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Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Maths Guide Pdf Chapter 3 Trigonometry Ex 3.12 Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Maths Solutions Chapter 3 Trigonometry Ex 3.12

Choose the correct or the most suitable answer:

Question 1.

(1) √2
(2) √3
(3) 2
(4) 4
Answer:
(4) 4

Explaination:

Question 2.
If cos 28° + sin 28°= k³, then cos 17° is equal to
(1) \(\frac{\mathbf{k}^{3}}{\sqrt{2}}\)
(2) \(-\frac{\mathbf{k}^{3}}{\sqrt{2}}\)
(3) \(\pm \frac{\mathbf{k}^{3}}{\sqrt{2}}\)
(4) \(-\frac{\mathbf{k}^{3}}{\sqrt{3}}\)
Answer:
(1) \(\frac{\mathbf{k}^{3}}{\sqrt{2}}\)

Explaination:
cos 28° + sin 28° = k³
cos 28° + sin (90° – 62°) = k³
cos 28° + cos 62° = k³

2 cos 45° . cos 17° = k³
2 × \(\frac{1}{\sqrt{2}}\) cos 17° = k³
√2 cos 17° = k³
cos 17° = \(\frac{\mathrm{k}^{3}}{\sqrt{2}}\)

Question 3.
The maximum value of
4 sin²x + 3 cos²x + sin \(\) + cos \(\) is
(1) 4 + √2
(2) 3 + √2
(3) 9
(4) 4
Answer:
(1) 4 + √2

Explaination:
4 sin²x + 3 cos²x + sin \(\frac{x}{2}\) + cos \(\frac{x}{2}\)
= sin²x + 3 sin²x + 3 cos²x + sin \(\frac{x}{2}\) + cos \(\frac{x}{2}\)
= sin²x + 3(sin²x + cos²x) + sin \(\frac{x}{2}\) + cos \(\frac{x}{2}\)
= 3 + sin²x + sin \(\frac{x}{2}\) + cos \(\frac{x}{2}\) —– (1)
Maximum value of sin x = 1
sin x = 1 when x = \(\frac{\pi}{2}\)
Maximum value of sin²x = 1
Maximum value is obtained when x = \(\frac{\pi}{2}\)
∴ (1) ⇒ 4 sin² x + 3 cos² x + sin \(\frac{x}{2}\) + cos \(\frac{x}{2}\)
= 3 + 1 + sin \(\left(\frac{90^{\circ}}{2}\right)\) + cos \(\left(\frac{90^{\circ}}{2}\right)\)
= 4 + sin 5° + cos 45°
= 4 + \(\frac{1}{\sqrt{2}}\) + \(\frac{1}{\sqrt{2}}\) = 4 + \(\frac{2}{\sqrt{2}}\)
= 4 + √2

Question 4.

(1) \(\frac{1}{8}\)
(2) \(\frac{1}{2}\)
(3) \(\frac{1}{\sqrt{3}}\)
(4) \(\frac{1}{\sqrt{2}}\)
Answer:
(1) \(\frac{1}{8}\)

Explaination:

Question 5.
If π < 2θ < \(\frac{3 \pi}{2}\), \(\sqrt{2+\sqrt{2+2 \cos 4 \theta}}\) equals to
(1) – 2 cos θ
(2) – 2 sin θ
(3) 2 cos θ
(4) 2 sin θ
Answer:
(1) – 2 cos θ

Explaination:



∴ θ lies in the second quadrant, cos θ is negative in the II^nd quadrant.
∴ \(\sqrt{2+\sqrt{2+2 \cos 4 \theta}}\) = – 2 cos θ

Question 6.
If tan 40° = λ, then

(1) \(\frac{1-\lambda^{2}}{\lambda}\)
(2) \(\frac{1+\lambda^{2}}{\lambda}\)
(3) \(\frac{1+\lambda^{2}}{2 \lambda}\)
(4) \(\frac{1-\lambda^{2}}{2 \lambda}\)
Answer:
(4) \(\frac{1-\lambda^{2}}{2 \lambda}\)

Explaination:

Question 7.
cos 1° + cos 2° + cos 3° + ….. + cos 179° =
(1) 0
(2) 1
(3) – 1
(4) 89
Answer:
(1) 0

Explaination:
cos 1° + cos 2° + cos 3° + ……………… + cos 179°
= (cos 1° + cos 179°) + (cos 2° + cos 178°) + (cos 3° + cos 177°) + …………..

= 2 cos 90° cos 89° + 2 cos 90° . cos 88° + …………….
= 2 × 0 × cos 89°+ 2 × 0 × cos 88° + …………..
= 0

Question 8.
Let f_k(x) = \(\frac{1}{k}\)[sin^kx + cos^kx] where x ∈ R and k ≥ 1. Then f₄(x) – f₆(x) =
(1) \(\frac{1}{4}\)
(2) \(\frac{1}{12}\)
(3) \(\frac{1}{6}\)
(4) \(\frac{1}{3}\)
Answer:
(2) \(\frac{1}{12}\)

Explaination:

Question 9.
Which of the following is not true?
(1) sin θ = – \(\frac{3}{4}\)
(2) cos θ = – 1
(3) tan θ = 25
(4) sec θ = \(\frac{1}{4}\)
Answer:
(4) sec θ = \(\frac{1}{4}\)

Explaination:
We know |cos θ| < 1
sec θ = \(\frac{1}{4}\)
⇒ \(\frac{1}{\cos \theta}\) = \(\frac{1}{4}\)
⇒ cos θ = 4
which is not possible.

Question 10.
cos 2θ cos 2Φ + sin²(θ – Φ) – sin²(θ + Φ) is equal to
(1) sin 2 (θ + Φ)
(2) cos 2 (8 + Φ)
(3) sin 2 (θ – Φ)
(4) cos 2(θ – Φ)
Answer:
(2) cos 2 (8 + Φ)

Explaination:
cos 2θ cos 2Φ + sin²(θ – Φ) – sin²(θ + Φ)


= cos 2θ cos 2Φ – sin 2θ sin 2Φ
= cos(2θ + 2Φ)
= cos 2(θ + Φ)

Question 11.

(1) sin A + sin B + sin C
(2) 1
(3) 0
(4) cos A + cos B + cos C
Answer:
(3) 0

Explaination:

Question 12.
If cos pθ + cos qθ = o and if p ≠ q then θ is equal to(n is any integer)
(1)
(2)
(3)
(4)
Answer:
Given cos pθ + cos qθ = o

Question 13.
If tan α and tan β are the roots of x² + ax + b = 0 then \(\frac{\sin (\alpha+\beta)}{\sin \alpha \sin \beta}\) is equal to
(1) \(\frac{\mathbf{b}}{\mathbf{a}}\)
(2) \(\frac{\mathbf{a}}{\mathbf{b}}\)
(3) –\(\frac{\mathbf{a}}{\mathbf{b}}\)
(4) –\(\frac{\mathbf{b}}{\mathbf{a}}\)
Answer:
(3) –\(\frac{\mathbf{a}}{\mathbf{b}}\)

Explaination:
x² + ax + b = 0
Given tan α and tan β are the roots of the above equation. Then

Question 14.
In a triangle ABC, sin² A + sin² B + sin² C = 2 then the triangle is .
(1) equilateral triangle
(2) isosceles triangle
(3) right triangle
(4) scalene triangle
Answer:
(3) right triangle

Explaination:
On simplifying we get
sin² A + sin² B + sin² C = 2 + 2 cos A cos B cos C
= 2 (given)
⇒ cos A cos B cos C = 0
cos A (or) cos B (or) cos C = 0
⇒ A (or) B (or) C = π/2
⇒ ABC (is a right angled triangle).

Question 15.
If f(θ) = |sin θ| + |cos θ|, θ ∈ R then f(θ) is in the interval
(1) [0, 2]
(2) [1, √2]
(3) [1, 2]
(4) [0, 1]
Answer:
(2) [1, √2]

Explaination:

f(θ) = |sin θ| + |cos θ|
To find the point of intersection of the sine curve and cosine curve solving

Question 16.

(1) cos 2x
(2) cos x
(3) cos 3x
(4) 2 cos x
Answer:
(4) 2 cos x

Explaination:
Consider the numerator cos 6x + 6 cos 4x + 15 cos 2x + 10
cos 6x + 6 cos 4x + 15 cos 2x + 10 = cos 6x + cos 4x + 5 cos 4x + 5 cos 2x + 10 cos 2x + 10
= (cos 6x + cos 4x) + 5 (cos 4x + cos 2x) + 10(cos 2x + 1)

= 2 cos 5x cos x + 10 cos 3x . cos x + 20 cos²x
= 2 cos x (cos 5x + 5 cos 3x + 10 cos x)

= 2 cos x

Question 17.
The triangle of the maximum area with a constant perimeter of 12m
(1) is an equilateral triangle with a side of 4m
(2) is an isosceles triangle with sides 2m, 5m, 5m
(3) is a triangle with sides 3m, 4m, 5m
(4) does not exist.
Answer:
(1) is an equilateral triangle with a side of 4m

Explanation:
A triangle will have a max area (with a given perimeter) when it is an equilateral triangle.

Question 18.
A wheel is spinning at 2 radians/second. How many seconds will it take to make 10 complete rotations?
(1) 10 π seconds
(2) 20 π seconds
(3) 5 π seconds
(4) 15 π seconds
Answer:
(1) 10 π seconds

Explanation:
1 rotation makes 2π^c
Distance travelled in 1 second = 2 radians
So time taken to complete 10 rotations = 6 × 2π = 20 π^c
\(=\frac{20 \pi}{2}=10 \pi\) seconds

Question 19.
If sin α + cos α = b, then sin 2α is equal to
(1) b² – 1, if b ≤ √2
(2) b² – 1, if b > √2
(3) b² – 1, if b ≥ √2
(4) b² – 1, if b < √2
Answer:
(1) b² – 1, if b ≤ √2

Explaination:
sin α + cos α = b
(sin α + cos α)² = b²
sinv α + cos² α + 2 sin α cos α = b²
1 + sin 2α = b²
sin 2α = b² – 1
But – 1 ≤ sin 2α ≤ I
– 1 ≤ b² – 1 ≤ 1
b² – 1 ≤ 1 ⇒ b² ≤ 2
⇒ b ≤ √2
∴ sin 2α = b² – 1 if b ≤ √2

Question 20.
In an ∆ABC
(i) sin \(\frac{\mathbf{A}}{2}\) sin \(\frac{\mathbf{B}}{2}\) sin \(\frac{\mathbf{C}}{2}\) > 0
(ii) sin A sin B sin C > 0,then
(1) Both (i) and (ii) are true
(2) only (1) is true
(3) only (ii) Is true
(4) neither (i) nor (ii) is true
Answer:
(1) Both (i) and (ii) are true

Explaination:
When A + B + C = 180°

When A + B + C = 180° each angle will be lesser than 180°
So sin A, sin B, sin C > 0
⇒ sin A sin B sin C > 0
So both (i) and (ii) are true

Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Maths Guide Pdf Chapter 3 Trigonometry Ex 3.11 Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Maths Solutions Chapter 3 Trigonometry Ex 3.11

Question 1.
Find the principal value of
(i) sin^-1 \(\)
(ii) Cos^-1 \(\)
(iii) cosec^-1 (- 1)
(iv) sec^-1 (- √2)
(v) tan^-1 (√3)
Answer:
(i) sin^-1 \(\frac{1}{\sqrt{2}}\)

(ii) Cos^-1 \(\frac{\sqrt{3}}{2}\)

(iii) cosec^-1 (- 1)

(iv) sec^-1 (- √2)

(v) tan^-1 (√3)

Question 2.
A man standing directly opposite to one side of a road of width x meter views a circular shaped traffic green signal of diameter ‘a’ meter on the other side of the road. The bottom of the green signal Is ‘b’ meter height from the horizontal level of viewer’s eye. If ‘a’ denotes the angle subtended by the diameter of the green signal at the viewer’s eye, then prove that

Answer:
Given Width of the Road = x meter
Diameter of the signal AB = a meter
Height of the signal from the eye level = b meter
In ∆ ADC, DC = x, AC = AB + BC = a + b

Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Maths Guide Pdf Chapter 3 Trigonometry Ex 3.10 Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Maths Solutions Chapter 3 Trigonometry Ex 3.10

Question 1.
Determine whether the following measurements produce one triangle, two triangles or no triangle. ∠B = 88°, a = 23 , b = 2. Solve if solution exists.
Answer:
Using sine formula

= 23 × 0.999
= 22.99
which is not possible
∴ Solution of the given triangle does not exsit.

Question 2.
If the sides of a ∆ ABC are a = 4, b = 6 and C = 8, then show that 4 cos B + 3 cos C = 2.
Answer:
In ∆ ABC Given that a = 4, b = 6, c = 8
Using cosine formula

Question 3.
In a ∆ ABC, if a = √3 – 1, b = √3 + 1 and C = 60° find the other side and other two angles.
Answer:

In a ∆ ABC, Given
a = √3 – 1, b = √3 + 1
C = 60°
Using cosine formula a
C² = a² + b² – 2 ab cos C
= (√3 – 1)² + (√3 + 1)² – 2(√3 – 1) × (√3 + 1) cos 6o°
= 3 – 2√3 + 1 + 3 + 2√3 + 1 – 2 (3 – 1) × \(\frac { 1 }{ 2 }\)
c² = 8 – 2 = 6 ⇒ c = √6
Using sine formula

sin (45° – 30°) = sin 45° . cos 30° – cos 45° sin 30°

From equations (1) and (2), we have
sin A = sin 15° ⇒ A = 15°
In ∆ ABC, we have A + B + C = 180°
15° + B + 60° = 180°
B = 180°- 75°
B = 105°
∴ The required sides and angles are
c = √6, A = 15°, B = 105°

Question 4.
In any ∆ ABC, prove that the area

Answer:
Area of ∆ ABC is ∆ = \(\frac { 1 }{ 2 }\) bc = sin A
Using cosine formula

Question 5.
In a ∆ABC, if a = 12 cm, b = 8 cm and C = 30°, then show that its area is 24 sq.cm.
Answer:

In ∆ ABC Given
a = 12 cm ,
b = 8 cm,
C = 30°

Question 6.
In a ∆ABC, if a = 18 cm, b = 24 cm and c = 30 cm, then show that its area is 216 sq.cm.
Answer:
In a ∆ ABC, Given a = 18 cm, b = 24cm and c = 30 cm

Area of the triangle ABC

Question 7.
Two soldiers A and B in two different underground bunkers on a straighi road, spot an intruder at the top of a hill. The angle of elevation of the intruder from A and B to the ground level in the eastern direction are 30° and 45° respectively. If A and B stand 5km apart, find the distance of the intruder from B.
Answer:
Let A and B be the two positions of the soldiers.
AC – direction of the intruder seen from A.
BC – the direction of the intruder seen from B.
∠ BAC = 30° angle of elevation of the intruder from A.
∠ PBC = 45° angle of elevation of the intruder from B.

Distance between A and B = 5k.m.
In ∆ ABC, ∠ ABC = 180° – 45° = 135°
∠ BCA = 180° – ( 135° + 30°)
= 180° – 165° = 15°
Using sine formula

Question 8.
A researcher wants to determine the width of a pond from east to west, which cannot be done by actual measurement. From a point P, he finds the distance to the eastern-most point of the pond to be 8 km, while the distance to the westernmost point from P to be 6 km. If the angle between the two lines of sight is 60°, find the width of the pond.
Answer:

A – be the easternmost point on the pond and
B – be the westernmost point on the pond.
AB – Width of the pond
P – Point of observation.
The distance of A from P = 8 km
Distance of B from P = 6km
Angle between the directions PA and PB
∠APB = 60°
In ∆ PAB, using cosine formula
AB² = PA² + PB² – 2PA . PB . cos ∠APB
AB² = 8² + 6² – 2 × 8 × 6 . cos 60°
= 64 + 36 – 96 × \(\frac { 1 }{ 2 }\)
= 100 – 48 = 52
AB = \(\sqrt{52}\) = \(\sqrt{4 \times 13}\)
AB = 2\(\sqrt{13}\) k.m.
Width of the pond = 2\(\sqrt{13}\) k.m

Question 9.
Two Navy helicopters A and B are flying over the Bay of Bengal at saine altitude from sea level to search a missing boat. Pilots of both the helicopters sight the boat at the same time while they are apart 10km from each other. If the distance of the boat from A is 6 km and if the line segment AB subtends 60° at the boat, find the distance of the boat from B.
Answer:
A , B are the positions of the helicopter above the sea level.

Distance between A and B = 10 km
C – Position of the boat on the surface of sea.
AC, BC are the directions of the boat as seen from A and B respectively.
Distance of the boat C from A = 6 k.m
∠ ACB = 60°
Using cosine formula
AB² = BC² + AC² – 2 BC . AC cos ∠ACB
c² = a² + b² – 2 ab cos C
10² = a² + 6² – 2a × 6 cos 60°
100 = a² + 36 – 12a\(\left(\frac{1}{2}\right)\)
0 = a² + 36 – 6a – 100
a² – 6a – 64 = 0

Question 10.
A straight tunnel is to be made through a mountain. A surveyor observes the two extremities A and B of the tunnel to be built from a point P in front of the mountain. If AP = 3 km, BP = 5 km, and ∠APB = 120°, then find the length of the tunnel to be built.
Answer:

p² = a² + b² – 2ab cos P
p² = 9 + 25 – 30 Cos 120°
p² = 9 + 25 – 30 (-1/2) = 34 + 15 = 49
⇒ p = \(\sqrt{49}\) = 7 km

Question 11.
A farmer wants to purchase a triangular-shaped land with sides 120 feet and 60 feet and the angle included between these two sides is 60°. If the land costs Rs.500 per square feet, find the amount he needed to purchase the land. Also, find the perimeter of the land.
Answer:

Let ∆ ABC be the shape of the land.
Given AB = 120 ft, AC = 60ft
∠ BAC = 60°
Using cosine formula in ∆ ABC
BC² = AB² + AC² – 2AB . AC cos ¿BAC
BC² = 120² + 60² – 2 × 120 × 60 cos (60°)
= 14400 + 3600 – 14400 × \(\frac { 1 }{ 2 }\)
= 18000 – 7200
BC² = 10800 = 100 × 2 × 2 × 3 × 3 × 3
BC² = 10² × 2² × 3² × 3
BC = \(\sqrt{10^{2} \times 2^{2} \times 3^{2} \times 3}\)
BC = 10 × 2 × 3√3
BC = 60√3 k.m.
Perimeter of the Land = AB + BC + AC
= 120 + 60√3 + 60
= 180 + 60√3
= 60 (3 + √3) feet.
Area of ∆ ABC = \(\frac { 1 }{ 2 }\) × AB × AC × sin ∠ BAC
= \(\frac { 1 }{ 2 }\) × 60 × 120 sin 60°
= 30 × 120 × \(\frac{\sqrt{3}}{2}\)
= 30 × 60 × √3
= 1800 √3 sq. feet.
Cost of 1 sq. feet Rs. 500
∴ Cost of 800 √3 sq. feet = 800 √3 × 500 = 900000√3
Total amount needed = Rs. 900000√3
Perimeter of the land = 60(3 + √3)feet.

Question 12.
A fighter jet has to hit a small target by flying a horizontal distance. When the target is sighted, the pilot measures the angle of depression to be 30°. If after 100 km, the target has an angle of depression of 45°, how far is the target from the fighter jet at that instant?
Answer:

Let A be the position of the jet fighter observing the target at an angle of depression 30°.
Also, Let B be the position of the jet 100 k.m away horizontally from A observing the target at an angle of depression 45°.
In ∆ TAB, AB = 100 k.m
∠TAB = 30°
∠ABT = 180°- 45° = 135°
∠ATB = 180° – (135°+ 300) = 180° – 165° = 15°

Question 13.
A plane is 1 km from one landmark and 2 km from another. From the plane’s point of view, the land between them subtends an angle of 45°. How far apart are the landmarks?
Answer:
A, B are the two landmarks,
C – Position of the plane.
The distance of the plane from the landmark A = 1 k.m
The distance of the plane from the landmark B = 2 k.m
∠ACB = 45°

From the ∆ ABC, using cosine formula
AB² = AC² + BC² – 2AC. BC. cos45°
= 1² + 2² – 2 × 1 × 2
AB² = 1 + 4 – 2 × √2 = 5 – 2√2
AB = \(\sqrt{5-2 \sqrt{2}}\)
Distance between the landmarks AB = \(\sqrt{5-2 \sqrt{2}}\) km.

Question 14.
A man starts his morning walk at a point A reaches two points B and C and finally back to A such that ∠A = 60° and ∠B = 45°, AC = 4km in the ∆ ABC. Find the total distance he covered during his morning walk.
Answer:

Given In ∆ABC
AC = 4 k.m
∠A = 60°,
∠B = 45°
∠C = 180° – (60° + 45°)
∴ ∠C = 180° – 105° = 75°
Using sine formula

Question 15.
Two vehicles leave the same place P at the same time moving along two different roads. One vehicle moves at an average speed of 60 km/hr and the other vehicle moves at an average speed of 80 km/hr. After half an hour the vehicle reaches destinations A and B. If AB subtends 60° at the initial point P, then find AB.
Answer:

P – Initial point.
PA – The direction of the first vehicle travels with speed km/hr.
PB – The direction of the second vehicle travels with a speed of 80km/hr.
Given in half an hour first vehicle reaches destination A.
∴ PA = \(\frac{60}{2}\) = 30 km.
Also in half an hour the second vehicle reaches the destination B.
∴ PA = \(\frac{80}{2}\) = km.
In ∆ PAB, PA = 30, PB = 40, ∠APB = 60°
Using cosine formula
AB² = PA² + PB² – 2PA PB cos ∠APB
AB = 30² + 40² – 2 × 30 × 40 cos 60°
= 900 + 1600 – 2400 × \(\frac { 1 }{ 2 }\)
= 2500 – 1200
AB² = 1300
AB = \(\sqrt{1300}\) = \(\sqrt{13 \times 100}\)
AB = 10√13 k.m.

Question 16.
Suppose that a satellite in space, an earth station, and the centre of earth all lie in the same plane. Let r be the radius of earth and R he the distance from the centre of earth to the satellite. Let d be the distance from the earth station to the satellite. Let 30° be the angle of elevation from the earth station to the satellite, If the line segment connecting the earth station and satellite subtends angle α at the centre of earth then prove that

Answer:

O – Centre of Earth,
A – Position of Earth station.
S – Position of the satellite.
Given the radius of Earth
OA = r
The angle of elevation of the satellite from the Earth station = 30°
The distance of the satellite from the Earth station AS = d
The distance of the satellite from the centre of the Earth OS = R.
Angle subtended by the line segment AS at the centre of earth ∠AOS = α
In △ AOS, OA = r, AS = d, OS = R, ∠AOS = α
Using cosine formula
AS² = OA² + OS² – 2 OA . OS cos ∠AOS
d² = r² + R² – 2(r) (R) cos α

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 :

Answer:

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 :

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)

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

(ii)

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

2. Match the following.

Answer:
1 – d, 2 – a, 3 – b, 4 – c.

3. Match the following.

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 :

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 :

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.

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

II.

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

III.

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 12th Maths Guide Pdf Chapter 4 Inverse Trigonometric Functions Ex 4.5 Textbook Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 12th Maths Solutions Chapter 4 Inverse Trigonometric Functions Ex 4.5

Question 1.
Find the value, if it exists. If not, give the reason for non-existence.
(i) sin^-1 (cos π)
(ii) tan^-1(sin(\(\frac {-5π}{2}\)))
(iii) sin^-1 [sin 5]
Solution:
(i) sin^-1 (cos π) = sin^-1 (-1) = -sin^-1 (1) = –\(\frac {π}{2}\) [∵ cos π = -1]

(iii) sin^-1 [sin 5]
–\(\frac {π}{2}\) ≤ sin^-1 5 ≤ \(\frac {π}{2}\)
-3\(\frac {π}{2}\) ≤ 5 ≤ 2π
–\(\frac {π}{2}\) ≤ 5 – 2π ≤ 0 ≤ \(\frac {π}{2}\)
sin(5 – 2π) = sin 5
sin^-1 (sin 5) = 5 – 2π

Question 2.
Find the value of the expression in terms of x, with the help of a reference triangle.
(i) sin (cos^-1(1 – x))
(ii) cos (tan^-1 (3x – 1))
(iii) tan (sin^-1(x + \(\frac {π}{2}\)))
Solution:
(i) sin (cos^-1(1 – x)) = sin [cos^-1(adj/hyp)]

(ii) cos (tan^-1(3x – 1)) = cos [opp/adj]
Let θ = tan^-1(3x – 1)
tan θ = 3x- 1
1 + tan² θ = 1 +(3x – 1)²
sec² θ = 9x² – 6x + 2
sec θ = \(\sqrt{9x² – 6x + 2}\)
cos θ = \(\frac{1}{\sqrt{9x² – 6x + 2}}\)
⇒ cos (tan^-1(3x – 1)) = \(\frac{1}{\sqrt{9x² – 6x + 2}}\)

Question 3.
Find the value of
(i) sin^-1(cos(sin^-1(\(\frac {√3}{2}\))))
(ii) cot(sin^-1 \(\frac {3}{5}\) + sin^-1\(\frac {4}{5}\))
(iii) tan(sin^-1 \(\frac {3}{5}\) + cot^-1\(\frac {3}{2}\))
Solution:

Question 4.
(i) tan^-1\(\frac {2}{11}\) + tan^-1 \(\frac {7}{24}\) = tan^-1 \(\frac {1}{2}\)
(i) tan^-1\(\frac {3}{5}\) + cos^-1 \(\frac {12}{13}\) = sin^-1 \(\frac {16}{65}\)
Solution:

Question 5.
Prove that
tan^-1 x + tan^-1 y + tan^-1 z = tan^-1 (\(\frac {x+y+z-xyz}{1-xy-yz-zx}\))
Solution:
tan^-1 x + tan^-1 y + tan^-1 z

Question 6.
tan^-1 x + tan^-1 y + tan^-1 z = π, show that x + y + z = xyz
Solution:
tan^-1 x + tan^-1 y + tan^-1 z = π

x + y + z – xyz = 0
x + y + z = xyz

Question 7.
Prove that
tan^-1 x + tan^-1 \(\frac {2x}{1-x^2}\) = tan^-1 \(\frac {3x-x^3}{1-3x^2}\), |x| < \(\frac {1}{√3}\)
Solution:

Question 8.
Simplify
tan^-1 \(\frac {x}{y}\) – tan^-1 \(\frac {x-y}{x+y}\)
Solution:

Question 9.
(i) sin^-1 \(\frac {5}{x}\) + sin^-1 \(\frac {12}{x}\) = \(\frac {π}{2}\)
(ii) 2 tan^-1 x = cos^-1 \(\frac {1-a^2}{1+a^2}\) – cos^-1 \(\frac {1-b^2}{1+b^2}\), a > 0, b > 0
(iii) 2 tan^-1 (cos x) = tan^-1 (2 cosec x)
(iv) cot^-1 x – cot^-1 (x + 2) = \(\frac {π}{12}\), x > 0
Solution:

sin² x = sin x cos x
⇒ sin x cos x – sin² x = 0
⇒ sin x(cos x – sin x) = 0
sin x = 0 (or) cos x – sin x = 0
⇒ x = nπ, n ∈ Z, (or) cos x = sin x
tan x = 1 = tan \(\frac {π}{4}\)
⇒ x = nπ + \(\frac {π}{4}\), n ∈ Z

⇒ (x + 1)² = 4 + 2√3
⇒ (x + 1)² = 1 + 3 + 2√3
⇒ (x + 1)² = (1 + √3)²
⇒ x + 1 = 1 + √3
∴ x = √3

Question 10.
Find the number of the solutions of the equations
tan^-1(x – 1) + tan^-1 x + tan^-1(x + 1) = tan^-13x
Solution:
tan^-1(x – 1) + tan^-1 x + tan^-1(x + 1)
= tan^-1(x – 1) + tan^-1(x + 1) + tan^-1x

4x – x³ = 6x – 9x³
8x³ = 2x
8x³ – 2x = 0
2x(x² – 1) = 0
x = 0, x² = 1
x = ±1
Number of solutions are three (0, 1 -1)

Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Maths Guide Pdf Chapter 3 Trigonometry Ex 3.9 Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Maths Solutions Chapter 3 Trigonometry Ex 3.9

Question 1.
In a ∆ ABC, if \(\frac{\sin A}{\sin C}=\frac{\sin (A-B)}{\sin (B-C)}\) prove that a², b², C² are in Arithmetic progression.
Answer:
\(\frac{\sin A}{\sin C}=\frac{\sin (A-B)}{\sin (B-C)}\)
sin A . sin (B – C) = sin C . sin (A – B)
sin (180° – (B + C)) . sin (B – C) = sin (180° – (A + B)) . sin (A – B)
sin (B + C) sin (B – C) = sin (A + B) sin (A – B) ——— (1)
sin(B + C) . sin(B – C) = (sin B cos C + cos B sin C) × (sin B cos C – cos B sin C)
= (sin B cos C)² – (cos B sin C)²
= sin² B cos² C – cos² B sin² C
= sin² B (1 – sin² C) – (1 – sin² B) sin² C
= sin² B – sin² B sin² C – sin² C + sin² B sin² C
sin ( B + C) . sin ( B – C) = sin² B – sin² C
Similarly,
sin (A + B ) . sin (A – B) = sin² A – sin² B
(1) ⇒ sin² B – sin² C = sin² A – sin² B
sin² B + sin² B = sin² A + sin² C
2 sin² B = sin² A + sin² C ——— (2)

Question 2.
The angles of a triangle A B C, are in Arithmetic Progression and if b : c = √3 : √2 find ∠A.
Answer:
Given that the angles A, B, C are in A. P.
∴ 2B = A + C
Also A + B + C = 180°
B + (A + C) = 180°
B + 2B = 180°
3B = 180° ⇒ B = 60°
A + C = 2B = 2 × 60° = 120°

A + 45° = 120°
A = 120° – 45° = 75°
A = 75°

Question 3.
In a ∆ ABC, if cos c = \(\frac{\sin \mathbf{A}}{2 \sin B}\) show that the triangle is isosceles.
Answer:

a² + b² – c² = a²
b² – c² = 0
b² = c² ⇒ b = c
Two sides of is ∆ ABC are equal.
∴ ∆ ABC is an isosceles triangle.

Question 4.
In a ∆ ABC, prove that

Answer:

Question 5.
In an ∆ABC, prove that a cos A + b cos B + c cos C = 2a sin B sin C.
Answer:
LHS = a cos A+ 6 cos B + c cos C
Using sine formula, we get k sin A cos A + k sin B cos B + k sin C cos C k
= \(\frac{k}{2}\) [2 sin A cos A + 2 sin B cos B + 2 sin C cos C]
= \(\frac{k}{2}\) [sin 2A + sin 2B + sin 2C]
= \(\frac{k}{2}\) [2 sin (A + B) . cos (A – B) + 2 sin C . cos C]
= \(\frac{k}{2}\) [2 sin (A – B) . cos (A – B) + 2 sin C . cos C]
= \(\frac{k}{2}\) [2 sin C . cos (A – B) + 2 sin C . cos C]
= k sin C [cos(A – B) + cos C]

= k sin C [cos (A – B) – cos (A + B)]
= k sin C . 2 sin A sin B
= 2k sin A . sin B sin C
= 2a sin B sin C
= RHS

Question 6.
In a ∆ ABC, ∠A = 60°. Prove that b + c = 2a cos \(\left(\frac{\mathbf{B}-\mathbf{C}}{2}\right)\)
Answer:
Given ∠A = 60°
A + B + C = 180°
60° + B + C = 180°
B + C = 180° – 60° = 120°

Question 7.
In an ∆ ABC, prove the following,
(i) a sin \(\left(\frac{\mathbf{A}}{2}+\mathbf{B}\right)\) = (b + c) . sin \(\frac{\mathbf{A}}{2}\)
Answer:

(ii) a (cos B + cos C) = 2(b + c) sin²\(\frac{\mathbf{A}}{2}\)
Answer:

(iii)
Answer:

(iv)
Answer:

(v)
Answer:

Question 8.
In a triangle ∆ ABC, prove that
(a² – b² + c²) tan B = (a² + b² – c²) tan C
Answer:

Question 9.
An Engineer has to develop a triangular shaped park with a perimeter 120m in a village. The park to be developed must be of maximum area. Find out the dimensions of the park.
Answer:
Let ∆ A B C be the triangular-shaped park.
a, b, c be the length of the sides.
Given perimeter of the park = 120 m
2s = a + b + c = 120m —– (1)
For a fixed perimeter 2s. the area of a triangle is maximum when a = b = c.
(1) = a + a + a = 120
3a = 120
⇒ a = 40m
Length of the sides 40 m, 40 m, 40 rn.

Question 10.
A rope of length 42m is given. Find the largest area of the triangle formed by this rope and find the dimensions of the triangle so formed.
Answer:
Let a, b, c be the lengths of the sides of the triangle.
Given the perimeter of the triangle
2s = a + b + c = 42m —-—(1)
For a fixed perimeter 2 s, the area of a triangle is maximum
when a = b = c.
(1) ⇒ a + a + a = 42
3a = 42 ⇒ a = \(\frac{42}{3}\)
a = 14m
∴ a = b = c = 14m

∴ The dimensions of the triangle are 14 m, 14 m, 14 m.
Maximum area = 49√3 sq.m.

Question 11.
Derive Projection formula from
(i) Law of sines,
(ii) Law of cosines.
Answer:
To prove (a) a = b cos C + c cos B
(b) b = c cos A + a cos C
(c) c = a cos B + b cos A

(i) Using the Law of sines,

(a) b cos C + c cos B = 2 R sin B cos C + 2 R sin C cos B
= 2 R ( sin B cos C + cos B sin C)
= 2R sin (B + C)
= 2R sin (180° – A)
b cos C + c cos B = 2R sin A = a
a = b cos C + c cos B

(b) c cos A + a cos C = 2R sin C cos A + 2R sin A cos C
= 2R (sin C cos A + cos C sin A)
= 2R sin(C + A)
= 2R sin(180° – B)
= 2R sin B = b
∴ b = c cos A + a cos C

(c) a cos B + b cosA = 2R sin A cos B + 2R sin B cos A
= 2R (sin A cos B + cos A sin B)
= 2R sin (A + B)
= 2R sin (180° – C)
= 2R sin C = c
∴ c = a cos B + b cos A

(ii) Using Law of cosines.

Tamilnadu State Board New Syllabus Samacheer Kalvi 12th English Guide Pdf Poem 6 Incident of The French Camp Text Book Back Questions and Answers, Summary, Notes.

Tamilnadu Samacheer Kalvi 12th English Solutions Poem 6 Incident of The French Camp

12th English Guide Incident of The French Camp Text Book Back Questions and Answers

Warm Up:

Have you played chess or watched the game carefully?
Now identfy the chess pieces and complete the table below. Discuss the role of each piece in the game.

Answer:

Textual Questions:

1. Fill in the blanks choosing the words from the box given and complete the summary of the poem:

The poet Robert Browning narrates an incident at the French Camp in the war of 1809 between France and Austria, in a (a) _____ version. He describes the brave action of a (b) ______soldier, whose heroic devotion to duty and his (c) ________ in it is inspiring and worthy of (d) _____. During the attack of the French army on Ratisbon, Napoleon was anxious about the (e) _____. Austrians were defending Ratisbon with great (f) _______ and courage. Napoleon was watching the war standing on a (g) ________ near the battlefield. All of a sudden a rider appeared from the closed smoke and dust. Riding at great speed, jumping and leaping, he approached the mound where Napoleon stood. As he came closer, the narrator noticed that the rider, a young boy, was severely wounded. But the rider showed no sign of pain and smiling in joy, jumped off the horse and gave the happy news of (h) _______ to the emperor. He exclaimed with pride that French had (i) ________ Ratisbon and he himself had hoisted the flag of France. When Napoleon heard the news, his plans (j) _____ up like fire. His eyes (k) _______ when he saw that the soldier was severely wounded. Like a caring mother eagle, the emperor asked if he was wounded. The (l) _______ soldier replied proudly that he was killed and died heroically.

Answers:

(a) dramatic
(b) valiant
(c) pride
(d) admiration
(e) result
(f) determination
(g) mound
(h) victory
(i) conquered
(j) soared
(k) softened
(l) wounded

2. Based on your understanding of the poem, answer the following questions in one or two sentences each:
(Text Book Page No. 193)

Question a.
Who do you think is the narrator of the poem?
Answer:
A French soldier is the narrator of the poem.

Question b.
Where was the narrator when the incident happened?
Answer:
The narrator was in the French camp when the incident happened.

Question c.
Who took the city of Ratisbon by storm?
Answer:
French soldiers led by Marshall Lannes took the city of Ratisbon by storm.

Question d.
Where was Napoleon standing on the day of the attack on the city of Ratisbon?
Answer:
Napoleon was standing on a little mound near the battlefield.

Question e.
Describe the posture of Napoleon.
Answer:
Napoleon’s neck was outthrust. He kept his legs wide and arms locked behind as if to balance his body against his brow heavy with oppressive thoughts about the battle.

Question f.
Who came galloping on a horse to Napoleon?
Answer:
A young soldier came galloping on a horse to Napoleon.

Question g.
What does the phrase ‘full galloping’ suggest?
Answer:
Full galloping suggests full speed.

Question h.
Why was the rider in a hurry?
Answer:
The rider was in a hurry to deliver happy news of victory to his emperor.

Question i.
What did the rider do when he reached Napoleon?
Answer:
He jumped off his horse when he reached Napoleon.

Question j.
Why did the rider keep his lips compressed?
Answer:
The rider kept his lips compressed so that blood would not be visible in his mouth.

Question k.
Where did the rider plant the French flag after Ratisbon was captured?
Answer:
The rider had planted the French flag at the Market place in Ratisbon.

Question l.
What was Napoleon’s reaction to hearing the news of victory?
Answer:
Napoleon’s eyes flashed and his plans soared up like fire when he heard the news of victory.

Question m.
When did the narrator find that the boy was badly wounded?
Answer:
Soon after the boy disclosed the conquest of Ratisbon and his glorious role in perching the French flag, Napoleon found that the boy was wounded.

Question n.
Why did Napoleon’s eyes become soft as a mother eagle’s eyes?
Answer:
As Napoleon saw the young soldier severely wounded his eyes became soft as a mother eagle’s eyes.

Question o.
How did the young soldier face his end?
Answer:
The young soldier died with a smile frozen on his lips.

4. Read the lines given below and answer the questions that follow: (Text Book Page No. 194)

a) Legs wide, arms locked behind,
As if to balance the prone brow Oppressive with its mind.

i. Whose action is described here?
Answer:
Napoleon’s action is described here.

ii. What is meant by prone brow?
Answer:
The phrase ‘prone brow’ means eyebrow inclined downward.

iii. What is his state of mind?
Answer:
His state of mind is filled with anxiety and his eagerness hasted.

b) ‘You’re wounded!’ ‘Nay’, his soldier’s pride Touched to the quick, he said:

i. Why did the boy contradict Napoleon’s words?
Answer:
The boy felt proud to die for his own country. So he contradicted Napoleon’s words by saying that he was killed and not wounded.

ii. Why was his pride touched?
Answer:
His pride was touched quickly. He took pride and declared that he felt joy and thrill in giving his life for his own country.

c) A film of the mother eagle’s eye When her bruised eaglet breathes

i. Who is compared to the mother eagle in the above lines?
Answer:
Napoleon is compared to the mother eagle.

ii. Explain the comparison.
Answer:
The feelings of Napoleon at that moment were just like those of the mother eagle who gets worried and confused when she (eagle) finds her young ones badly injured and on the verge of death. Mother eagle struggles and fails to understand how to save her young one’s life. Similarly, maternal affection can be seen and felt in Napoleon’s heart when he saw that the boy was severely wounded.

iii. Why did Napoleon’s eyes become soft as a mother eaglets eyes?
Answer:
Because the soldier was severely wounded.

Additional Questions:

1) “You know, we French stormed Ratisbon A mile or so away”.

a) Who does ‘we’ refer to?
Answer:
‘We’ refer to the French people.

b) What does the word ‘stormed ‘ mean?
Answer:
The word ‘ stormed ‘ means a sudden violent attack.

2) “ On a little mound, Napoleon
Stood on our storming- day,
With neck out-thrust, you fancy how”.

a) Where was Napoleon standing?
Answer:
Napoleon was standing on a mound near the battlefield.

b) Give the meaning of ‘mound’
Answer:
hillock/hill.

3) “A rider, bound on bound Full-galloping, not bridle drew”

a) Who is the rider here?
Answer:
The rider is a young French soldier.

b) Explain full-galloping
Answer:
A young French soldier was rushing towards Napoleon riding his horse at top speed.

c) Where was the French flag planted after the victory?
Answer:
At the market area in Ratisbon.

4) “So tight he kept his lips compressed”

a) What does the word ‘compressed’ refer to?
Answer:
The word ‘compressed’ refers to pressed together.

b) Why did he keep his lips compressed?
Answer:
His mouth was full of blood so he had his lips so tightly sealed not to allow the blood to ooze out.

c) How did the young soldier face his end?
Answer:
Proudly and heroically.

5) “The chief’s eye flashed: hut presently softened itself as sheathes”

a) Whose eyes are referred to as ‘the chief’s eyes’?
Answer:
The chief’s eyes are referred to as Napoleon’s eyes.

b) Give the meaning of ‘sheathes’
Answer:
‘sheathes’ means covers.

d) Explain the following lines with reference to the context:

i. Then off there flung in smiling joy,
And held himself erect

Reference:
These lines are taken from Poem – “Incident of the French Camp”, Poet – “Robert Browning”.
Context:
The poet appreciated the heroic behaviour of the young soldier.
Explanation:
He was fatally wounded, he displayed extraordinary courage and confidence but the rider showed no sign of pain and smiling in joy.

ii. ‘I’m killed, Sire!’ And, his Chief beside,
Smiling, the boy fell dead.

Reference:
These lines are taken from Poem – “Incident of the French Camp”, Poet – “Robert Browning”.
Context:
The poet appreciated the heroic behaviour of the young soldier.
Explanation:
Napoleon became very happy about his victory, But suddenly he realised that the soldier was seriously wounded. He asked the soldier if he was wounded. The soldier replied that he was almost killed. Saying this he fell beside the emperor and died smilingly.

iii. To see your flag-bird flap his vans
Where I, to heart’s desire,
Perched him!’

Reference:
These lines are taken from Poem – “Incident of the French Camp”, Poet – “Robert Browning”.
Context:
The poet is describing the way in which the young soldier informed Napoleon of their success.
Explanation:
Due to their victory, the soldier felt a special kind of joy and pride in the fact that he, with his own hands, had flown the French flag over Ratisbon. The flag had the figure of a bird on it when the flag fluttered in the air, it seemed as the bird was flapping its wings.

5. Answer the following questions in about 100-150 words each: (Text Book Page No. 194)

Question a.
The young soldier matched his emperor in courage and patriotism. Elucidate your answer.
Question b.
What is the role of the young soldier in the victory of the French at Ratisbon?

Answer:
In “Incident of the French camp” the speaker describes a boy serving in the army of Napoleon as the army attempts to capture a city known as Ratisbon. As Napoleon stands “On a little mound”, he waits anxiously to know the outcome of the battle. Then a badly wounded young boy rides towards the emperor, jumps down from his horse, reveals that the French has taken the city, and then falls dead at Napoleon’s feet. The boy’s action can be regarded as heroic for a number of reasons.

He serves in the army, even though he is only a boy. He participates in a dangerous battle. Even though he is mortally wounded, he rides his horse at a fast gallop back to the emperor to report that the battle has been won. Even though his wounds are horrible, he behaves with great physical energy.

He calls no attention to his wounds and asks for no help. He raised the French flag in the conquered city. He takes pride in the fact that his wounds are mortal and he dies smiling. Apparently, he feels that he has served his emperor and nation and so he expresses no regrets about his death and he died heroically with a smiling face.

Question c.
Napoleon was a great source of inspiration for his army. Justify.
Answer:
The poem “Incident of the French Camp’ by Robert Browning’ narrates an actual incident in the war in 1809 between France and Austria, led by Napoleon. In this poem, the poet brings out the clear vision that Napoleon was a great source of inspiration to his army through many incidents. During the attack of the French army at Ratisbon, Napoleon was defending Ratisbon with determination. He was standing on a mound near the battlefield because he eagerly wanted to know the result of the war.

He had his neck out-thrust with legs wide and arms locked behind. It shows that he was standing majestically. Outwardly he did not reveal any sign of worry or tension. Undoubtedly, we came to know that Napoleon was a great inspiration to his army, when even a young soldier who was not in the army, worked for the country. A young French soldier got inspiration from Napoleon. He participates in a dangerous battle.

Even though he is mortally wounded, he rides his horse at a fast gallop back to the emperor to report that the battle has been won. As a king, Napoleon heard the news his plans soared up like fire. Suddenly, he became like a caring mother eagle, when he saw that the young soldier was severely wounded, He asked if he was wounded. We will surely admire the action and feeling of Napoleon who acts as a perfect king, caring and affectionate person, brave leader, etc. These all make others get inspiration from him. No doubt he was a great source of inspiration to his army and his people too.

Paragraph:

a. The young soldier matched his emperor in courage and patriotism. Elucidate your answer.
b. What is the role of the young soldier in the victory of the French at Ratisbon?
c. Napoleon was a great source of inspiration to his army. Justify.

Introduction:
The poem “Incident of the French Camp’ by Robert Browning’ narrates an actual incident in the war in 1809 between France and Austria, led by Napoleon. In this poem, the poet brings out the clear vision that Napoleon was a great source of inspiration to his army through many incidents.

The war:
During the attack of the French army at Ratisbon, Napoleon was defending Ratisbon with determination. He was standing on a mound near the battlefield because he eagerly wanted to know the result of the war. He had his neck out-thrust with legs wide and arms locked behind. It shows that he was standing majestically. Outwardly he did not reveal any sign of worry or tension. Undoubtedly, we come to know that Napoleon was a great inspiration to his army, when even a young soldier who was not in the army, worked for the country.

The arrival of the Soldiers:
A young French soldier got inspiration from Napoleon. He participates in a dangerous battle. Even though he is mortally wounded, he rides his horse at a fast gallop back to the emperor to report that the battle has been won. As a king, Napoleon heard the news his plans soared up like fire. Suddenly, he became like a caring mother eagle, when he saw that the young soldier was severely wounded, He asked if he was wounded. We will surely admire the action and feeling of Napoleon who acts as a perfect king, caring and affectionate person, brave leader, etc.

Conclusion:
These all make others get inspiration from him. No doubt he was a great source of inspiration to his army and his people too.
Greedy kills humanity.

Listening:

Some words have been left out in the poem below. First, read the poem. Then, fill in the missing words on listening to the reading or the recording of it in full. You may listen again if required:

Question 1.
The Drum – John Scott (1731—83)

I hate that drum’s _____ sound.
Parading round, and round, and round:
To thoughtless _____________ it pleasure yields,
And lures from cities and from fields,
sell their _________________ for charms
Of tawdry lace, and glittering arms;
And when________________ voice commands,
To march, and fight, and fall,
in__________.

I hate that drum’s discordant sound, parading round, and round, and round; To me, it talks of _____ plains, And burning towns and ruin’d swains, And all that Misery’s hand bestows, To fill the _____ of human woes.

Answer:
I hate that drum’s discordant sound,
Parading round, and round, and round:
To thoughtless youth it pleasures yields,
And lures from cities and from fields,
sell their liberty for charms
Of tawdry lace and glittering arms;
And when Ambition’s voice commands,
To march, and fight, and fall,
in foreign lands.

I hate that drum’s discordant sound, Parading round, and round, and round; To me it talks of ravag’d plains, And burning towns, and ruin’d swains, And all that Misery’s hand bestows, To fill the catalogue of human woes.

கவிஞரைப் பற்றி:

இராபர்ட் ப்ரௌனிங் (Robert Browning) (7 மே 1812 – 12 டிசம்பர் 1889) ஒரு ஆங்கிலக் கவிஞர் (English Poet) மற்றும் நாடக ஆசிரியர் (Play wright) ஆவார். இவர் தனது நாடக தனியுரை (dramatic monologue) மூலமாக விக்டோரியன் கவிஞர்களில் (Victorian poets) தலை சிறந்த ஒருவராகத் திகழ்ந்தார். இவர் லண்டனில் உள்ள கேம்பர்வெல் (Camberwell) என்ற குக்கிராமத்தில் மே மாதம் 7-ம் தேதி 1812-ம் ஆண்டு பிறந்தார். பெரும்பாலும் வீட்டிலேயே கற்ற இவர் கிரேக்க (Greek) மொழியை மட்டும் லண்டன் பல்கலைக்கழகத்தில் (London University) பயின்றார்.

இவரது கவிதைகள் முரண்தொடை (irony), கதாபாத்திரங்கள், இருண்ட நகைச்சுவை (dark humour), சமூக சிந்தனை (social commentary), வரலாற்றுப் பின்னணி மற்றும் மாறுபட்ட வார்த்தைகள் மற்றும் வாக்கிய கட்டமைப்புக்கு பெயர்பெற்றவை. இவர் தன் கவிதையினை தனித்தன்மை வாய்ந்த இராகமற்ற உரையாடல் வடிவில் அமைத்துள்ளார். இவரது Dramatis Personae என்ற தொகுப்பும், புத்தகம் போன்ற நீண்ட கவிதையான The Ring and the Book – ம் இவரை ஒரு தலைசிறந்த ஆங்கிலக் கவிஞராக்கியது (British Poet). இவர் ஆங்கில இலக்கியத்திற்கு அளித்துள்ள பங்கினை பாராட்டி 1881-ல் ப்ரௌனிங் இலக்கிய சமூகம் (literary society) என்ற ஒன்று அமைக்கப்பட்டுள்ளது.

கவிதையைப் பற்றி:

பண்டைய இந்தியாவிலிருந்து கணினி காலம் வரை இராணுவம் இந்த சதுரங்க விளையாட்டின் நுணுக்கங்களை உவமையாகவும் பயிற்சிக்கும் கூட பயன்படுத்தி இருக்கிறது. இந்த சதுரங்க விளையாட்டு ஆறாம் நூற்றாண்டில் ஒரு 64 கட்ட அட்டை விளையாட்டாக இந்தியாவில் தொடங்கியது. அக்காலத்திய இராணுவத்தின் ஒரு மாதிரியாக இருந்த அதனை சதுரங்கம் என்று அழைத்தனர். பாடலைக் கவனிக்கும் முன்பு இந்த சுவாரஸ்யமான பிரெஞ்சு முகாமின் நிகழ்வின் பின்னணியை பார்க்கலாம்.

நெப்போலியன் போனபாட் (1769-1821) இந்த முகாமில் ஒரு அதிகாரியாக இருந்து, இராணுவத் தளபதியாக உயர்ந்து ஒரு சிறந்த போர்வீரராகவும் இருந்து, பின்பு தனது போர்த் திறமைக்கும், புத்திக்கூர்மைக்கும் புகழ் பெற்றார். இந்த கவிதை பிரெஞ்சு முகாம் நிகழ்வு 1809 – ல் நடந்த ஒரு உண்மைச் சம்பவத்தை விவரிக்கிறது. பிரான்ஸ் (France) மற்றும் ஆஸ்திரியா (Austria) போன்ற நாடுகளுக்கிடையே நிகழ்ந்த இந்த போர் நெப்போலியன் தலைமையில் நிகழ்ந்தது. நெப்போலியன் ஒரு குன்றின் மேல் ஏறி நின்று ரேட்டிஸ் போனை (Ratisbon) எதிர் நோக்கி நிற்கிறான்.

அப்போது அவன் மனதில் பல எண்ணங்களை சுமந்து நின்றான், ஒருவேளை லேன்ஸ் ரேட்டிஸ்போனை தோற்கடிக்காவிட்டால் தன் கனவுகள் அனைத்தும் வீணாகிவிடுமே என்று தனக்குள்ளே கூறிக்கொண்டான். இந்த பாடல் பேராண்மை, துணிவு, நாட்டுப்பற்று மற்றும் தியாகம் ஒரு பிரெஞ்சு இராணுவ வீரனின் மனதில் எவ்வாறு உள்ளது என்பதை விவரிக்கிறது.

Incident of The French Camp Summary in Tamil

பிரெஞ்சுப் படையினராகிய நாங்கள் ரேட்டிஸ்போனைத் (Ratisbon நகர்) தாக்கினோம்
நெப்போலியன் ஒருமைல் தூரம் தள்ளி
ஒரு சிறிய குன்றின் (mound) மேல் ஏறி
தாக்குதல் தினத்தன்று (storming day) நின்று கொண்டிருந்தான்
தனது கழுத்தை முன் நீட்டியவாறு, (out thrust) நினைத்துப்பாருங்கள்
கால்களை அகலமாக (wide) வைத்து, கைகளை பின்னால் கட்டி, (cocked behind)
குனிய நினைக்கும் கண் இமைகளை நிலைநிறுத்தி (Pronebrow) நிற்கிறான்
தன் மனதினை எதிர்த்து (oppressive) செயல்பட நினைப்பதால்

பின் சற்று சிந்தனை (mused) எழுகிறது, என் திட்டங்கள்
உயர்கின்றன (soar), அது நிலம் நோக்கி எந்நேரமும் விழலாம் (fall),
என் படைத்தலைவன் லேன்ஸ் (lannes) அங்கிருந்த
சுவற்றில் கொடியை நாட்டியவுடன்
வேதி கொள்கலன் திறக்கப்பட்டு புகைந்தவுடன் (battery smokes)
அங்கு வருகின்றான் வீரன் துள்ளிக்குதித்து (full galloping)
முழு மூச்சில் வருகின்றான். குன்றினை அடையும் வரை
கடிவாளம் (bridle) கூட அசையவில்லை

பின் தொலைவில் தெரிந்தது மகிழ்ச்சிப் புன்னகையும் (joy)
நிமிர்ந்த (erect) உடல் தோற்றமும்
அவனது குதிரையின் முடியை (mane) மட்டும் கொண்டு, ஒரு சிறுவனாய்
உன்னாலும் சந்தேகிக்க (suspect) முடியாததாய் இருந்தது
(அவன் தன் வாயிலிருந்து குருதி வெளியேறிவிடும்
என அஞ்சி உதடுகளை இறுக்க மூடி (compressed) வைத்திருந்தான்)
நீ அவனது மார்பைக் (breast) காணும் முன் இருமுறை பார்த்தாய்.
ஆனால் அதில் இரண்டு அம்புகள் துளைத்திருந்தன (shot)

அவன் கத்தினான் அரசே (Emperor), கடவுளின் அருளால்
நாங்கள் உங்களுக்கு ரேட்டிஸ்போனை (Ratisbon) கொண்டுவந்துளோம்
மார்ஷல் (Marshall) சந்தைப் (market) பகுதியில் இருக்கின்றார்
நீங்களும் விரைவில் அங்கிருப்பீர்கள்
உமது கொடிப்பறவை (flagbird) சிறகடித்து பறப்பதை காண்பதற்கு
நான் தான் என் இதயம் கூறியதால் அவனை
அங்கிருக்க சொன்னேன் தலைவனின் கண்கள் மிளிர்ந்தன (flashed)
அவனது திட்டங்கள் காட்டுத்தீ (fire) போல் மீண்டும் உயர்ந்தன

தலைவனின் (chief) கண்கள் மிளிர்ந்தன (flashed). ஆனால் தற்போது
தன்னை வலுவிழக்கச்செய்தது தன் காயப்பட்ட குஞ்சை (bruised eaglet)
கண்ட தாய் கழுகின் (eagle) கண்கள் மறைவது போல்
அவனது கண்க ளில் மிளிர்வு குறைந்தது (softened).
உனக்கு காயம்பட்டிருக்கிறது (wounded) இல்லை (nay) அவ்வீரனின்
பெருமிதம் சட்டெனத் தொட்டது, அவன் கூறினான்
நான் கொல்லப்பட்டுவிட்டேன் (killed), தலைவரே என்று கூறி தலைவன் அருகிலேயே (beside)
சிரித்துக்கொண்ட, அவன் இறந்து விழுந்தான் (fell dead).

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 :

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:

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.

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

Question 2.

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 :

Answer:
1-c, 2 -a, 3 — e, 4-b, 5-d

II.

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.