.42 times faster in a vacuum than in a diamond.

Question 2.
A convex mirror is in water. What should be the change in its focal length?
Answer:
No change. The focal length of a convex mirror does not depend on the nature of the medium.

Question 3.
Are the laws of reflection true in the case of irregular reflection?
Answer:
Yes, at the point of incidence both laws of reflection will hold good.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 2 Motion Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 2 Motion

9th Science Guide Motion Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
The area under velocity – time graph represents the
(a) velocity of the moving object.
(b) displacement covered by the moving object,
(c) speed of the moving object.
(d) acceleration of the moving object.
Answer:
(b) displacement covered by the moving object

Question 2.
Which one of the following is most likely not a case of uniform circular motion?
(a) Motion of the Earth around the Sim.
(b) Motion of a toy train on a circular track.
(c) Motion of a racing car on a circular track.
(d) Motion of hours’ hand on the dial of the clock.
Answer:
(c) Motion of a racing car on a circular track

Question 3.
Which of the following graph represents uniform motion of a moving particle?


Answer:

Question 4.
The centrifugal force is
(a) a real force.
(b) the force of reaction of centripetal force.
(c) a virtual force.
(d) directed towards the centre of the circular path.
Answer:
(c) a virtual force

II. Fill in the blanks :

1. Speed is a …………………….quantity whereas velocity is a …………….quantity.
Answer:
Scalar, Vector

2. The slope of the distance – time graph at any point gives ………………
Answer:
Speed

3. Negative acceleration is called ……………………
Answer:
retardation (or) deceleration

4. Area under velocity – time graph shows ……………………………….
Answer:
displacement

III. State whether true or false. If false, correct the statement:

1. The motion of a city bus in a heavy traffic road is an example for uniform motion.
Answer:
False.
Correct statement: The motion of a city bus in a heavy traffic road is an example for non-uniform motion.

2. Acceleration can get negative value also.
Answer:
True.

3. Distance covered by a particle never becomes zero but displacement becomes zero.
Answer:
True.

4. The velocity – time graph of a particle falling freely under gravity would be a straight line parallel to the x axis. .
Answer:
False.
Correct statement: The velocity – time graph of aparticle moving at uniform do dry. would be straight line parallel to the x axis.

5. If the velocity – time graph of a particle is a straight line inclined to X-axis then its displacement – time graph will be a straight line.
Answer:
True.

IV. Assertion and Reason Type Questions :

Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion : The accelerated motion of an object may be due to change in magnitude of velocity or direction or both of them..
Reason : Acceleration can be produced only by change in magnitude of the velocity. It does not depend the direction.
Answer:
(c) If assertion is true but reason is false.

Question 2.
Assertion : The Speedometer of a car or a motor-cycle measures its average speed.
Reason : Average velocity is equal to total displacement divided by total time taken.
Answer:
(d) Assertion is false but reason is true

Question 3.
Assertion : Displacement of a body may be zero when distance travelled by it is not zero.
Reason : The displacement is the shortest distance between initial and final position.
Answer:
(a) Both assertion and reason are true and reason is the correct explanation of assertion

V. Match the Following :

Answer:

VI. Answer briefly :

Question 1.
Define velocity.
Answer:
Velocity is the rate of change of displacement. It. is the displacement in unit time.

Question 2.
Distinguish distance and displacement.
Answer:
Table
Distance

1. The actual length of the path travelled by a moving body irrespective of the direction
2. It is a Scalar quantity

Displacement:

1. The change in position of a moving body in a particular direction
2. It is a Vector quantity

Question 3.
What do you mean by uniform-motion?
Answer:
An object is said to be in uniform motion if it covers equal distances in equal intervals of time how so ever big or small these time intervals may be.

Question 4.
Compare speed and velocity.
Answer:

Speed	Velocity
1. It is the rate of change of distance with respect to time	It is the rate of change of displacement with respect to time
2. It is a scalar quantity having magnitude only	It is a vector quantity having both magnitude and direction
3. Speed is velocity without a particular direction	Velocity is speed in a particular direction
4. It is measured in ms-1 in SI system	It is also measured in ms-1 in a particular direction in SI system
5. Speed in any direction would be a positive quantify, since the distance in any direction is a positive quantity.	Velocity can get both positive and negative values. If velocity in one direction is assumed to be positive then the velocity in the opposite direction would be a negative quantity. Velocity can get zero value also.

Question 5.
What do you understand about negative acceleration?
Answer:
If v < u, i.e. if final velocity is less than initial velocity, the velocity decreases with time and the value of acceleration is negative. It is called negative acceleration. It is also called as retardation (or) deceleration.

Question 6.
Is the uniform circular motion accelerated? Give reasons for your answer.
Answer: When an object is moving with a constant speed along a circular path, the change in velocity is only due to the change in direction. Hence it is accelerated motion.

Question 7.
What is meant by uniform circular motion? Give two examples of uniform circular motion.
Answer:
When an object moves with constant speed along a circular path, the motion is called uniform circular motion.
Example :

• The earth moves around the sun in the uniform circular motion.
• The moon moves in uniform circular motion around the earth.

VII. Answer in detail :

Question 1.
Derive the equations of motion by graphical method.
Answer:
Equations of motion from velocity-time graph:

Graph shows the change in velocity with time of a uniformly accelerated object. The object starts from the point D in the graph with velocity u. Its velocity keeps increasing and after time t it reaches the point B on the graph.
The initial velocity of the object = u = OD = EA
The final velocity of the object = v = OC = EB
Time = t = OE = DA
Also from the graph we know that, AB = DC

1. First equation of motion :

By definition, acceleration = change in velocity / time
= (final velocity – initial velocity)/time
= (OC – OD) / OE
= DC / OE
a = DC /t
DC = AB = at
From the graph EB = EA + AB
v = u + at…………..(1)
This is first equation of motion. .

2. Second equation on of motion :
From the graph the distance covered by the object during time t is given by the area of quadrangle DOEB

s = area of the quadrangle DOEB
= area of the rectangle DOEA + area of the triangle DAB
= (AE x OE) + (1/2 × AB × DA) .
s = ut + 1/2 (at²) …………(2)
This is the second equation of motion.

3. Third equation of motion :
From the graph the distance covered by the object during time, t is given by the area of the quadrangle DOEB. Here DOEB is a trapezium. Then,
s = area of trapezium DOEB
= 1/2 × sum of length of parallel side × distance between parallel sides
= 1/2 × (OD + BE) × OE
S = 1/2 ×× (u + v) × t
since a = (v – u) /1 or t = (v – u) / a
Therefore s = 1/2 × (v + u) x (v – u) / a
2as = v² – u²
v² = u² + 2 as …………….. (3)
This is the third equation of motion.

Question 2.
Explain different types of motion.
Answer:
In physics, motion can be classified as below.

1. Linear motion: Motion along a straight line.

2. Circular motion: Motion along a circular path.

3. Oscillatory motion: Repetitive to and fro motion of an object at regular intervals of time. Random motion: Motion of the object which does not fall in any of the above categories.

Uniform and Non-uniform motion:

Uniform motion: Consider a car that covers 60 km in the first hour, 60 km in the second horn-, and another 60 km in the third hour, and so on. The car covers equal distance at equal intervals of time. We can say that the motion of the car is uniform. An object is said to be in uniform motion if it covers equal distances in equal intervals of time howsoever big or small these time intervals may be.

Non-uniform motion: Now, consider a bus starting from one stop. It proceeds slowly when it passes through a crowded area of the road. Suppose, it manages to travel merely 100 m in 5 minutes due to heavy traffic and is able to travel about 2 km in 5 minutes when the road is clear. Hence, the motion of the bus is non-uniform i.e. it travels unequal distances in equal intervals of time.

VIII. Exercise Problems:

Question 1.
A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10ms^-2, with what velocity will it strike the ground? After what time will it strike the ground?
Answer:
Here we have
Initial velocity, u = 0
Distance, s = 20 m
Acceleration, a = 10 m/s²
Final velocity, v = ?
Time, t = ?

a) Calculation of final velocity, v
We know that, v² = u² + 2as
v² = 0 + 2 × 10m/s² × 20m
v² = 400m²/s²
\(=\sqrt{400 m^{2} / s^{2}}\)
v = 20m/s

b) Calculation of time, t
We know that, v = u + at
20 m/s = 0 + 10m/s² × t
t = \(\frac{20 m / s^{2}}{20 m / s}=2 s\)
∴ Ball will strike the ground at a velocity of 20 ms^-1
Time taken to reach the ground = 2s.

Question 2.
An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 m and 20 s?
Answer:
Here we have
Diameter = 200. m
∴ Radius = 200 m/2 = 100 m
Time of one rotation = 40 s
Time after 2m 20 s = 2 × 60 s +20 s = 140 s
Distance after 140 s = ?
Displacement after 140 s = ?
Circular track with a diameter of 200m
We know that, velocity

a) Distance after 140 s
We know that, distance = velocity × time
= Distance 15.7 rn/s × 140 s
= 2198m

b) Displacement after 2 min 20 s i.e, in 140 s
We know that, distance = velocity × time
Since, rotation in 40 s = 1
∴ Rotation in 1 s = \(\frac{1}{40}\)
∴ Rotation in 140 s = \(\frac{1}{40} \times 140=3.5\)
∴ In 3.5 rotation athlete will be just at the opposite side of the circular track,
i.e. at a distance equal to the diameter of the circular track which is equal to 200m
∴ Distance covered in 2min 20 s = 2198 m
Displacement after 2min 20 5 = 200 m.

Question 3.
A racing car has a uniform acceleration of 4ms-2. What distance it covers in 10s after the start?
Answer:
Here we have
Acceleration, a = 4 m/s².
Initial velocity u = 0
Time t = 10 s
Distance (s) covered =?
We know that, s = ut + \(\frac { 1 }{ 2 }\) at²
s = (0 × 10s) + [\(\frac { 1 }{ 2 }\) × 4 m/s² × (10 s)²]
= \(\frac { 1 }{ 2 }\) × 4 m/s² × 100 s²
= 2 × 100 m = 200 m

Thus, racing car will cover a distance of 200 m after start in 10s with given acceleration.

Intex Activities

ACTIVITY – 1

Look around you. You can see many things: a row of houses, large trees, small plants, flying birds, running cars and many more. List the objects which remain fixed at their position and the objects which keep on changing their position.
Solution:

1. Row of houses, large trees, small plants are the examples, of immovable objects.
2. Flying birds, running cars and buses are the examples of movable objects.

Activity to be done by the students themselves

ACTIVITY – 2

Tabulate the distance covered by a bus in a heavy traffic road in equal intervals of time and do the same for a train which is not in an accelerated motion. From your table what do you understand?
The bus covers unequal distance in equal intervals of time but the train covers equal distances in equal intervals of time.
Solution:

ACTIVITY – 3

Observe the motion of a car as shown in the figure and answer the following questions:
Compare the distance covered by the car through the path ABC and AC. What do you observe? Which path gives the shortest distance to reach D from A? Is it the path ABCD or the path ACD or the path AD?

Solution:

1. Distance covered by the car through the path ABC = 4m + 3m = 7 m. and AC = 5 m. The distance covered by the car through the path ABC is large compared to AC.
2. The shortest distance to resell D from A is path AD = 3m.
3. The total distance covered by the car ABCD A = 14 m. It finally reaches to A.

ACTIVITY – 4

Take a large stone and a small eraser. Stand on the top fit a table and drop them simultaneously from the same height? What do you observe? Now, take a small eraser and a sheet of paper. Drop them simultaneously from the same height. What do you observe? This time, take two sheets of paper having same mass and crumple one of the sheets into a ball. Now, drop the sheet and the ball from the same height. What do you observe?
Solution :
Both the stone and the eraser have reached the surface of the earth almost at the same time.
The eraser reaches first and the sheet of paper reaches later.
The paper crumpled into a ball reaches ground first and plain sheet of paper reaches later, although they have equal mass. It is because of air resistance. The magnitude of air resistance despends on the area of object exposed to air. So the sheet of paper reaches later.

9th Science Guide Motion Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
A particle is moving in a circular pattern of radius r. The displacement after half a circle would be
(a) zero
(b) πr
(c) 2r
(d) 2πr
Answer:
(c) 2r

Question 2.
In which of the following cases of motions, the distance moved and the magnitude of displacement are equal?
(a) If the car is moving in the straight road.
(b) If the car is moving in a circular road.
(c) The earth is revolving around the sun.
(d) The pendulum is moving to and fro
Answer:
(a) If the car is moving in the straight road

Question 3.
A body is thrown vertically upward with velocity, the greatest height h to which it will rise is
(a) u²/2g
(b) u²/g
(c) u/g
(d) u/2g
Answer:
(a) u²/2g

Question 4.
If the displacement of an object is proportional to square of time, then the object moves with
(a) uniform velocity
(b) uniform acceleration
(c) increasing acceleration
(d) decreasing acceleration
Answer:
(b) uniform acceleration

Question 5.
From the given v-t graph, u can be inferred that the object is
(a) in uniform motion
(b) at rest
(c) in non-uniform motion
(d) moving with uniform acceleration
Answer:
(a) in uniform motion

Question 6.
The area under v-t graph represents a physical quantity which has the unit.
(a) m²
(b) m
(c) m³
(d) ms^-1
Answer:
(b) m

Question 7.
m/s² is the unit of
(a) distance
(b) displacement
(c) velocity
(d) acceleration
Answer:
(d) acceleration

Question 8.
The rate of change of displacement
(a) speed
(b) velocity
(c) acceleration
(d) retardation
Answer:
(b) velocity

Question 9.
A scalar quantity has T
(a) magnitude only
(b) direction only
(c) both
(d) none
Answer:
(a) magnitude only

Question 10.
When an object undergoes acceleration
(a) there is always an increase in its velocity
(b) there is always an increase in its speed
(c) a force always acting on it.
(d) all of the above
Answer:
(c) a force always acting on it

Question 11.
A body is projected up with an initial velocity u m/s. It goes up to a height, ‘h’ metres in seconds time. Then it comes back at the point of projection. Considering negligible air resistance, which of the following statement is true?
(a) the acceleration is zero
(b) the displacement is zero
(c) the average velocity is 2hit
(d) the final velocity is 2u when body reaches projection point
Answer:
(b) the displacement is zero

Question 12.
A car accelerates at 1.5m/s²in a straight road. How much is the increase in velocity in 4s.
(a) 6 m/s
(b) 4 m/s
(c) 3 m/s
(d) 2.66 m/s
Answer:
(a) 6 m/s

Question 13.
The slope of the distance-time curve is steeper / greater is the
(a) velocity
(b) acceleration
(c) displacement
(d) speed
Answer:
(d) speed

Question 14.
The given graph represents motion with …………….speed.

(a) uniform
(b) non-uniform
(c) constant
(d) none
Answer:
(b) non-uniform

Question 15.
The relation between displacemeñt and time is given by the equation of
(a) v² = ut + at
(b) s = ut + \(\frac { 1 }{ 2 }\) at²
(e) c = s/t
(d) v² = u² + 2as
Answer:
(b) s = ut + \(\frac { 1 }{ 2 }\) at²

Question 16.
A body moves in a uniform circular motion
(a) It is moving with constant velocity
(b) its acceleration is zero
(c) the body has an acceleration y
(d) none of the above
Answer:
(a) It is moving with constant velocity

Question 17.
Speed of the body in particular direction can be called
(a) acceleration
(b) displacement
(c) velocity
(d) distance
Answer:
(c) velocity

Question 18.
Statement A: Uniform circular motion is a case of accelerated motion
Statement B: In third equation of motion we do not have the term time
(a) Statement B is true, A is false
(b) Statement A is true, B is false
(c) neither statement A nor B is true
(d) both are true
Answer:
(d) both are true

Question 19.
Which of the following is correct about uniform circular motion
(i) direction of motion is continuously changed
(ii) direction of motion is not changed
(iii) speed and direction both remain constant
(iv) speed is constant but direction is changing
(a) ii & iii are correct
(b) i, ii & iii are correct
(c) i & iv are correct
(d) all of these
Answer:
(c) i & iv are correct

Question 20.
Which of the quantities have the same SI unit?
(a) speed, velocity
(b) acceleration, time
(c) velocity, time
(d) velocity, acceleration
Answer:
(a) speed, velocity

Question 21.
Rest and motion of body are
(a) non-relative
(b) not related
(c) relative
(d) none
Answer:
(c) relative

Question 22.
An ant moves from one corner of a room diagonally to the opposite corner. If the dimensions of the hall are 8m x 6m, the displacement of the ant is
(a) 10m
(b) 14m
(c) 28m
(d) 2m
Answer:
(a) 10m

Question 23.
The displacement covered by a second hand of radius V in a clock after one revolution is
(a) 360°
(b) 0
(c) 3r
(d) 2r
Answer:
(b) 0

Question 24.
A man leaves his house at 6.30 a.m. for a morning walk and returns back at 7.30 a.m. after covering 4 km. Displacement covered by him is …………….
(a) 2 km
(b) zero
(c) 8 km
(d) 4 km
Answer:
(b) zero

Question 25.
A body is said to be in non uniform motion if it travels
(a) equal distance in unequal interval of time
(b) equal distance in equal interval of time
(c) unequal distance in unequal interval of time
(d) unequal distance in equal interval of time.
Answer:
(d) unequal distance in equal interval of time

Question 26.
A quantity which has both magnitude and direction is
(a) scalar
(b) distant
(c) vector
(d) moving body
Answer:
(c) vector

Question 27.
A bus accelerating with 4ms-2 changes its speed from 60ms_1 to a certain value in 5s. The final speed is
(a) 40 m/s
(b) 25 ms^-1
(c) 60 ms^-1
(d) 30 ms^-1
Answer:
(a) 40 m/s

Question 28.
A quantity has a value of 16ms-2. It is the
(a) acceleration of an object
(b) velocity of an object
(c) retardation of an object
(d) speed of an object
Answer:
(c) retardation of an object

Question 29.
A boy throws a ball up and catches it when the ball falls back. In which part of the motion the ball is accelerating?
(a) during downward motion
(b) when the ball comes to rest
(c) during upward motion
(d) when the boy catches the ball.
Answer:
(a) during downward motion]

Question 30.
Choose the correct option.
(a) distance is a scalar, velocity is a vector, acceleration is a vector
(b) distance is a vector, velocity is a scalar, acceleration is a vector
(c) distance is a vector, velocity is a vector, acceleration is a vector
(d) distance is a scalar, velocity is a vector, acceleration is scalar
Answer:
(a) distance is a scalar, velocity is a vector, acceleration is a vector

Question 31.
If a moving body comes to rest, then its acceleration is
(a) positive
(b) negative
(c) zero
(d) all of these depending upon initial velocity.
Answer:
(b) negative

Question 32.
If the velocity of a body changes uniformly from u to v in time t, the sum of average velocity and acceleration is


Answer:

Question 33.
Acceleration is defined as the rate of change of
(a) distance
(b) velocity
(c) speed
(d) displacement
Answer:
(b) velocity

Question 34.
When an object undergoes acceleration
(a) there is always an increase in its velocity ‘
(b) there is always an increase in its speed
(c) a force always acting on it.
(d) all the above
Answer:
(c) a force always acting on it

Question 35.
The equation v = u + at gives information as
(a) velocity is a function of time
(b) velocity is a function of position
(c) position is a function of time
(d) position is a function of time and velocity
Answer:
(a) velocity is a function of time

Question 36.
Which of the following can determine the acceleration of a moving object.
(a) area of the velocity-time graph
(b) the slope of the velocity-time graph
(c) area of a distance-time graph
(d) the slope of a distance-time graph
Answer:
(b) slope of the velocity-time graph

Question 37.
What is the slope of the body when it moves with uniform velocity?
(a) positive
(b) negative
(c) zero
(d) may be positive or negative
Answer:
(c) zero]

Question 38.
If a body starts from rest, what can be said about the acceleration of the body?
(a) positively accelerated
(b) negative accelerated
(c) uniform accelerated
(d) none of the above
Answer:
(a) positively accelerated

Question 39.
When a body moves uniformly along the circle then
(a) its velocity changes but speed remain the same
(b) its speed changes but velocity remains the same
(c) both speed and velocity changes
(d) both speed and velocity remains same
Answer:
(a) its velocity changes but speed remains the same

Question 40.
Distance travelled by a freely falling body is proportional to
(a) mass of the body
(b) square of the acceleration due to gravity
(c) square of the time of fall
(d) time of fall
Answer:
(c) square of the time of fall

Question 41.
If the displacement-time graph of a particle is parallel to the time axis, then velocity of the particle is.
(a) infinity
(b) unity
(c) equal to acceleration
(d) zero
Answer:
(d) zero

Question 42.
In the velocity-time graph, AB shows that the body has

(a) uniform acceleration
(b) non-uniform retardation
(c) uniform speed
(d) initial velocity OA & is moving with uniform retardation.
Answer:
(d) initial velocity OA & is moving with uniform retardation

Question 43.
The magnitude of the centripetal force is given by (F= ….)


Answer:

Question 44.
A body moving with an initial velocity 5ms^-1 and accelerates at 2ms ^-2. Its velocity after 10s is
(a) 20ms^-1
(b) 25ms^-1
(c) 5ms^-1
(d) 22.55ms^-1
Answer:
(b) 25ms^-1

Question 45.
In a 100m race, the winner takes 10s to reach the finishing point. The average speed of the winner is
(a) 5ms^-1
b) 20ms^-1
c) 40ms^-1
d) 10ms^-1
Answer:
(d) 10ms^-2

Question 46.
The area under the velocity-time graph represents
(a) the velocity of the moving object
(b) displacement covered by the moving object
(c) speed of the moving object.
(d) acceleration of the moving object
Answer:
(b) displacement covered by the moving object

Question 47.
A car is being driven at a speed of 20ms^-1 when brakes are applied to bring it to rest in 5 s. The deceleration produced in this case will be
(a) +4ms^-2
(b) -4ms^-2
(c) -0.25ms^-2
(d) +0.25ms^-2
Answer:
(b) -4ms^-2

Question 48.
Unit of acceleration is
(a) ms^-1
(b) ms^-2
(c) ms
(d) ms²
Answer:
(b) ms^-2

Question 49.
The force responsible for drying clothes in a washing machine is …………….
(a) Centripetal force
(b) Centrifugal force
(c) Gravitational force
(d) Electro static force
Answer:
(b) Centrifugal force

II. Fill in the blanks:

1. If a body does not change its position, then it is said to be at …………………
Answer:
rest

2. The back and forth motion of a swing is an ………………… motion.
Answer:
Oscillatory

3. In uniform motion an object travels equal ………………… in ………………… interval of time.
Answer:
distances, equal

4. The actual path covered by a body is called …………………
Answer:
distance

5. Displacement is the ………………… distance covered by a body.
Answer:
shortest

6. The motion of the bus is ………………… motion.
Answer:
non-uniform

7. Rate of change of displacement is …………………
Answer:
velocity

8. Speed is a ………………… quantity whereas velocity is a …………………
Answer:
scalar, vector

9. If final velocity is less than initial velocity the acceleration is ………………….
Answer:
negative

10. If final velocity is equal to initial velocity the value of acceleration is ………………….
Answer:
zero

11. The slope of the distance-time graph becomes steeper & steeper the speed ………………….
Answer:
increases

12. A straight line parallel to the x-axis in the velocity-time graph, represents the object moves in…………………
Answer:
uniform velocity

13. From v-t graph ………………… can be calculated.
Answer:
displacement

14. ………………… measures the instantaneous speed of the automobile.
Answer:
Speedometer

15. Slope of the velocity-time graph gives…………………
Answer:
acceleration

16. The value of acceleration for a body at rest is…………………
Answer:
zero

17. At the highest point, when a body is thrown vertically upwards, the velocity is ………………….
Answer:
zero

18. A body moves in a circular pattern the ………………… of velocity does not change but changes.
Answer:
magnitude, direction

19. When a body moves in a circular pattern ………………… acceleration is directed radially towards the centre of the circle.
Answer:
centripetal

20. The separation of cream from milk-hn example for the application of ………………….
Answer:
centrifugal

21. Consider an object is rest at position x = 20m. Then its displacement – time graph will be straight-line ………………… to the time axis.
Answer:
Parallel

III. State whether true or false. If false, correct the statement:

1. Displacement can be zero but distance never.
Answer:
True.

2. Time is a vector quantity.
Answer:
False.
Correct statement: Time is a scalar quantity.

3. Displacement magnitude can be greater than the distance travelled by the object.
Answer:
True.

4. If the velocity of the body decreases with time the acceleration is negative and the motion is called decelerated motion.
Answer:
True.

5. Acceleration is a scalar.
Answer:
False.
Correct statement: Acceleration is a vector.

6. The area of the velocity-time graph gives the displacement of the body.
Answer:
True.

7. Motion & rest are relative terms.
Answer:
True.

8. An object can be moving with uniform speed but variable acceleration.
Answer:
True.

9. Slope of the distance-time graph indicates the speed.
Answer:
True.

10. It is possible to have object moving with uniform velocity but non-uniform acceleration.
Answer:
True.

11. It is possible to have object moving with uniform speed but variable acceleration.
Answer:
False.
Correct statement : It is possible to have object moving with uniform speed but constant acceleration.

12. The force experienced by a boy in the merry-go-round is a centripetal force.
Answer:
False.
Correct statement: The force experienced by a boy in the merry-go-round is a centrifugal force.

13. The initial velocity of a freely falling object is zero as it is released from rest.
Answer:
True.

IV. Assertion and Reason Type Questions :

(a) If both assertion & reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion & reason are true but the reason is not correct explanation of the assertion.
(c) If the assertion is true but the reason is false.
(d) If assertion & reason both are false.
(e) If assertion is false but reason is true.

Question 1.
Assertion : A body can have acceleration even if its velocity is zero at a given instant of time.
Reason: A body is momentarily at rest when it reverses its direction of motion.
Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

Question 2.
Assertion : If the displacement of the body is zero, the distance covered by it may not be zero.
Reason: Displacement is a vector & distance is a scalar quantity.
Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

Question 3.
Assertion: An object can have constant speed but the variable velocity
Reason: Speed is a scalar but velocity is a vector.
Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

Question 4.
Assertion: The speed of a body can be Negative.
Reason : If the body is moving in the opposite direction of positive motion, then its speed is Negative.
Answer:
(d) Assertion & reason both are false

Question 5.
Assertion : The position-time graph of a uniform motion in one dimension of a body can have Negative slope
Reason : When the speed of body decreases with time then, position-time graph of the moving body has Negative slope.
[Answer:
(c) Assertion is true but the reason is false

Question 6.
Assertion: A positive acceleration of a body can be associated with slowing down of the body.
Reason: Acceleration is a vector.
[Answer: (b) Both assertion & reason are true but the reason is not correct explanation of the assertion]

Question 7.
Assertion :A negative acceleration of a body can be associated with speeding up of the body.
Reason: Increase in speed of a moving body is independent of its direction of motion.
Answer:
(b) Both assertion & reason are true but the reason is not the correct explanation of the assertion

Question 8.
Assertion When a body is subjected to a uniform acceleration, it is always moving in a straight line.
Reason: Motion may be straight-line motion or circular motion.
Answer:
(e) Assertion is false but the reason is true

Question 9.
Assertion : Position-time graph of a stationary object is a straight line parallel to time axis. ’
Reason : For a stationary object, position does not change with time.
Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

Question 10.
Assertion : The slope of distance-time graph of a body moving with high speed is steeper than slope of distance-time graph of a body with low velocity.
Reason: Slope of distance-time graph = speed of the body.
Answer:
(a) Both assertion & reason are true and the reason is the correct explanation of the assertion

V. Answer briefly :

Question 1.
What are centripetal acceleration and centripetal force?
Answer:
When a body moves in a circular pattern the acceleration is directed radially towards the centre of the circle.
The force causing this acceleration is also directed towards the centre of the circle and it is called centripetal force.

Question 2.
Find the magnitude of centripetal force.
Answer:
Consider an object of mass m, moving along a circular path of radius r, with a velocity v, its centripetal acceleration is given by a = v² / r
Hence, the magnitude of centripetal force is given by,
F = mass x centripetal acceleration
F = mv² / r

Question 3.
What is centrifugal force? Give examples.
Answer:
Force acting on a body away from the centre of circular path is called centrifugal force. Thus centrifugal force is in a direction opposite to the direction of centripetal force. Its magnitude is same as that of centripetal force.
Example : Spin dryer of a washing machine, ride on a merry-go-round.

Question 4.
When an object is thrown upwards, what is true of velocity and acceleration at the highest point of motion of the object?
Answer:

• Velocity becomes zero
• Acceleration remains same as g.

Question 5.
Name the two quantities, the slope of whose graph gives (i) speed (ii) acceleration.
Answer:
(i) Distance – Time
(ii) Speed – Time

Question 6.
Define Average speed.
Answer:
It is the total distance travelled divided by the total time taken to cover this distance.

Question 7.
What do you infer if
(i) Distance – time graph is straight line.
(ii) Velocity time graph is curved.
(iii) Displacement time is zig zag.
Answer:
(i) Speed is constant.
(ii) Acceleration is not uniform.
(iii) Non uniform velocity.

Question 8.
Give the formula for each.
(i) Relation between initial, final velocity, acceleration and displacement in a uniformly accelerated straight line motion.
(ii) Relation between initial, final velocity, acceleration & time in a uniformly accelerated straight line motion.
(iii) Relation between initial velocity, acceleration, displacement and time.
Answer:
(i) Relation between initial, final Velocity, acceleration & displacement
in a uniformly accelerated straight line motion. v² = u² + 2as
(ii) Relation between initial, final velocity, acceleration & time
in a uniformly accelerated straight line motion. v = u + at
(iii) Relation between initial velocity, acceleration, displacement and time. s = ut+ 1/2 at²

Question 9.
What is the difference between uniform acceleration and non – uniform acceleration?
Answer:
Uniform Acceleration

1. It is the acceleration in which the object changes its velocity with equal intervals of time.
2. eg. The motion of a ball rolling down.

Non – Uniform Acceleration

1. It is the acceleration in which the object changes its velocity with unequal intervals of time.
2. A car travels 2 km in 1st hour, 3 km in 2nd hour and 3.5 km in 3rd horn.

Question 11.
Define Acceleration.
Answer:
Acceleration is the rate of change of velocity with respect to time or it is the rate of change of velocity in unit time. It is a vector quantity. The SI unit of acceleration is

VI. Paragraph Questions :

Question 1.
Define acceleration and state its SI unit for motion along a straight line, when do we consider the acceleration to be (i) positive (ii) negative? Give an example of a body in uniform acceleration.
Answer:
Answer: Acceleration is the rate of change of velocity with respect to time or it is the rate of change of velocity in unit time. It is a vector quantity. The SI unit of acceleration is ms^-2
Acceleration = Change in velocity/time
= (Final velocity – initial velocity)/time
a = \(\frac{v-u}{t}\)

If v > u, then ‘a’ is positive. If final velocity is greater than initial velocity, the velocity increase with time, the value of acceleration is positive.

If v < u, then a is negative. If final velocity is less than initial velocity
Example : The motion of a freely falling body and vertically thrown up body are the examples of uniform acceleration.
The motion of ball rolling down on an inclined plane is another example.

Question 2.
Distinguish between uniform motion and non
Answer:
uniform motion.

1. An object is said to be in uniform motion if it covers equkl distances in equal intervals of time.
2. example of uniform motion ‘train’

non-uniform motion.

1. If a body covers unequal distances in equal interval of time (or) equal distances in a different interval of time
2. example of non – uniform motion ‘bus’

Question 3.
Define uniform circular motion and give an example of it. Why is it called accelerated motion?
Answer:
When an object is moving with a constant speed along a circular path, the change in velocity is only due to the change in direction. Hence it is accelerated motion. Example:

1. The earth moves around the sun in a uniform circular motion.
2. The moon moves in uniform circular motion around the earth.

Question 4.
When a body is said to be in (i) uniform acceleration (ii) non – uniform acceleration?
Answer:
(i) A body is said to be in uniform acceleration if it travels in a straight line and its velocity increases or decreases by equal amounts in equal time intervals.
(ii) A body is said to be in non-uniform acceleration if the rate of change of its velocity is not constant i.e. differs in different time intervals.

Question 5.
What remains constant in uniform circular motion? And what changes continuously in uniform circular motion?
Answer:

• Speed remains constant in a uniform circular motion.
• Velocity changes continuously in a uniform circular motion.

Problems

Question 1.
A bus speed decreases from 50 km/h to 40 km/h in 3s, find the acceleration of the bus.
Answer:

Question 2.
A car starting from rest moves with uniform acceleration of 0.2 ms-2 for 3 min. Fine the (a) speed acquired (b) the distance travelled.
Answer:
Initial speed (u) = 0 m/s
Acceleration (a) = 0.2 ms^-2
Time taken (t) = 3 min = 3 × 60 = 180 s
Final velocity (v) = ?
Distance covered(s) = ?
v = u + at = 0 + 0.2 × 180 = 36 m/s
v = 36m/s
s = ut + 1/2 at² = 0 + 1/2 × 0.2 × (180)²
= 0.1 × 32400 = 3240 m
s = 3240m

Question 3.
A train is travelling at a speed of 90 kmh^-1. Brakes are applied so as to produce a uniform acceleration of-0.5 ms^-2, find how far the train will go before it is brought to rest.
Answer:
Initial velocity of train (u) = 90 km/h = \(\frac{90,000 \mathrm{~m}}{3,600 \mathrm{sec}}=25 \mathrm{~ms}^{-1}\)
Final velocity (v) = 0 ms^-1
Acceleration (a) = – 0.5 ms^-2
v² = u²+ 2as
s = (v² – u²) / 2a = (0² – 25²) / -(2 × 0.5)
s = -625/-1 = 625m
s = 625m

Question 4.
In a long-distance race the athletes were expected to take four rounds of the track such that the line of finish was same as the line of start. Suppose the length of the track was 300m,

(i) What is the total distance to be covered by the athletes?
What is the total displacement of the athletes when they touch the finish line?
(iii) Is the motion of the athletes uniform or non- D .^starting point uniform?
(iv) Is the displacement & distance moved by an athlete at the end of the race equal?
Answer:
(i) Total distance covered = 4 × 300 = 1200 m
(ii) Displacement = 0 [final position – initial position]
(iii) Non – uniform.
∵ the direction of motion is changing while running on the track.
(iv) Both are not equal.

Question 5.
Ram swims in a 80m long swimming pool. He covers 160m in 1 min by swimming from one end to the other and back along the same straight pattern. Find the average speed and average velocity.
Answer:
Total distance = 160m
Total displacement = 0
Time taken (t) = 1 min = 60s

Question 6.
Abus from Chennai travels to Trichy passes loo km, 160 km at 10.15 am, 11.15 am respectively. Find the average speed of the bus during 10.15 – 11.15 am.
Answer:
The distance coveredbetween 10.l5am& 11.15 am = 160 – 100
= 60km
The time interval = 1 h
Average speed = 60/1
= 60km/h

Question 7.
In a distance-time graph of two objects A & B, which object is moving with greater speed when both are moving?
Answer:
Object B makes a longer angle with the time – axis. Its slope is greater than the slope of object A. Thus the speed of B is greater than that of A.

Question 8.
Find the distance covered by a particle during the time interval which the speed-time graph is-shown in figure.
Answer:

Distance covered in the. time interval 0 to 20s is equal to the area of the triangle OAB.
Area of A OAB. \(\frac { 1 }{ 2 }\) × base × height
\(\frac { 1 }{ 2 }\) × 20 x 20 = 200 ms^-1

Question 9.
A car moves 30 km in 30 min and the next 30 km in 40 min. Calculate the average speed for the entire journey.
Answer:
Answer:
Total time taken = 30 + 40 = 70 min. = \(\frac { 70 }{ 60 }\) hour
Total distance = 30 + 30 = 60 km

Question 10.
A boy travels a distance of 3m due east and then 4m due north.
(a) How much is the total distance covered?
(b) What is the magnitude of the displacement?
Answer:

(a) Total distance covered = 3 + 4 = 7m
(b) Net displacement: OB² = OA² + AB²
= 3² + 4²
OB² = 25m²
∴OB = 5m 0 3m
Net displacement = 5m

Question 11.
During an experiment, a signal from a spaceship reached the ground station in five seconds. What was the distance of the spaceship from the ground station? The signal
travels at the speed of light that is 3 × 10⁸ ms^-1
Answer:
Time taken = 5 seconds.
Speed of signal u = 3 × 10⁸ m/s ?
Distance = ?
Speed = Distance / Time
∴ Distance = Speed × Time
Distance = 3 × 10⁸ × 5 = 15 × 10⁸ m.

Question 12.
A train travelling at a speed of 90kmph. Brakes are applied so as to produce a uniform acceleration of -0.5 ms-2. Find how far the train will go before it is brought to rest?
Answer:
Here we have
Initial velocity , u = 90km/h
\(=\frac{90 \times 1000 \mathrm{~m}}{60 \times 60 \mathrm{~s}}=25 \mathrm{~m} / \mathrm{s}\)
Final velocity, v = 0
Acceleration, a = -0.5m/s²
Thus, distance travelled = ?
We know that, v² = u² + 2as

Question 13.
The adjacent diagram shows the velocity-time graph of the body.
a) During what time interval is the motion of the body accelerated?
Answer:
At 0 to 4 second

b) Find the acceleration in the time Interval mentioned in part ‘a’.
Answer:
\(\mathrm{a}=\frac{v-u}{t}=\frac{30-0}{4}=7.5 \mathrm{~m} / \mathrm{s}^{2}\)

c) What is the distance travelled by the body in the time interval mentioned ¡n part ‘a’?
Answer:Distance travelled Area under the graph
= Area of the triangle = 1/2 bh
= 1/2 × 4 × 30 = 60m

Question 14.
The following graph shows the motion of a car. What do you infer from the graph along with OA and AB? What is the speed of the car along with AB and what time it reached this speed?
a) What do you infer from the graph along OÄ and AB
Answer:
Graph along with OA: The car travels with uniform acceleration and uniform motion.
Graph along with AB : The car travels with constant speed and unaccelerated motion.

b) What is the speed of the car along AB?
Answer:
Along AB : The speed of the car is constant.
From the graph, it seems the speed along AB is 72 km/hr.

c) What time it reached this speed
Answer:
It reaches this speed after 3.2 hours, that is, 3 hours, 12 minutes.

Question 15.
From the following table, check the shape of the graph.

Answer:

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 1 Measurement Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 1 Measurement

9th Science Guide Measurement Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Choose the correct one.
(a) mm < cm < m < km
(b) mm > cm > m > km
(c) km < m < cm < mm
d) mm > m > cm > km
Answer :
(a) mm < cm < m < km

Question 2.
Rulers, measuring tapes and metre scales are used to measure
(a) mass
(b) weight
(c) time
(d) length
Answer:
(d) length

Question 3.
1 metric ton is equal to
(a) 100 quintals
(b) 10 quintals
(c) 1/10 quintals
(d) 1/100 quintals
Answer :
(b) 10 quintals

Question 4.
Which among the following is not a device to measure mass?
(a) Spring balance
(b) Beam balance
(c) Physical balance
(d) Digital balance
Answer :
(a) Spring balance

II. Fill in the blanks :

1. Metre is the unit of …………..
Answer :
length

2. 1 kg of rice is weighed by ……………
Answer :
beam balance

3. Thickness of a cricket ball is measured by ……………..
Answer :
vernier caliper

4. Radius of a thin wire is measured by …………………
Answer :
screw gauge

5. A physical balance measures small differences in mass up to ……………….
Answer :
1mg or less

III. State whether true or false. If false, correct the statement :

1. The SI unit of electric current is kilogram.
Answer:
False.
Correct statement: The SI unit of electric current is ampere.

2. Kilometre is one of the SI units of measurement.
Answer:
True.

3. In everyday life, we use the term weight instead of mass.
Answer:
True.

4. A physical balance is more sensitive than a beam balance.
Answer:
True.

5. One Celsius degree is an interval of IK and zero degree Celsius is 273.15 K.
Answer:
True.

6 . With the help of vernier caliper we can have an accuracy of 0.1 mm and with screw gauge we can have an accuracy of 0.01 mm.
Answer:
True.

IV. Match the following:

Question 1.

Column I	Column II
Length	kelvin
Mass	metre
Time	kilogram
Temperature	second

Answer:

Column I	Column II
Length	metre
Mass	kilogram
Time	second
Temperature	kelvin

Question 2.

Column I	Column II
Screw gauge	Vegetables
Vernier caliper	Coins
Beam balance	Gold ornaments
Digital balance	Cricket ball

Answer:

Column I	Column II
Screw gauge	Coins
Vernier caliper	Cricket ball
Beam balance	Vegetables
Digital balance	Gold ornaments

V. Assertion and reason type :

Mark the correct answer as :
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true

Question 1.
Assertion (A) : The scientifically correct expression is “The mass of the bag is 10 kg”
Reason (R) : In everyday life, we use the term weight instead of mass.
Answer :
(a) Both A and R are true but R is not the correct reason

Question 2.
Assertion (A) : 0° C = 273.16 K. For our convenience we take it as 273K after rounding off the decimal.
Reason (R) : To convert a temperature on the Celsius scale we have to add 273 to the given temperature.
Answer :
(b) Both A and R are true and R is the correct reason

Question 3.
Assertion (A) : Distance between two celestial bodies is measured in terms of light year.
Reason (R) : The distance travelled by the light in one year is one light year.
Answer:
(d) A is false but R is true
Distance between two celestial bodies is measured in terms of unit.

VI. Answer very briefly.

Question 1.
Define measurement.
Answer :
Measurement is the process of comparison of the given physical quantity with the known standard quantity of the same nature.

Question 2.
Define a standard unit.
Answer:
Unit is the quantity of a constant magnitude which is used to measure the magnitudes of other quantities of the same nature.

Question 3.
What is the full form of SI system?
Answer:
The full form of S.I. system is the International System of Units.

Question 4.
Define least count of any device.
Answer:
Least count is the least measurement possible in a given device.
It is the distance moved by the tip of the screw for a rotation of one division on the head scale.
Least count = [Pitch / No. of head scale divisions]

Question 5.
What do you know about pitch of screw gauge?
Answer:
Pitch of the screw gauge is the distance between two successive screw threads. It is measured by the ratio of distance travelled on the pitch scale to the number of rotations of the head scale.

Question 6.
Can you find the diameter of a thin wire of length 2 m using the ruler from your instrument box?
Answer:
No, I can not find the diameter of a thin wire of length 2 m using the ruler.

VII. Answer briefly :

Question 1.
Write the rules that are followed in writing the symbols of units in SI system.
Answer:

•  The units named after scientists are not written with a capital initial letter.
  E.g. newton, henry, ampere, and watt.
• The symbols of the units named after scientists should be written by the initial capital letter.
  E.g. N for newton, H for Henry, A for ampere, and W for watt.
• Small letters are used as symbols for units not derived from a proper noun.
  E.g. m for metre, kg for kilogram.
•  No lull stop or other punctuation marks should be used within or at the end of symbols.
  E.g. 50 m and not as 50 m.
•  The symbols of the units are not expressed in plural form.
  E.g. 10 kg not as kgs.

Question 2.
Write the need of a standard unit.
Answer:
A Standard Unit is needed to maintain uniformity in measurements like length, weight, size and distance. Eg: Standard Unit of length is metre.

Question 3.
Differentiate mass and weight.
Answer:
Mass:

1.  Fundamental quantity
2.  Has magnitude alone – scalar quantity
3.  It is the amount of matter contained in a body
4.  Remains the same
5.  It is measured using physical balance
6.  Its unit is kilogram

Weight:

1.  Derived quantity
2.  Has magnitude and direction – vector quantity
3.  It is the normal force exerted by the surface on the object against gravitational pull
4.  Varies from place to place
5.  It is measured using spring balance
6.  Its unit is newton

Question 4.
How will you measure the least count of vernier caliper?
Answer:
The least count of Vernier Caliper is the ratio of the value of one smallest main scale division to total
a number of Vernier scale divisions.
i.e., L.C. = 0.1mm = 0.01cm
(or) L.C. = 1MD – 1VSD = 1.0 mm – 0.9 mm = 0. 1mm = 0.01 cm

VIII. Answer in detail :

Question 1.
Explain a method to find the thickness of a hollow teacup.
Answer:
Step 1 : The Pitch, Least count and the type of zero error of the screw gauge are determined.
Step 2 : The given cup is placed in between two studs.
Step 3 : The head screw using the ratchet arrangement is freely rotated until the given cup is held firmly, but not tightly.
Step 4 : Pitch scale reading (PSR) by the head scale and head scale coincidence (HSC) with the axis of the pitch scale, are found.
Step 5 : The readings are recorded and the experiment for different positions of the given cup is repeated.
Step 6 : The thickness of the cup is calculated using the formula P.S.R + (HSC × L.C)
Step 7 : Then the average of the last column of the table, is found. Hence the thickness of a hollow tea cup = ………….. mm.

Question 2.
How will you find the thickness of a one rupee coin?
Answer:
Step 1 : The Pitch, Least count and the type of zero error of the screw gauge are determined.
Step 2 : The given coin is placed in between two studs.
Step 3 : The head screw using the ratchat arrangement is freely rotated until given one rupee coin is held firmly, but not tightly.
Step 4 : Pitch scale reading (PSR) by the head scale and head scale coincidence (HSC) with are axis of the pitch scale are found.
Step 5 : The reading are recorded and the experiment for different positions of the given coin is repeated.
Step 6 : The thickness of the coin is computed using the formula P.S.R + (HSC x L.C )
Step 7 : Then the average of the last column of the table is found.

mean = …………….. mm
Hence the thickness of a one rupee coin = ……………….. mm

IX. Numerical Problems :

Question 1.
Inian and Ezhilan argue about the light year. Inian tells that it is 9.46 x 10¹⁵m and Ezhilan argues that it is 9.46 x 1012 km. Who is right? Justify your answer.
Answer:
(Inian is correct)
Light travels 3 × 10⁸m in one second or 3 Lakhs kilometre in one second.
In one year we have 365 days.
The total number of second in one year is equal to 365 x 24 x 60 x 60
Distance travelled by light in 1 year = (3.153 x 10⁷) x (3 x 10⁸)
= 9.46 x 10¹⁵m

Question 2.
The main scale reading while measuring the thickness of a rubber ball using Vernier caliper is 7 cm and the Vernier scale coincidence is 6. Find the radius of the ball.
Answer:
MSR = 7 cm
VC = 6cm
LC = 0.1mm = 0.1cm
Diameter = DR = MSR + (VC X LC)
= 7 + 0.06 cm
Diameter D = 7.06 cm
Radius R = \(\frac{D}{2}=\frac{7.06}{2}\) = 0.035 m
The radius of the ball = 0.0353 m.

Question 3.
Find the thickness of a five rupee coin with the screw gauge, if the pitch scale reading is 1 mm and its head scale coincidence is 68.
Answer:
PSR = 1 mm = 1 x 10^-3m
HSC = 68
LC = 0.01 mm =0.01 × 10^-3m
Total reading = PSR + (HSC × LC)
∴Thickness of the five rupee coin = 1 × 10^-3 + (68 × 0.01 × 10^-3 )m
∴ Thickness of the five rupee coin = 1.68 × 10^-3m = 1.68mm

Question 4.
Find the mass of an object weighing 98 N.
Answer:
W = mg
W =98 N
g = 9.8 m/s²
m = \(\frac{\mathrm{W}}{\mathrm{g}}=\frac{98}{9.8}\) = 10 kg

Intext Activities

ACTIVITY – 1

Using Vernier caliper find the outer diameter of your pen cap.

Aim : To find the outer diameter of the pen cap.
Materials required : Vernier caliper, pen cap.
Answer:

Result: The outer diameter of the pen cap = 9.35 cm
[End of the activity]

ACTIVITY – 2

Determine the thickness of a single sheet of your science textbook with the help of a Screw gauge.

LC = Least Count
PSR = Pitch Scale Reading
HSC = Head Scale Coincidence
HSR = Head Scale Reading
TR = Total Reading
Result : The thickness of the single sheet = 0.30
End of the activity

9th Science Guide Measurement Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Length is ……………….
(a) The amount of matter in an object
(b) The amount of space an object takes up.
(c) The distance between two points.
(d) The amount of stuff in an object
Answer:
(c) The distance between two points

Question 2.
Mass is ………………….
(a) The distance between two points
(b) The distance between three points
(c) The amount of matter contained in an object
(d) The amount of space an object occupies.
Answer:
(c)The amount of matter contained in an object

Question 3.
Unit used to measure length
(a) metre
(b) litre
(c) gram
(d) cubic metre (m³)
Answer:
(a) metre

Question 4.
Unit which is used to measure mass
(a) ml
(b) 1
(c) cm
(d) gram
Answer:
(d) gram

Question 5.
How many metres are there in 1 nanometer?
(a) 10^-10m
(b) 10^-9m
(c) 10⁹m
(d) 10¹⁰m
Answer:
(b) 10^-9m

Question 6.
What unit will you use to measure the length of our classroom?
(a) km
(b) m
(c) cm
(d) mm
Answer :
(b) m

Question 7.
The Kelvin is the basic unit of ………………..
(a) temperature
(b) mass
(c) length
(d) volume
Answer :
(a) temperature

Question 8.
……………….consists of ‘U’ shape metal frame
(a) Screw gauge
(b) Vernier caliper
(c) Beam balance
(d) Spring balance
Answer :
(a) screw gauge

Question 9.
Least count of a vernier caliper is ……………. cm.
(a) 1
(b) 0.1
C) 0.01
(d) 0.001
Answer:
(c) 0.01

Question 10.
If no object is placed on the hook, then the pointer of the spring balance reads ………………….
(a) 3
(b) 2
(c) 1
(d) 0
Answer :
(d) 0

Question 11.
SI unit of mass and weights are ………………….
(a) kg, N
(b) N, kg
(c) K, N
(d) N, K
Answer:
(a) kg, N

Question 12.
Units named after scientists …………………..
(a) lowercase
(b) upper case
(c) both (a) and (b)
(d) neither (a) or (b)
Answer:
(a) lower case

Question 13.
An instrument that is used to measure the diameter of a cricket ball is ………………….
(a) Screw gauge
(b) Meter scale
(c) Vernier caliper .
(d) Spring balance
Answer:
(a) Vernier caliper

Question 14.
Distance between Chennai and Kanyakumari can be found in
(a) Kilometres
(b) Metres
(c) Centimetres
(d) Millimetres.
Answer:
(a) Kilometres

II. Fill in the blanks :

1. The precision of vernier calipers is ……………. mm.
Answer:
(a) 0.1mm

2. The gravity accelerates an object, the distance fallen is proportional to …………………
Answer:
time squared

3. SI unit of electric current is ………………
Answer:
ampere

4. Larger unit for measuring time is ………………..
Answer:
millennium

5. The value of an astronomical unit is ……………………
Answer:
1.496 x 10¹¹

6. Mass is a …………….. quantity.
Answer:
scalar

III. State whether true or false. If false, correct the statement:

1. The precision of screw gauge is 0.001 cm.
Answer:
True.

2. The unit of amount of substance is candela
Answer:
False.
Correct statement: The unit of amount of substance is mole.

3. The symbol for the units derived from the names of scientists are written in capital letter
Answer:
True.

4. Yard was used as the unit of length.
Answer:
True

5. Micron is also known as micro-metre
Answer:
True

6. A vemier caliper using the scale invented by Galileo.
Answer:
False.
Correct statement: A vernier caliper using the scale invented by Pierre Vernier.

7. The SI unit of mass is kg.
Answer:
True.

8. Weight has both magnitude and direction.
Answer:
True.

IV. Match the following:

Question 1.

Column I	Column II
FPS	Metre, kilogram and second
CGS	Foot, pound and second
MKS or SI	centimetre, gram and second

Answer:

Column I	Column II
FPS	Foot, pound and second
CGS	centimetre, gram and second
MKS or SI	Metre, kilogram and second

Question 2.

Column-I	Column-II
10 years	1 year
10 centuries	1century(100 years)
10 decades	1 millennium
365.24 days	1 decade

Answer:

Column-I	Column-II
10 years	1 decade
10 centuries	1 millennium
10 decade	1century(100 years)
365.24 days	1 year

Question 3.

Column-I	Column-II
Electric Current	radian
Luminous intensity	ampere
Angle	steradian
Solid angle	candela

Answer:

Column-I	Column-II
Electric Current	ampere
Luminous intensity	candela
Angle	radian
Solid angle	steradian

Question 4.

Column-I	Column-II
Length	s
Mass	m
Time	k
Temperature	kg

Answer:

Column-I	Column-II
Length	m
Mass	kg
Time	s
Temperature	k

Question 5.

Column-I	Column-II
Millimeter	10-15 m
Nanometer	10-3m
Angstrom	10-9m
Fermi	10-10m

Answer:

Column-I	Column-II
Millimeter	10-3m
Nanometer	10-9m
Angstrom	10-10m
Fermi	10-15 m

Question 6.

Column-I	Column-II
Temperature	Bearm balance
Mass	Ruler
Length	Digital clock
Time	Thermometer

Answer:

Column-I	Column-II
Temperature	Thermometer
Mass	Bearm balance
Length	Ruler
Time	Digital clock

V. Assertion and reason type :

Question 1.
Assertion (A) : Light year and wave length both measure distance
Reason (R) : Both have dimensions of time.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and R is the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer :
(c) A is true but R is false

Question 2.
Assertion (A) : Density is a derived physical quantity
Reason (R) : Density cannot be derived from the fundamental physical quantities.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and,R-is the correct explanation of A.
(c) A is true but R is false. .
(d) A is false but R is true.
Answer :
(c) A is true but R is false
Correct statement: Density can be derived from mass and volume.

Question 3.
Assertion (A) : Mass, Length and Time are fundamental physical quantities.
Reason (R) : They are independent of each other.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and R is the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer :
b) Both A and R are true and R is the correct explanation of A

Question 4.
Assertion (A) : The SI system of units is the improved system of units for measurement.
Reason (R) : The SI unit of mass is kilogram.
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true.
Answer :
(b) Both A and R are true and R is the correct reason

Question 5.
Assertion (A) : The skill of estimation is important for all of us in our daily life.
Reason (R) : The skill of estimation reduces our consumption of time.
a) Both A and R are true but R is not the correct reason.
b) Both A and R are true and R is the correct reason.
c) A is true but R is false. ,
d) A is false but R is true.
Answer :
(b) Both A and R are true and R is the correct reason

VI. Comprehensive type :

(a) The speed of a body gives us an idea of how slow or fast that a body is moving. Speed of a body is the distance travelled by it per unit time. The SI unit of speed is metre per second. It is a scalar quantity. The speed of a running cab at any instant of time is shown by an instrument called, ’speedometer’ and the distance travelled by a car is measured by another instrument called, ‘odometer’.

Question 1.
Which the following is not a correct unit of speed?
(a) cm/s
(b) m/s
(e) km/h
(d) km/s.
Answer :
(d) km/s

Question 2.
If the distance travelled by the cab in 3 hours is 120 km, then its speed will be
(a) 40 m/s
(b) 40 km/s
(c) 40 km/h
(d) 40 km/min
Answer :
(c) 40 km/h

Question 3.
The formula for finding the speed of the cab is
(a) Distance = speed x time
(b) velocity = distance x time
(c) time = distance x velocity
(d) None of these.
Answer:
(a) Distance = speed x time

(b) Read the passage and answer the questions given below.

Mass is the amount of matter contained in an object. Measurement of mass helps us to distinguish between lighter and a heavier body. Beam-Balance, spring balance and electronic balance are used to measure mass of different objects. The SI unit of mass is kilogram (kg). But different units are Used to measure the mass of different objects depending upon their weight, e.g. weight (mass) of a tablet is measured in milligrams (mg), weight of a student is measured in kilogram (kg), and weight of a truck with goods is measured in metric tons. 1 metric ton is equal to 10 quintals and 1 quintal is equal to 100 kg. 1 gram is equal to 1000 mg.

Question 1.
The value of 1 metric ton is equal to
(a) 1000 kg
(b) 10 quintals
(c) 1000,000 g
(d) 100 kg
Answer :
(a) 1000 kg (or) (b) 10 quintals

Question 2.
How will you measure weight of a tablet?
(a) kg
(b) g
(c) mg
(d) none of these.
Answer:
(c) mg

VII. Answer very briefly :

Question 1.
Write the units which are used to measure long distances.
Answer:
km, AU, light-year, parsec.

Question 2.
Define Astronomical unit.
Answer:
AU is defined as the average distance between the earth and the sun.
1 AU = 1.496 × 10¹¹m.

Question 3.
Define the light year.
Answer:
The distance travelled by light in one year in vacuum. 1 light-year = 9.46 × 10¹⁵m.

Question 4.
Convert the temperature from Fahrenheit into Celsius & Kelvin.
Answer:

Question 5.
Convert 100°C into Kelvin.
Answer:
100 + 273 = 373 K. ie. °C + 273

Question 6.
Convert 112°F into K.
Answer:

Question 7.
Write the principle of screw gauge.
Answer:

• When a screw is rotated in a nut, the distance moved by the tip of the screw is directly proportional to the number of rotations given.
• Hence the principle of the screw is considered as the principle of screw gauge.

Question 8.
What are the kinds of units?
Answer:

1. Fundamental or basic units
2. Derived units

Question 9.
Give some examples of fundamental units.
Answer:
The examples of fundamental units are kg for mass,m for length, s for time.

Question 10.
Give some examples of derived units.
Answer:
The units of area, volume, density.

Question 11.
What is the standard unit of weight?
Answer:
Newton is the standard unit of weight.

Question 12.
What is the standard unit of mass?
Answer:
kilogram is the standard unit of mass.

Question 13.
Define Mass.
Answer:
Mass is the amount of matter contained in a body.

Question 14.
Define Weight.
Answer:
The force with which the earth attracts a body towards its center is called weight.

Question 15.
What is the SI unit of temperature?
Answer:
Kelvin is the SI unit of temperature.

Question 16.
What is the measuring unit of the thickness of a plastic carry bag?
Answer:
1 micron = 10^-6m (or) μm.

VIII. Answer briefly :

Question 1.
Write temperature conversion.
Answer:
Temperature Conversion (Exact)

Question 2.
Write about the positive zero error in screw gauge instrument.
Answer:
When the plane surface of the screw and the opposite plane stud on the frame are brought into contact, if the zero of the head scale lies below the pitch scale axis, the zero error is positive. For example, the 5th division of the head scale coincides with the pitch scale axis, then the zero error is positive and is given by Z.E = + (n × LC) where ‘n’ is the head scale coincidence. In this case, Zero error = + (5 × 0.01) = 0.05 mm. So the zero correction is – 0.05 mm

Question 3.
Write SI units for the fundamental quantity.
Answer:

Basic Quantity	Unit
Length	metre
Mass	kilogram
Time	second
Electric current	ampere
Temperature	kelvìn
Amount of substance	mole
Luminous intensity	candela

Question 4.
Convert the following units in metre.
Answer:

Smaller units	Value in metre
Centimeter (cm)	10-2 m
Millimeter (mm)	10-3 m
micron or µm	10-6 m
nanometre (nm)	10-9 m
angstrom (A)	10-10 m
fermi (f)	10-15 m

Question 5.
Draw and mark the parts of vernier caliper
Answer:
PARTS Marked in the Vernier caliper

1. Lower fixed jaw
2. Upper fixed jaw
3. Lower movable jaw
4. Vernier scale
5. Retainer
6. Main scale
7. Depth probe.

IX. Numerical Problems :

Question 1.
A piece of iron of volume 40cm³ whose density is 6.8g/cm³. Find the mass of iron.
Answer:
Given, density of iron, D = 6.8g/cm³
volume of iron, V = 40 cm³
mass of iron, M = V × D [∴ mass = volume × density]

m = 272.0g.

Question 2.
Solve : The mass of 40 apples in a box is 5 kg.
(i) Find the mass of a dozen of them.
(ii) Express the mass of one apple in gram.
Answer:
(i)  40 apple = 5 kg 5000 g
1 apple =\(\frac{500 \not 0}{4 \not \emptyset}\)
1 apple 125 g
∴ 1 dozen 12 apples
12 apples 125 × 12 g
12 apples 1500 g.

(ii)  40 apples = 5000 g

1 apple = \(\frac{5000}{40} \mathrm{~g}\)

1 apple = 125 g
The mass of 1 apple = 125 g

X. Answer in detail :

Question 1.
How will you find Zero Error of the screw gauge?
Answer:
Zero Error of a screw gauge :
When the plane surface of the screw and the opposite plane stud on the frame area brought into contact, if the zero of the head scale coincides with the pitch scale axis there is no zero error.

Positive zero error:
When the plane surface of the screw and the opposite plane stud on the frame are brought into contact, if the zero of the head scale lies below the pitch scale axis, the zero error is positive. For example, the 5th division of the head scale coincides with the pitch scale axis, then the zero error is positive and is given by
Z.E = + (n x LC) where ‘n’ is the head scale coincidence. In this case, Zero error = + (5 x 0.01) = 0.05mm. So the zero correction is -0.05 mm.

Negative zero error:
When the plane surface of the screw and the opposite plane stud on the frame are brought into contact, if the zero of the head scale lies above the pitch scale axis, the zero error is negative. For example, the 95th division coincides with the pitch scale axis, then the zero error is negative and is given by
ZE = -(100-n) × LC
ZE = – (100 – 95) × LC
= -(5 × 0.01)
= – 0.05 mm
The zero correction is + 0.05mm

Question 2.
How will you find Zero Error of Vernier Caliper? Explain.
Answer:
Zero error:

• Unscrew the slider and move it to the left, such that both the jaws touch each other. Check whether the zero marking of the main scale coincides with that of the Vernier scale.
• If they are not coinciding with each other, the instrument is said to posses zero error. Zero error may be positive or negative.
• If the zero mark of the Vernier is shifted to the right, it is called positive error.
• On the other hand, if the Vernier zero is shifted to the left of the main scale zero marking, then the error is negative.

Positive zero error:

• From the figure you can see that zero of the vernier scale is shifted to the right of zero of the main scale.
• In this case the reading will be more than the actual reading.
• Hence, this error should be corrected. In order to correct this error, find out which vernier division is coinciding with any of the main scale divisions.
• Here, fifth vernier division is coinciding with a main scale division.
• So, positive zero error = +5 × LC = +5 × 0.01 = 0.05 cm.
  

Negative zero error:

• You can see that zero of the vernier scale is shifted to the left of the zero of the main scale.
• So, the obtained reading will be less than the actual reading.
• To correct this error we should first find which vernier division is coinciding with any of the main scale divisions, as we found in the previous case.
• In this case, you can see that sixth line is coinciding. But, to find the negative error, we can count backward (from 10).
• So, the 4th line is coinciding. Therefore, negative zero error = -4 x LC = -4 x 0.01 = -0.04 cm.
  

Question 3.
Write short note on the following :
(i) Common balance
(ii) Physical balance Digital balance Spring balance
Answer:
Common (beam) balance :
A beam balance compares the sample mass with a standard reference mass (Standard reference masses are 5g, 10g, 20g, 50g, 100g, 200g, 500g, 1kg, 2kg, 5kg). This balance can measure mass accurately up to 5 g

Physical balance:
This balance is used in labs and is similar to the beam balance but it is a lot more sensitive and can measure mass of an object correct to a milligram.
The standard, reference masses used in this physical balance are 10 mg, 20 mg, 50 mg, 100 mg, 200 mg, 500 mg, 1 g, 2g, 5 g, 10 g, 20 g, 50 g, 100g, and 200 g.

Digital balance:
Nowadays, for accurate measurements digital balances are used, which measure mass accurately even up to a few milligrams, the least value being 10 mg (Figure 1.11). This electrical device is easy to handle and commonly used in jewellery shops and labs.

Spring balance:
This balance helps us to find the weight of an object. It consists of a spring fixed at one end and a hook attached to a rod at the other end. It works by ‘Hooke’s law’ which states that the addition of weight produces a proportional increase in the length of the spring. A pointer is attached to the rod which slides over a graduated scale on the right. The spring extends according to the weight attached to the hook and the pointer reads the weight of the object on the scale.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 4 Electric Charge and Electric Current Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 4 Electric Charge and Electric Current

9th Science Guide Electric Charge and Electric Current Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
In current electricity, a positive charge refers to,
(a) presence of electron
(b) presence of proton
(c) absence of electron
(d) absence of proton
Answer:
(c) absence of electron

Question 2.
Rubbing of comb with hair
(a) creates electric charge
(b) transfers electric charge
(c) either (a) or (b)
(d) neither (a) nor (b)
Answer:
(b) transfers electric charge

Question 3.
Electric field lines ……………….. from positive charge and ……………………..in negative charge.
(a) start; start
(b) start; end
(c) start: end
(d) end; end
Answer:
(b) or (c) start, end

Question 4.
Potential near a charge is the measure of its……………to bring a positive charge at that point.
(a) force
(b) ability
(c) tendency
(d) work
Answer:
(d) work

Question 5.
Heating effect of current is called,
(a) Joule heating
(b) Coulomb heating
(c) Voltage heating
(d) Ampere heating
Answer:
(a) Joule heating

Question 6.
In an electrolyte, the current is due to the flow of
(a) electrons
(b) positive ions
(c) both (a) and (b)
(d) neither (a) nor (b)
Answer:
(c) both (a) and (b)

Question 7.
Electroplating is an example of
(a) heating effects
(b) chemical effects
(c) flowing effects
(d) magnetic effect
Answer:
(b) chemical effect

Question 8.
Resistance of a wire depends on,
(a) temperature
(e) nature of material
(b) geometry
(d) all the above
Answer:
(d) all the above

II. Match the following

1. Electric Charge	(a) ohm
2. Potential difference	(b) ampere
3. Electric field	(c) coulomb
4. Resistance	(d) newton per coulomb
5. Electric current	(e) volt

Answer:
1 – c, 2 – e, 3 – d, 4 – a, 5 – b

III. State whether true or false. If false, correct the statement:

1. Electrically neutral means it is either zero or equal positive and negative charges.
Answer:
True.

2. Ammeter is connected in parallel in an electric circuit.
Answer:
False.
Correct statement: Ammeter is connected in series in an electric circuit.

3. The anode in the electrolyte is negative.
Answer:
False.
Correct statement: The anode in the electrolyte is positive.

4. Current can produce the magnetic field.
Answer:
True.

IV. Fill in the blanks :

1. Electrons move from …………….. potential to …………….. potential.
Answer:
lower, higher

2. The direction opposite to the movement of electron is called …………….. current.
Answer:
conventional

3. The e.m.f of a cell is analogues to a pipeline.
Answer:
water pump

4. The domestic electricity in India is an ac with a frequency of Hz.
Answer:
50

V. Conceptual Questions:

Question 1.
A bird sitting on a high power electric line is still safe. How?
Answer:
Birds don’t get shocked when they sit on electrical wires because they are not good conductors of electricity. Electricity flowing through a single power line at 35,000 volts will continue along the path of least resistance and bypass birds because there is no difference in electrical potential.

Question 2.
Does a solar cell always maintain the potential across its terminals constant? Discuss.
Answer:
Solar cell delivers a constant current for any given illumination level, while the voltage is determined by the load resistance. Potential in a solar cell depends on the intensity of solar radiation. Since the intensity of solar radiation is not always constant, the potential across its terminal is also not constant.

Question 3.
Can electroplating be possible with the alternating current?
Answer:
Electroplating is a process where there is a continuous flow of ions for the deposition of copper, which is not possible in an Alternating current. Therefore, electroplating is possible with DC only, for the sake of perfectness and homogeneity of the electroplating.

VI. Answer the following:

Question 1.
On what factors does the electrostatic force between two charges depend?
Answer:
The electrostatic force between two charges depend on the following factors;

• value of charges on them,
  
• distance between them, and
  
• nature of medium between them.

Question 2.
What are the electric lines of force?
Answer:
The lines representing the electric field are called electric lines of force.

Question 3.
Define electric field.
Answer:
The electric lines of force are straight or curved paths along which a unit positive charge tends to move in the electric field.

Question 4.
Define electric current and give its unit.
Answer:
The electric current is defined as the rate of flow of electric charge through any section of a conductor.
Electric current I = Q/t
Its unit is Cs^-1
Its SI unit: ampere (A).

Question 5.
State Ohm’s law.
Answer:
Ohm’s law states that electric potential difference across two points in an electrical circuit is directly proportional to the current passing through it. That is V ~ I
The proportionality constant is the resistance (R) offered between the two points.
Hence, Ohm’s law is written as V = RI (or) V = IR
Where, V is the potential difference in volt (V), I is the current flow in ampere (A), R is the resistance in ohm (Ω)

Question 6.
Name any two appliances which work under the principle of heating effect of current.
Answer:
Electric heating appliances like an iron box, water heater, toaster, etc.

Question 7.
How are the home appliances connected in general, in series or parallel? Give reasons.
Answer:
The home appliances are connected in parallel. This is because, when the appliances are connected in parallel, each of them can be switched on and off independently. This is a feature that is essential in house wiring. Also, if the appliances were wired in series, the potential difference across each appliance would vary depending on the resistance of the appliance.

Question 8.
List the safety features whilehandling electricity.
Answer:
(i) Ground connection: The metal bodies of all the electrical appliances are to be connected to the ground by means of a third wire apart from the two wires used for electrical connection.

(ii) Trip switch: It is an electromechanical device which does not allow a current beyond a particular value by automatically switching off the connection.

(iii) Fuse: A fuse is another safety mechanism which works on the joule heating principle.

VII. Exercises:

Question 1.
Rubbing a comb on hair makes the comb get – 0.4C.
(a) Find which material has lost electron and which one gained it.
(b) Find how many electrons are transferred in this process.
Answer:
a. Comb gained electrons. Dry hair lost an electron
b. No. of electrons transferred = -0.4 C
1 coulomb = 6.25 × 10¹⁸ electron
– 0.4 C = 0.4 × 6.25 × 10¹⁸ electrons
= -2.5 × 10¹⁸ electrons

Question 2.
Calculate the amount of charge that would flow in 2 hours through an element of an electric bulb drawing a current of 2.5A.
Answer:
Current I = 2.5 A
time t = 2 hours = 2 × 3600 seconds
t = 7200 s
Amount of charge Q = I × t = 2.5 × 7200
Q = 18,000

Question 3.
The values of the current (I) flowing through a resistor for various potential differences V across the resistor are given below. What is the value of resistor?

[Hint: plot V-I graph and take slope]
Answer:

Intext Activities

ACTIVITY – 1

Take a condemned electronic circuit board in a TV remote or old mobile phone. Look at the electrical symbols used in the circuit. Find out the meaning of the symbols known to you.


[End of the activity]

ACTIVITY – 2
Cut an arrow shaped strip from aluminium foil. Ensure that the head is a fine point. Keep the arrow shaped foil on a wooden board. Connect a thin pin to two lengths of wire. Connect the wires to the terminals of electric cell, may be of 9V. Press one pin onto the pointed tip and the other pin at a point about one or two mm away. Can you see that the tip of aluminum foil starts melting?

Aim :
To understand the heating effect of electric current.

Materials Required :
Aluminum strip, wooden board, bell pins, cell of 9 V.

Procedure :
Cut an arrow shaped strip from aluminum foil. Keep the arrow shaped foil on a wooden board. Connect a pin to two lengths of wire. Connect the wires to the terminals of electric cell of 9 V. Press one pin onto the pointed tip and another pin at a point about one or two mm away.

Observation :
The tip’of aluminum foil starts melting.

Conclusion :
It starts melting because the electrons while moving in the wire suffer resistance. Work is done to overcome the resistance which is converted into heat energy. This conversion of electrical energy into heating energy is called the heating effect of electric current.

ACTIVITY – 3

Take a beaker half filled with copper sulphate solution. Take a carbon rod from a used dry cell. Wind a wire on its upper end. Take a thick copper wire, clean it well and flatten it with a hammer. Immerse both the copper wire and carbon rod in the copper sulphate solution. Connect the carbon rod to the negative terminal of an electric cell and copper wire to the positive terminal of the cell. Also ensure that the copper and the carbon rod do not touch each other, but are close enough. Wait and watch. After some time you would find fine copper deposited over the carbon rod. This is called as electroplating. This is due to the chemical effect of the current.

Aim:
Electroplating carbon rod with copper.

Materials Required:
Beaker, copper sulphate solution, carbon rod, thick copper wire and hammer.

Procedure :

• Take a beaker half filled with copper sulphate solution.
• Take a carbon rod and wind a wire on its upper end.
• Take a thick copper wire, clean it well and flatten it with a hammer.
• Immerse both the copper wire and carbon rod in the copper sulphate solution.
• Connect the carbon rod to the negative terminal of the cell and copper wire to the positive terminal of the cell.
• Ensure both the rods do not touch each other, but are close enough.
• Observe for some time.

Observation :
After some time, we would find fine copper deposited over the carbon rod.

Conclusion :
When the current passes through the copper sulphate solution, the copper ions migrate from the copper sulphate solution towards the cathode (-ve terminal). These copper ions get deposited on the carbon rod and form a coating of a fine layer on it.

This process of coating a metal over another metal by electrolysis is called electroplating. This is due to the chemical effect of electric current.

9th Science Guide Electric Charge and Electric Current Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
A current of 2A passing through the conductor produces 80 J of heat in 10 seconds. The resistance of the conductor is ……………..
(a) 0.5Ω
(b) 2Ω
(c) 4Ω
(d) 20Ω
Answer:
(b) 2Ω

Question 2.
The resistance of a straight conductor is independent of …………………..
(a) temperature
(b) material
(c) cross sectional area
(d) shape of cross section
Answer:
(d) shape of cross section

Question 3.
Two resistances R1 and R2 are connected is parallel. Their equivalent resistance is


Answer:

Question 4.
If in the circuit, power dissipation is 150 W, then R is ……………..

(a) 2Ω
(b) 6Ω
(c) 5Ω
(d) 4Ω
Answer:
(b) 6Ω

Question 5.
The force between two parallel wires carrying currents has been used to define…………..
(a) ampere
(b) coulomb
(c) volt
(d) watt
Answer:
(a) ampere

Question 6.
Electric current passes through a metallic conductor due to the movement of ……………
(a) ions
(b) ampere
(c) electrons
(d) protons
Answer:
(c) electrons

Question 7.
What is the maximum resistance one can make with ten 1Ω resistors?
(a) 1Ω
(b) 2Ω
(c) 5Ω
(d) 10Ω
Answer:
(d) 10Ω

Question 8.
Two conductors of resistance 2 R and R are connected in series in a battery circuit. The ratio of heat developed In them is ……………………
(a) 2 : 1
(b) 1 : 2
(c) 1 : 3
(d) 1 : 4
Ans:
(a) 2 : 11

Question 9.
1 volt = …………..


Answer:

Question 10.
The resistance of a conductor is R. If Its length is doubled, then its new resistance will be ……………….
(a) R
(b) 2R
(c) 4R
(d) 8R
Answer:
(C) 4R

Question 11.
The following is not a safety device.
(a) Fuse
(b) Trip switch
(c) Ground connection
(d) Wire
Answer:
(d) wirel

Question 12.
In India the frequency of alternating current is,
(a) 220 Hz
(b) 50 Hz
(c) 5 Hz
(d) 100 Hz
Answer:
(b) 50 Hz

II. Fill in the blanks:

1. The number of electrons constituting 1-coulomb charge is………………….
Answer:
6.25 × 10¹⁸

2. Resistors are connected in series if the resistance of the electric circuit is to be………………….
Answer:
increased

3. Electric fuse is a wire made up of a material having ………………….melting point.
Answer:
low

4. ………………….is the only non-metal that is a good conductor of electricity.
Answer:
Graphite

5. If the area of cross section of the conductor is doubled its resistance gets ………………….
Answer:
halved

6. A negative charge will move from …………………. to …………………. potential.
Answer:
lower, higher

7. ………………….is work done per unit charge.
Answer:
Potential difference

8. An electrochemical cell converts …………………. energy into …………………. energy.
Answer:
chemical, electrical

9. Three resistors are connected in series with a cell. If the current in each resistor is 1.5A, then the current through the cell will be ………………….. Answer:
1.5A

10. Three resistors are connected in parallel with a battery. If the current in each resistor is 2A, then the current through the battery will be …………………..
Answer:
6A

11. As electrons are revolving in the ………………….of an atom they can be easily removed from an atom and also added to it.
Answer:
orbits

12. If an electron is added in excess to an atom then the atom is ………………….charged.
Answer:
negatively

13. The excess of electrons make an object negative and ………………….of electrons make it positive.
Answer:
deficit

14. Electric charge is ………………….in nature.
Answer:
additive

15. Electric lines of force are ………………….lines.
Answer:
imaginary

16. For an isolated positive charge the electric lines of force are radial…………………. and for an isolated negative charge they are radial…………………..
Answer:
outwards, inwards

17. ………………….at a point is a measure of force acting on a unit positive charge placed at that point.
Answer:
Electric field

18. Electric potential is a measure of the ………………….on the unit positive charge to bring it to that point against all electrical forces.
Answer:
work done

19. The movement of positive charge is called as ………………….
Answer:
conventional current

20. The …………………. is the measure of opposition offered by the component to the flow of electric current through it.
Answer:
resistance

21. The process of conduction of electric current through solution is called………………….
Answer:
electrolysis

22. The device used to convert AC to DC is called………………….
Answer:
rectifier

23. Trip switch is a …………………. safety device.
Answer:
electro mechanical

III. True or False:

1. A fuse is used in an electric circuit to stop high current flowing through the circuit.
Answer:
True.

2. Rheostat is also known as fixed resistance.
Answer:
False.
Correct statement: Rheostat is also known as a variable resistance.

3. An ammeter is always placed in parallel with the circuit.
Answer:
False.
Correct statement: An ammeter is always placed in series with the circuit.

4. The resistance of a dry human body is high.
Answer:
True.

5. For current to flow, one needs art open circuit.
Answer:
Correct statement: For current to flow, one needs a closed circuit.

6. A comb rubbed with hair and brought near pieces of paper attracts them, because both comb and paper get similarly charged.
Answer:
False.
Correct statement: A comb rubbed with hair and brought near pieces of paper attracts them, because both comb and paper get oppositely charged.

7. Overloading of electric circuits can lead to short-circuiting.
Answer:
True.

8. Electrons in outer orbits are called free electrons.
Answer:
True.

9. Electric fuse works on the Joule heating principle.
Answer:
True.

IV. Match the following:

I.

Column I	Column II
1. Resistor	a) Galvanometer
2. Connecting wire	b) Voltmeter
3. Current in an electric circuit	c) Copper
4. Potential difference	d) Constantan

Answer:
1-d, 2-c, 3 -a, 4-b

II.

Column I	Column II
1. Electric power	a) Volt
2. Electrical energy	b) Coulomb
3. Electric charge	c) Watt
c) Watt	d) Joule

Answer:
1-c, 2-d, 3-c, 4-a

V. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion (A): Electric current will not flow between two charged bodies when connected if their charges are the same.
Reason (R): Current is the rate of flow of charge.
Answer:
(d) Assertion is false but the reason is true
Reason: Current will not flow when two bodies are at the same potential. When their charges are the same, their potential may be different. Hence current may flow in this case.

Question 2.
Assertion (A) : A bird perches on a high power line and nothing happens to the bird.
Reason (R) : The level of the bird is very high from the ground.
Answer:
(c) Assertion is true but reason is false
Reason: Electric shock is due to the electric current flowing through a living body. When the bird perches on a single high power line, no current passes through its body. Because its body is at an equipotent surface (i.e.) there is no potential difference. While when a man touches the same line, standing bare foot on the ground the electrical circuit is completed through the ground. The hands of man are at high potential and his feet are at low potential. Hence the large amount of current flows through the body of the man and the person, therefore, gets a fatal shock.

VI. Answer in one word:

Question 1.
Name the force which acts between two point charges obey Newton’s third law.
Answer:
Electrostatic force.

Question 2.
What is the SI unit for the current?
Answer:
ampere (A).

Question 3.
Name the device which is used to measure the strength of the electric current in an electric circuit.
Answer:
Ammeter.

Question 4.
What is the rate at which charges flow past a point on a circuit?
Answer:
Current.

Question 5.
Name a device that helps to maintain a potential difference across conductors.
Answer:
Cell or battery.

Question 6.
What does the circuit symbol represent?
Answer:
Wire crossing without touching each other.

Question 7.
How many electrons accumulate to make 1C of electric charge?
Answer:
1C = 6.25 × 10¹⁸ electrons.

Question 8.
What is the charge of one electron?
Answer:
e= 1.6 × 10^-19C.

Question 9.
What is the measure of the work done on the unit positive charge to bring it to that point against all electrical forces?
Answer:
Electric potential

Question 10.
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer:
Parallel

VII. Subjective Problems:

Question 1.
Calculate the charge passing through a lamp in 2 minutes if the current is 3A.
Solution:
Current I = 3A
Time t = 2 minutes = 120seconds
Charge q = ?
q = I × t = 3 × 120
Charge q = 36.C

Question 2.
Calculate the current in a wire if a charge of 1500 coulomb flows through it in 5 minutes.
Solution:
Charge q = 1500 C
Time t = 5 minutes = 300 seconds
Current I =?
I = q/t = \(\frac{1500}{300}\)
Current I = 5A

Question 3.
A charge of 400C flows through a conductor for 13 minutes and 20 seconds. Find the magnitude of the current flowing through the conductor.
Answer:
Q = 400C
t = 13 min and 20s = 13 × 60 + 20
= 780 + 20
= 800s
Current I = \(\frac{Q}{t}=\frac{400}{800}=0.5 \mathrm{A}\)

Question 4.
10²⁰ electrons, each having a charge of 1.6 x 10^-19 C, flows in a circuit V is 0.1s. What is the current in ampere?
Solution :
n = 10²⁰ electrons
e = 1.6 × 10^-19C
t = 0.1s
Charge q = ne
= 10²⁰ × 1.6 × 10^-19
= 16C
Current I = \(\frac{q}{t}=\frac{16}{0.1}=160 \mathrm{~A}\)
∴ Current = 160 A

VIII. Long Answer Questions

Question 1.
a State Ohm’s law.
b. Draw a circuit diagram for the verification of ohm’s law. Also, plot graphically the variation of current with a potential difference.
Answer:
a. Ohm’s law states that the current passing through a conductor is directly proportional
to the potential difference a cross its ends, provided the physical conditions like temperature density etc. remain unchanged V ∝ I or V = IR.
b.

Question 2.
a. Why is series arrangement not used for domestic cricuits?
b. Explain why fuse wire is always connected in series arrangement.
c. Why are copper and aluminium wires useually employed for electricity transmission?
Answer:
a. Series arrangement is not used for domestic circuits because same current will flow through all the appliances. The equivalent resistance will get added and hence the current drawn by the circuit will be less.

b. Fuse wire is always connected in series in a circuit as it has to check the flow of current through the circuit and prevent the extra flow of current through it.

c. Fuse wire is always connected in series in a circuit as it has to check the flow of current through the circuit and prevent the extra flow of current through it.

Question 3.
Explain the dangers of electricity and precautions to be taken while handling electricity.
Answer:

• Damaged insulation – Do not touch the bare wire, use safety gloves, and stand on an insulating stool or rubber slippers while handling electricity.
• Overheating of cables – use quality ISI certified cable wires for domestic wiring
• Overload of power sockets – do not connect too many electrical devices to a single electrical socket.
• Inappropriate use of electrical appliances – always uses the electrical appliances according to the power rating of the device like AC point, TV point, microwave oven point, etc.
• Environment with moisture and dampness – keep the place where there is electricity out of moisture and wetness as it will lead to leakage of electric current.
• Beyond the reach of children – the electrical sockets are to be kept away from the reach of little children who do not know the dangers of electricity.

Question 4.
Write the difference between resistance in series and in parallel.
Answer:

IX.

Question 1.
Distinguish e.m.f and potential difference.
Answer:
As both e.m.f and potential difference are measured in volt, they may appear the same. But they are not. The e.m.f refers to the voltage developed across the terminals of an electrical source when it does not produce current in the circuit. Potential difference refers to the voltage developed between any two points (even across electrical devices) in an electric circuit when there is current in the circuit.

Question 2.
Some common symbols in the electrical circuit.
Answer:

Question 3.
Write a note on direct current.
Answer:

• Current in electrical circuits is due to the motion of positive charge from higher potential to lower potential or electron from lower to higher electrical potential.
• Electrons move from negative terminal of the battery to positive of the battery. Battery is used to maintain a potential difference between the two ends of the wire.
• Battery is one of the sources for dc current. The dc is due to the unidirectional flow of electric charges. Some other sources of dc are solar cells, thermocouples etc. The graph depicting the direct current is shown in Figure.
  
• Many electronic circuits use dc. Some examples of devices which work on dc are cell phones, radio, electric keyboard, electric vehicles etc.

Question 4.
Write a note on alternating current.
Answer:

• If the direction of the current in a resistor or in any other element changes its direction alternately, the current is called an alternating current.
• The alternating current varies sinusoidally with time. This variation is characterised by a term called as frequency.
• Frequency is the number of complete cycle of variation, gone through by the ac in
  one second. s
• In ac, the electrons do not flow in one direction because the potential of the terminals vary between high and low alternately.
• Thus, the electrons move to and fro in the wire carrying alternating current. It is diagrammatically represented in Figure

Question 5.
Explain the advantages of Ac over Dc.
Answer:

• The voltage of ac can be varied easily using a device called transformer. The ac can be carried over long distances using step-up transformers.
• The loss of energy while distributing current in the form of ac is negligible. Direct current cannot be transmitted as such.
• The ac can be easily converted into dc and generating ac is easier than dc
• The ac can produce electromagnetic induction which is useful in several ways.

X. Define the following:

1. Electric force: The force existing between the charges is called an ‘electric force’.
2. Electric potential: Electric potential is a measure of the work done on the unit positive charge to bring it to that point against all electrical forces.
3. Conventional current and electron current: The movement of the positive charge is called as ‘conventional current’. The flow of electrons is termed as ‘electron current’.
4. Current: Current is the rate at which charges flow past a point on a circuit.
5. Electromotive force (e.m.f.): The e.m.f of an electrical energy source is one volt if one joule of work is done by the source to drive one coulomb of charge completely around the circuit.
6. One ohm: One ohm is the resistance of a component when the potential difference of one volt applied across the component drives a current of one ampere through it.
7. Fixed resistor: A fixed resistor has a resistance of a fixed value. Common types of fixed resistors include carbon film resistors and wire-wound resistors.
8. Variable resistor: A variable resistor has a resistance that can be varied. It is used to vary the amount of current flowing in a circuit.
9. Electrolysis and electrolyte: The process of conduction of electric current through solutions is called ‘electrolysis’. The solution through which the electricity passes is called ‘electrolyte’.
10. Synaptic signals: Extremely weak electric current is produced in the human body by the movement of charged particles. These are called synaptic signals. These signals are produced by the electrochemical process. They travel between the brain and the organs through the nervous system.
11. Magnetic effect of current: A wire or a conductor carrying current develops a magnetic field perpendicular to the direction of the flow of current. This is called the magnetic effect of current.
12. Frequency: Frequency is the number of the complete cycle of variations, gone through by the ac in one second.
13. Rectifier: The device used to convert ac to dc is called a rectifier.
14. Resistance: The measure of opposition offered by the component to the flow of electric current through it.
15. Resistors: The components used for providing resistance are called resistors.