Samacheer Kalvi 12th Physics Guide Chapter 10 Communication Systems

Tamilnadu State Board New Syllabus Samacheer Kalvi 12th Physics Guide Pdf Chapter 10 Communication Systems Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 12th Physics Solutions Chapter 10 Communication Systems

12th Physics Guide Communication Systems Text Book Back Questions and Answers

Part – I:

Textbook Evaluation:

I. Multiple Choice questions:

Question 1.
The output transducer of the communication system converts the radio signal into
a) Sound
b) Mechanical energy
c) Kinetic energy
d) None of the above
Answer:
a) Sound

Question 2.
The signal is affected by noise in a communication system
a) At the transmitter
b) At the modulator
c) In the channel
d) At the receiver
Answer:
c) In the channel

Question 3.
The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called
a) Amplitude modulation
b) Frequency modulation
c) Phase modulation
d) Pulse width modulation
Answer:
b) Frequency modulation

Question 4.
The interntionally accepted frequency deviation for the purpose of FM broadcasts.
a) 75 kHz
b) 68 kHz
c) 80 kHz
d) 70 kHz
Answer:
a) 75 kHz

Question 5.
The frequency range of 3 MHz to 30 MHz is used for
a) Ground wave propagation
b) Space wave propagation
c) Sky wave propagation
d) Satellite communication
Answer:
c) Sky wave propagation

II. Short Answers Questions:

Question 1.
Give the factors that are responsible for transmission impairments.
Answer:
Attenuation:
The strength of signal decreases with increasing distance which causes loss of energy.
Distortion:
Change in the shape of the signal
Noise:
Random or unwanted signal mixes up with the original sound.

Question 2.
Distinguish between wireline and wireless communication? Specify the range of electromagnetic waves in which it is used.
Answer:

Wireline Communication	Wireless Communication
It uses wires, cables and optical fibres as a medium	It uses free space as a medium
It cannot be used for long distance transmission	It can be used for long distance transmission
Ex. Telephone, intercom and cable TV	Ex. Mobile, radio or TV broadcasting and satellite communication

Question 3.
Explain centre frequency or resting frequency in frequency modulation.
Answer:
When the frequency of the baseband signal is zero (no input signal), there is no change in the frequency of the carrier wave. It is at its normal frequency and is called center frequency or resting frequency.

Question 4.
What does RADAR stand for?
Answer:

• RADAR stands for Radio Detection and Ranging
• It is used to sense, detect and locate distant objects like aircraft, ships, spacecraft, etc.

Question 5.
What do you mean by the Internet of Things?
Answer:
Internet of Things (IoT), it is made possible to control various devices from a single device. Example: home automation using a mobile phone.

III. Long Answers Questions:

Question 1.
What is modulation? Explain the types of modulation with necessary diagrams.
Answer:
Modulation:
For long-distance transmission, the low-frequency baseband signal (input signal) is superimposed onto a high-frequency radio signal by a process called modulation.

i) Amplitude modulation:
1. If the amplitude of the carrier signal is modified according to the instantaneous amplitude of the baseband signal.
2. The frequency and the phase of the carrier signal remains constant.
3. It is used in radio and TV broadcasting.

Advantages of AM:
1. Easy transmission and reception
2. Lesser bandwith
3. Low cost

Disadvantages of AM:
1. High noise level
2. Low efficiency
3. Small operating range

ii) Frequency modulation:
1. Frequency of the carrier signal is modified according to the instantaneous amplitude of the baseband signal.
2. The amplitude and the phase of the carrier signal remain constant.
3. Increase in the amplitude of the baseband signal increases the carrier signal frequency.
4. Louder signals form compressions and weaker signals form rarefactions.
5. When the frequency of the baseband signal is zero, there is no change in the frequency of the carrier wave. This is known as centre frequency or resting frequency.

Advantages:
1. Decrease in noise
2. Efficiency is high
3. Operating range is quite large
4. Better quality

Disadvantages:
1. Requires wider channel
2. Less area is covered.
3. Transmitters and receivers are complex and costly.

Phase Modulation:

1. The instantaneous amplitude of the baseband signal modifies the phase of the carrier signal keeping the amplitude and frequency constant.
2. The frequency shift depends on

• the amplitude of the modulating signal and
• the frequency of the signal.

3. When the modulating signal goes positive, the amount of phase lead increases with the amplitude of the modulating signal.
4. The carrier signal is compressed or its frequency is increased.
5. The negative half cycle of the baseband signal produces lag in the carrier signal.
6. Phase modulated wave also comprises of compressions and rarefactions.
7. When the signal voltage is zero, (A, C and E) the carrier frequency is unchanged.

Advantages:
1. FM Signal produced from PM signal is very stable.
2. The center frequency called resting frequency is stable.

Question 2.
Elaborate on the basic elements of a communication system with the necessary block diagram.
Answer:
1. Information (Baseband or input signal):
i. Information can be in the form of a sound signal like speech, music, pictures or computer data.
ii. These can be given as input to the input transducer.

 

2. Input transducer:
i. It converts variation in a physical quantity such as pressure, temperature, sound into equivalent electrical signals or vice versa.
ii. It converts the information into corresponding electrical signals.
iii. The electrical equivalent of the original information is called baseband signal.

3. Transmitter:
It is located at the broadcasting station.

a) Amplifier:
Very weak transducer output is amplified

b) Oscillator:
i. For long-distance, the high-frequency carrier wave is transmitted into space.
ii. Energy of the wave is proportional to its frequency, so the carrier wave has very high energy.

c) Modulator:
It superimposes the baseband signal onto the carrier signal and generates the modulated signal.

d) Power amplifier:
To cover a large distance, the power level of the electrical signal is increased.

4. Transmitting antenna:
i. It travels in the form of electromagnetic waves with the velocity of light
ii. Used for long-distance transmission
iii. Ex: Mobile, radio or TV broadcasting, satellite communication.

5. Communication channel:
To carry the electrical signal from transmitter to receiver with less noise or distortion.

Wireline Communication:
i. Medium – Wires, Cables, and optical fibers
ii. Cannot be used for long-distance transmission
iii. Ex: Telephone, intercom and Cable TV

Wireless communication:
i. Medium – free space
ii. Signals are transmitted in the form of electromagnetic waves.

6. Noise:
i. Undesirable electrical signal
ii. Reduces the quality of the transmitted signal.
iii. It may be man-made or natural.
iv. It cannot be completely eliminated but it can be reduced.

7. Receiver:
i. The transmitted signals are fed into the receiver.
ii. Receiver consists of the demodulator, amplifier, detector etc.
iii. Demodulator extracts the baseband signal from the carrier.
iv. Then it is amplified and detected, then fed to the output transducer.

8. Repeaters:
i. Combination of transmitter and receiver
ii. Increase the range or distance through which the signals are sent.
iii. Signals are received, amplified, and retransmitted with a different frequency to the destination.
iv. Ex. Communication satellite in space.

9. Output transducer:
i. Converts the electrical signal back to its original form such as sound, music, pictures or data.
ii. Ex : Loudspeakers, Picture tubes, Computer monitor etc.

10. Attenuation:
The loss of strength of a signal while propagating through a medium.

11. Range:
i. Maximum distance between the source and the destination.
ii. The signal is received with sufficient strength.

Question 3.
Explain the three inodes of propagation of electromagnetic waves through space.
Answer:
According to the frequency range, the electromagnetic wave transmitted by the transmitter travels in three different modes.

1. Ground Wave propagation (or) Surface Wave propagation:
i. The electromagnetic waves are transmitted by the transmitter glide over the surface of the earth to reach the receiver.
ii. Both transmitting and receiving antennas must be close to the earth.
iii. The size of the antenna decides the efficiency of the radiation of signals.
iv. Some reasons for attenuation are

a) Increasing distance:
Attenuation of the signal depends on
(i) Power of the transmitter
(ii) frequency of the transmitter
(iii) Condition of the earth surface.

b) Absorption of energy by the Earth:
i. Transmitted signal is in contact with the Earth, it induces charges in the Earth and constitutes a current.
ii. The Earth behaves like a leaky capacitor which leads to the attenuation of the wave.

c) Tilting of the wave:
i. The wavefront starts gradually tilting according to the curvature of the Earth.
ii. When the tilt increases, the electric field strength decreases.
iii. At some distance, the surface wave dies out due to energy loss.
iv. The frequency of the ground waves is mostly less than 2 MHz
v. It is used in local broadcasting, radio navigation, for ship – to ship, ship – to shore communication and mobile communication.

2. Skywave propagation (or) Ionospheric propagation:
i. The electromagnetic waves are radiated from an antenna, directed upwards at large angles gets reflected by the ionosphere back to earth.
ii. Due to the absorption of ultraviolet rays, cosmic ray and other high energy radiations like α, β rays from sun get ionized.
iii. These charged ions provide a reflecting medium for the reflection of radio waves.
iv. The phenomenon of bending the radio waves back to earth is due to total internal reflection.
v. The shortest distance between the transmitter and the point of reception of the skywave along the surface is called as the skip distance.
vi. When the angle of emission increases, the reception of ground waves decreases.
vii. A zone where there is no reception of electromagnetic waves neither ground nor sky is called skip zone or skip area.
viii. In this mode of propagation, the frequency range of EM waves is 3 to 30 MHz.
ix. It is used for short wave broadcast services.
x. Extremely long-distance communication is possible.
xi. A single reflection helps to travel a distance of approximately 4000 km.

3. Space Wave propagation:
i. The process of sending and receiving information signal through space.
ii. EM waves of very high frequencies above 30 MHz are used.
iii. Waves travel in a straight line from the transmitter to the receiver.
iv. The transmission towers must high.
v. For high frequencies, the signals will not encounter the curvature of the earth.
vi. It travels with less attenuation and loss of signal strength.
vii. TV broadcast, satellite communication and RADAR are based on this propagation
viii. It has some advantages, larger bandwith, high data rates, better directivity, small antenna size, low power consumption etc.
ix. Range depends on the height of the antenna (h).
x. Range or distance (d) = \(\sqrt{2 \mathrm{Rh}}\)
R – Radius of the earth
R = 6400 Km.

Question 4.
What do you know about GPS? Write a few applications of GPS.
Answer:
GPS:

1. GPS stands for Global Positioning System.
2. It offers geolocation and time information anywhere on or near the earth.
3. It works with the assistance of a satellite network.
4. It broadcasts a precise signal like an ordinary radio signal.
5. It convey the location data which is translated by the GPS software.
6. This software recognize the satellite, its location ahd time taken to travel from each satellite.
7. Then the data from each satellite is processed to estimate the location of the receiver.

Applications:

1. It is used in fleet vehicle management for tracking cars, trucks and buses.
2. In wildlife management for counting of wild animals.
3. In engineering for making tunnels, bridges etc.

Question 5.
Give the applications of ICT is mining and agriculture sectors.
Answer:
ICT in mining:

1. Improves operational efficiency, remote monitoring and disaster locating system.
2. Provides audio – visual warning to the trapped underground miners.
3. Helps to connect remote sites.

ICT in agriculture:

1. Increases food productivity and farm management.
2. Optimize the use of water, seeds and fertilizers etc.
3. It is used in farming to decides the suitable place for the species to be planted.
4. It can be used in sophisticated technologies like robots, temperature, moisture sensors, aerial images and GPS technology.

Question 6.
Modulation helps to reduce the antenna size in wireless communication Explain.
Answer:

1. Antenna is used at both transmitter and receiver.
2. Antenna height is important in wireless communication.
3. The height of the antenna must be a muiltiple of \(\frac{\lambda}{4}\).
   i.e h = \(\frac{\lambda}{4}\)
   Where, λ = \(\frac{C}{\gamma}\), C = Velocity of light
   γ – frequency λ – wavelength
4. Consider two base band signals.
5. One is modulated and the other is not modulated
6. Frequency of the original baseband signal, γ = 10 KHz
7. Frequency of the modulated signal, γ = 1 MHz
8. Height required to transmit the original baseband signal is,
   h₁ = \(\frac{\lambda}{4}=\frac{C}{4 \gamma}\)
   = \(\frac{3 \times 10^{8}}{4 \times 10 \times 10^{3}}\) = 7.5 Km
   Height required to transmit the modulated signal is
   h₂ = \(\frac{\lambda}{4}=\frac{C}{4 \gamma}\)
   = \(\frac{3 \times 10^{8}}{4 \times 10 \times 10^{6}}\) = 75 m
9. From the above example, it is clear that modulated signals reduce the height of the antenna.

Question 7.
Fiber-optic communication is gaining popularity among the various transmission media – justify.
Answer:
The method of transmitting information from one place to another in terms of light pulses through an optical fiber is called fiber optic communication. It is in the process of replacing wire transmission in communication systems. Light has very high frequency (400 THz – 790 THz) than microwave radio systems.  The fibers are made up of silica glass or silicon dioxide which is highly abundant on Earth.

Now it has been replaced with materials such as chalcogenide glasses, fluoro aluminate crystalline materials because they provide larger infrared wavelength and better transmission capability. As fibers are not electrically conductive, it is preferred in places where multiple channels are to be laid and isolation is required from electrical and electromagnetic interference.

Applications:
Optical fiber system has a number of applications namely, international communication, inter-city communication, data links, plant and traffic control and defense applications.

Merits:

1. Fiber cables are very thin and weight lesser than copper cables.
2. This system has much larger bandwidth. This means that its information-carrying capacity is larger.
3. Fiber optic system is immune to electrical interferences.
4. Fiber optic cables are cheaper than copper cables.

Demerits:

1. Fiber optic cables are more fragile when compared to copper wires.
2. It is an expensive technology.

PART – II:

12th Physics Guide Communication Systems Additional Questions and Answers

I. Matching Type Questions:

Question 1.

Column 1	Column 2
1. Wireless communication	a. 30 MHz to 400 GHz
2. Ground wave propagation	b. 3 MHz to 30 GHz
3. Sky wave propagation	c. 2 KHz to 2 MHz
4. Space wave propagation	d. 2 KHz to 400 GHz

Answer:

1. d
2. c
3. b
4. a

Question 2.

Column 1	Column 2
1. GPS	a. Fisheries
2. GSM	b. Military and Navigation systems
3. ICT	c. Mobile communication
4. RADAR	d. Counting of wild animals

Answer:

1. d
2. c
3. a
4. b

Question 3.

Column 1	Column 2
1. Uplink Frequency band	a. 20 – 20,000 Hz
2. Downlink Frequency band	b. 400 THz – 790 THz
3. Very High frequency of light	c. 6 GHz
4. Audio frequency	d. 4 GHz

Answer:

1. c
2. d
3. b
4. a

II. Fill in the blanks:

Question 1.
_______ gives the difference between the upper and lower frequency limits of the signal.
Answer:
Bandwidth

Question 2.
For a frequencv less than the critical frequencv, skip distance is _______.
Answer:
Zero

Question 3.
Multimode fibers operate at the speed of _______.
Answer:
10 Mbps

Question 4.
Radar uses _______ for communication.
Answer:
electromagnetic waves.

III. Choose the Odd man out:

Question 1.
a) Input transducer
b) Amplifier
c) Oscillator
d) Demodulator
Answer:
d) Demodulator

Question 2.
a) Telephone
b) mobile
c) intercom
d) Cable TV
Answer:
b) Mobile

Question 3.
a) Weather satellites
b) Communication
c) satellites
d) Navigation satellites
e) RADAR
Answer:
e) RADAR

Question 4.
a) Total internal reflection
b) skip distance
c) amplitude modulation
d) skip zone
Answer:
c) Amplitude modulation

IV. Choose the incorrect pair:

Question 1.
i) Space wave propagation – LOS
ii) Tracking cars – ICT
iii) Counting of wild animals – GPS
iv) Home automation using
a mobile phone – IoT
Answer:
ii) Tracking cars – ICT

Question 2.
i) Input transducer – Microphone
ii) Output transducer – Loudspeakers
iii) Transmitter – Broadcasting station
iv) Oscillator – Low-frequency carrier wave
Answer:
iv) Oscillator – Low-frequency carrier wave

Question 3.
i) Bandwidth, BW – γ₁ – γ₂
ii) Amplitude modulation system – 10 KHz
iii) Single side – band system – 5 KHz
iv) Height of the Antenna – \(\frac{\lambda}{4}\)
Answer:
i) Bandwidth, BW – γ₁ – γ₂

Question 4.
i) Amplitude – High-efficiency modulation
ii) Baseband signal – input signal
iii) Carrier signal – a radio signal
iv) Resting frequency – centre frequency
Answer:
i) Amplitude modulation – High efficiency

V. Choose the correct pair:

Question 1.
i) Attenuation – Amplitude of the transmitter
ii) High frequency – High skip distance
iii) Skip distance – The longest distance
iv) RADAR – Ground wave propagation
Answer:
ii) High frequency – High skip distance

Question 2.
i) Audio frequency – 200 to 2000 Hz
ii) Carrier wave – Cosine wave
iii) Louder signal – Compressions
iv) Frequency shift – Rarefaction
Answer:
iii) Louder signal- Compressions

Question 3.
i) Velocity of light – 3 × 10⁶ m/ s
ii) Radius of the earth – 6800 Km
iii) Date speed for homes – 2 Gbps
iv) Antenna height – d = \(\sqrt{2 \mathrm{Rh}}\)
Answer:
iv) Antenna height – d = \(\sqrt{2 \mathrm{Rh}}\)

Question 4.
i) Skywave propagation – 3 MHz to 30 MHz
ii) Space wave propagation – 30 MHz to 40 MHz
iii) Ground wave propagation – 20 KHz to 20 MHz
iv) Wireless communication – 1 KHz to 2 KHz
Answer:
i) Skywave propagation – 3 MHz to 30 MHz

VI. Assertion and Reason:

Question 1.
Assertion:
Short wave bands are used for the transmission of radio waves to a large distance.
Reason:
Short waves are reflected by the ionosphere.
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.
b) Assertion and the reason are true and the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false
d) Assertion is false but reason is true.
Answer:
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.

Question 2.
Assertion:
Television broadcasting becomes weaker with increasing distance.
Reason:
The power transmitted from the TV transmitter varies inversely as the distance of the receiver.
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.
b) Assertion and the reason are true and the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false
d) Assertion is false but reason is true.
Answer:
c) Assertion is true but reason is false

Question 3.
Assertion:
Optical fibre communication has immunity to cross talk.
Reason:
Optical interference between fibres is zero.
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.
b) Assertion and the reason are true and the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false
d) Assertion is false but reason is true.
Answer:
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.

Question 4.
Assertion:
A dish antenna is highly directionals
Reason:
This is because a dipole antenna is omnidirectional.
a) Assertion and the reason are true and the reason is the correct explanation of the assertion.
b) Assertion and the reason are true and the reason is not the correct explanation of the assertion.
c) Assertion is true but reason is false
d) Assertion is false but reason is true.
Answer:
b) Assertion and the reason are true and the reason is not the correct explanation of the assertion.

VII. Choose the correct statement:

Question 1.
i) A transducer is a device which converts an electrical signal into variations in a physical quantity.
ii) Transmitting antenna radiates the radio signal into space in all directions.
iii) The power amplifier decreases the power level of the signal
iv) The minimum distance between the source and the destination is called a range
Answer:
Statement (ii) is correct.

Question 2.
i) Attenuation depends on the frequency of the transmitter.
ii) Increase in the tilt increases the electric field strength.
iii) Transmitting and receiving antenna must be close to the earth.
iv) The frequency of the ground waves is most less than 1 MHz.
Answer:
Statements (i) and (iii) are correct

Question 3.
i) The higher the frequency, lower is the skip distance.
ii) Bending of radio waves back to earth is called refraction.
iii)The frequency range of EM wave in skywave propagation is 30 to 300 MHz.
iv) When the angle of emission increases, the reception of ground waves decreases.
Answer:
Statement (iv) is correct.

Question 4.
i) The transducer output is very weak
ii)The electrical equivalent of the original information is called the carrier signal.
iii) Microphone converts electrical energy into sound energy.
iv) Wireline communication uses free space as a communication medium.
Answer:
Statement (i) is correct.

VIII. Choose the incorrect statement:

Question 1.
i) Noise is the undesirable electrical signal.
ii) It attenautes or reduces the quality of the signal
iii) It may be man – made or natural
iv) Noise can be completely eliminated.
Answer:
Statement (iv) is correct.

Question 2.
i) Operating range is quite large in FM
ii) In FM, there is a large increase in noise
iii) Am radio has better quality compared to FM radio.
iv) FM requires a much under channel
Answer:
Statement (ii) & (iii) are incorrect

Question 3.
i) Noise level is low in AM
ii) There is a lesser landwidth in AM
iii) In A.M the efficiency is low
iv) Small operating range in AM
Answer:
Statement (i) is incorrect

Question 4.
i) ICT in mining helps to connect remote sites.
ii) ICT is widely used in decreasing food productivity
iii) ICT improves operational efficiency
iv) ICT are also used in fisheries
Answer:
Statement (ii) is incorrect

IX. Choose the best answer:

Question 1.
Which of the following frequencies will be suitable for beyond the horizon communication using sky waves?
(a) 10 kHz
(b) 10 MHz
(c) 1 GHz
(d) 1000 GHz
Answer:
(b) 10 MHz
Hint:
A frequency of 10 kHz will require a very large radiating antenna while frequencies 1GHz and 1000 GHz will penetrate the ionosphere and cannot be reflected by it.

Question 2.
Cellular phones use radio waves in ______ band.
a) long-wave
b) short wave
c) medium wave
d) ultra-high frequency
Answer:
d) ultra-high frequency

Question 3.
Antenna is
(a) inductive
(b) capacitive
(c) resistive above its resonant frequency
(d) resistive at the resonant frequency
Answer:
(d) resistive at the resonant frequency.
Hint:
An antenna is a tuned circuit consisting of an inductance and a capacitance. At the resonant frequency, it is resistive.

Question 4.
In space wave propagation, the range of the propagation depends on the height (h) of the antenna given by the equation.
a) \(\sqrt{2 \mathrm{Rh}}\)
b) \(\sqrt{\frac{R h}{2}}\)
c) \(\sqrt{2 R^{2} h}\)
d) \(\frac{h}{2 R}\)
Answer:
a) \(\sqrt{2 \mathrm{Rh}}\)

Question 5.
_______ modulation is used in radio and TV broadcasting.
a) Frequency
b) Phase
c) Amplitude
d) Carrier
Answer:
c) Amplitude

Question 6.
If a ________ wave is used as the baseband signal, then phase reversal takes place in the modulated signal.
a) Square
b) Sine
c) Cosine
d) triangular
Answer:
a) Square

Question 7.
An oscillator is producing FM waves of frequency 2 kHz with a variation of 10 kHz. What is the modulation index?
(a) 0.67
(b) 5.00
(c) 0.20
(d) 1.5
Answer:
(b) 5.00
Hint:
m_f = \(\frac { ∆f }{ f }\) = \(\frac { 10kHz }{ 2kHz }\) = 5

Question 8.
The best example of transducer is________
a) Loudspeaker
b) picture tubes
c) computer monitor
d) microphone
Answer:
d) microphone

Question 9.
________ generates high – frequency carrier wave.
a) Modulator
b) Oscillator
c) Amplifier
d) Power amplifier
Answer:
b) Oscillator

Question 10.
The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to
(a) h^1/2
(b) h
(c) ^3/2
(d) h²
Answer:
(a) h^1/2
Hint:
d = \(\sqrt { 2Rh } \) ; d ∝ h^1/2

Question 11.
The height of the antenna must be a multiple of _______.
a) \(\frac{\lambda}{4}\)
b) \(\frac{\lambda}{8}\)
c) 4λ
d) 2λ
Answer:
a) \(\frac{\lambda}{4}\)

Question 12.
The relation between the frequency, the velocity of light, and wavelength is given by ________.
a) C = γλ
b) C = \(\frac{\lambda}{\gamma}\)
c) λ = \(\frac{C}{\gamma}\)
d) both (a) and (c)
Answer:
d) both (a) and (c)

Question 13.
In AM, the channel bandwidth is ______ the signal frequency
a) thrice
b) twice
c) equal to
d) half
Answer:
b) twice

Question 14.
The height of the transmitting and receiving antenna must be a multiple of
a) 2λ
b) λ/4
c) λ/2
d) 4λ
Answer:
b) λ/4

Question 15.
A laser beam is used for carrying out surgery because it
(a) is highly monochromatic
(b) is highly coherent
(e) is highly directional
(d) can be sharply focused
Answer:
(d) can be sharply focused
Hint:
A laser beam is highly monochromatic, directional, and coherent and hence it can be sharply focused for carrying out surgery.

Question 16.
The _______ of the antenna plays a major role in deciding the efficiency of the radiation of the signals.
a) shape
b) distance
c) direction
d) size
Answer:
d) size

Question 17.
A single reflection helps the radio waves to travel a distance of approximately
a) 40 km
b) 400 km
c) 4000 km
d) 4 km
Answer:
c) 4000 km

Question 18.
When the angle of emission increases, the reception of ground waves _______.
a) increases
b) decreases
c) remains constant
d) none of the above
Answer:
b) decreases

Question 19.
The principle used in the transmission of signals through an optical fiber is
(a) total internal reflection
(b) refraction
(c) dispersion
(d) interference
Answer:
(a) total internal reflection
Hint:
Signals propagate through an optical fiber by suffering repeated total internal reflections.

Question 20.
The fibres are made up of _______.
a) glass
b) silicon
c) silica glass
d) both a & c
Answer:
d) both a & c

Question 21.
_______ provide the fastest transmission rate compared to any other form of transmission
a) Cable wires
b) Fibers
c) Fiber optic cables
d) Copper wire
Answer:
c) Fiber optic cables

Question 22.
________ is a fast-growing technology in the field communication system.
a) Mobile
b) Satellite
c) Fiber optics
d) Internet
Answer:
d) Internet

Question 23.
The skywave propagation is suitable for radio waves of frequency
(a) from 2 MHz to 50
(b) upto 2MHz
(c) from 2 MHz to 30 MHz
(d) from 2MHz to 20 MHz
Answer:
(c) from 2 MHz to 30 MHz

Question 24.
To store all the information available on the internet, we need over
a) 2 billion DVDs
b) 1 billion DVDs
c) 3 billion DVDs
d) 4 billion DVDs
Answer:
b) 1 billion DVDs

Question 25.
_______ is used to search for information on the World Wide Web
a) Communication
b) Satellite
c) E-Commerce
d) Search engine
Answer:
d) Search engine

Question 26.
_______ is used for making tunnels, bridges etc.
a) GSM
b) TDMA
c) GPS
d) GPRS
Answer:
c) GPS

Question 27.
Fiber optic cables provide data speed of ____ for homes and businesses.
a) 1 Gbps
b) 2 Gbps
c) 10 Mbps
d) 5 Gbps
Answer:
a) 1 Gbps

Question 28.
A modem is a device which performs
(a) modulation
(b) demodulation
(c) rectification
(d) modulation and demodulation
Answer:
(d) modulation and demodulation

X. Two Marks Questions:

Question 1.
What is a communication system?
Answer:
The setup used to transmit information from one point to another is called a communication system.

Question 2.
What is called a baseband signal?
Answer:
The electrical equivalent of the original information.

Question 3.
What is a transducer?
Answer:
A device that converts variations in a physical quantity into an equivalent electrical signal.

Question 4.
Define bandwidth.
Answer:
The frequency range over which the baseband signals or the information signals such as voice, music, the picture is transmitted.

Question 5.
Define bandwidth?
Answer:
The frequency range over which the baseband signals or the information signals such as voice, music, picture, etc. is transmitted is known as bandwidth.

Question 6.
What is skip distance?
Answer:
The shortest distance between the transmission and the point of reception of the skywave along the surface.

Question 7.
What is skip zone or skip area?
Answer:

• The zone in which there is no reception of electromagnetic waves.
• It is also called as skip area.

Question 8.
What is called fibre optic communication?
Answer:
The method of transmitting information from one place to another in terms of light pulses through an optical fiber.

Question 9.
What is mean by fibre optic communication?
Answer:
The method of transmitting information from one place to another in terms of light pulses through an optical fiber is called fiber optic communication.

Question 10.
Expand GPS and write a note on it.
Answer:

• GPS stands for Global Positioning System.
• It is a global navigation satellite system that offers geolocation and time anywhere on or near the earth.

Question 11.
Why do we need carrier waves of very high frequency in the modulation of signals?
Answer:
High-frequency carrier waves are used

1. to increase operating range
2. to reduce antenna length
3. to convert the wideband signal into the narrowband signal.

Question 12.
Why is modulation needed at all?
Answer:
Modulation is needed.

1. to transmit a low-frequency signal to a distant place.
2. for protecting the waveform of the signal
3. to keep the height of antenna small.

Question 13.
Which is better for high fidelity reception FM or AM?
Answer:
FM transmission gives high fidelity due to the presence of a large number of sidebands.

Question 14.
Why is the transmission of signals through a coaxial cable not possible for frequencies greater than 20 MHz?
Answer:
For frequencies greater than 20 MHz, dielectric loss becomes quite high.

Question 15.
Why are short wave bands used for long-distance transmission of signals?
Answer:
Radio waves of short wave bands can be easily reflected bv the ionosphere. So they are used in long-distance transmission.

Question 16.
Why microphone is used as an input transducer?
Answer:
A transducer is a device that converts sound into an equivalent electrical signal So, a microphone which converts sound into electrical energy is used as a transducer.

Question 17.
What are the elements in the transmitter?
Answer:

1. Amplifier
2. Modulator
3. Oscillator
4. Power amplifier

Question 18.
Draw the block diagram of Transmission.
Answer:

Question 19.
Define range.
Answer:
The maximum distance between the source and the destination upto which the signal is received with sufficient strength.

Question 20.
Mention the application of ICT is fisheries.
Answer:

• Satellite vessel monitoring system helps to identify fishing zones.
• Use of barcodes helps to identify time and date of catch, species name, quality of fish.

Question 21.
What is satellite communication?
Answer:
A mode of communication of signal between transmitter and receiver via satellite.

Question 22.
What are the basic elements required for the transmission and reception of a signal?
Answer:
Transducer, amplifier, carrier signal, modulator, power amplifier, medium of transmission, tansmitting and receiving antenna, demodulator and detector.

Question 23.
Give the reasons for attenuation in the Ground wave propagation.
Answer:

1. Increasing distance
2. Absorption of energy by the earth
3. Tilting of the wave.

XI. Three Marks questions:

Question 1.
What are the advantages of FM?
Answer:

1. Large decrease in noise. An increase in signal noise ratio
2. The operating range is quite large
3. The transmission efficiency is very high
4. FM bandwidth covers the entire frequency range.
5. FM radio has better quality compared to AM radio.

Question 2.
What are the disadvantages of FM?
Answer:

1. FM requires a much wider channel
2. FM transmitters and receivers are more complex and costly.
3. In FM reception, less area is covered compared to AM.

Question 3.
Give the reason why transmission of TV signals via sky wave is not possible.
Answer:

1. Television frequencies lie in the range 100 – 220 MHz which cannot be reflected by the ionosphere.
2. So, sky wave propgation is not used in TV transmission.

Question 4.
Show in diagram, the skip distance and the skip zone.
Answer:

Question 5.
It is necessary to use satellites for long distance TV transmission. Why?
Answer:

1. TV signals being of high frequency are not reflected by the ionosphere.
2. Ground wave transmission is possible only up to a limited range.
3. So, satellites are used for long distance TV transmission.

Question 6.
Which is more efficient mode of transmission FM or AM?
Answer:

1. FM transmission is more efficient because all the transmitted power is useful.
2. In AM transmission, most of the power goes waste in transmitting the carrier alone.

Question 7.
Give an account of E-commerce and search engine.
Answer:
E-Commerce:
Buying and selling of goods and services, transfer of funds are done by an electronic network.
Search engine:
A web-based service tool used to search for information on World Wide Web.

Question 8.
Expand GSM. Give a note on it.
Answer:

• GSM – Global System for Mobile Communication.
• Increases the utilization of bandwidth of the network, sharing of the networks, error detections etc.

Question 9.
Mention some of the applications of optical fiber system.
Answer:

1. International Communication
2. Intercity communication
3. data links
4. plant and traffic control
5. defence applications.

Question 10.
What are repeaters in an electronic communication system?
Answer:

1. Repeaters are a combination of transmitter and receivers.
2. Used to increase the range or distance through which the signals are sent.
3. The received signals are transmitted with a carrier signal of different frequencies to the destination.

Question 11.
State two factors by which the range of transmission of T.V. signals can be increased.
Answer:
The range of TV transmission can be increased by using

• tall antenna and
• geostationary satellites.

Question 12.
Compare the difference between PM and FM.
Answer:

Phase Modulation	Frequency Modulation
1. Smaller bandwidth	Larger bandwidth
2. High transmission speed	Low transmission speed
3. More information can be sent.	Less information can be sent

Question 13.
Why should transmitters broadcasting programmes use different carrier frequencies?
Answer:

1. Different audio signals fall in the same spectral range.
2. Different transmitting stations are allowed different slots in radio frequency range.
3. A single receiver can tune into these frequencies without any confusion or overlap.

Question 14.
Give one example each of a system that uses the (i) sky – wave (ii) space wave mode of propagation.
Answer:

1. Short broadcast services use skywave propagation.
2. TV broadcast, microwaves links, satellite communication use space wave propagation.

Question 15.
A transmitting antenna has a height of 40m and the height of the receiving antenna is 30m. What is the maximum distance between them for line-of-sight communication?
[The radius of the earth is 6.4 × 10⁶ m]
Solution:
The total distance d between the transmitting and receiving antennas will be the sum of the individual distances of coverage,
d = d₁ + d₂
= \(\sqrt{2 R}\left(\sqrt{h_{1}}+\sqrt{h_{2}}\right)\)
= \(\sqrt{2 \times 6.4 \times 10^{6}}\)
= 16 × 10²√5 × (6.32+ 5.48)
= 42217m
d = 42.217 km

XII. Five Mark Questions:

Question 1.
Explain mobile communication? Write its applications.
Answer:
Mobile communication is used to communicate with others in different locations without the use of any physical connection like wires or cables. It allows the transmission over a wide range of area without the use of the physical link. It enables people to communicate with each other regardless of a particular location like office, house, etc. It also provides communication access to remote areas.

It provides the facility of roaming:
that is. the user may move from one place to another without the need of compromising on the communication. The maintenance and cost of installation of this communication network are also cheap.

Applications:

1. It is used for personal communication and cellular phones offer voice and data connectivity with high speed.
2. Transmission of news across the globe is done within a few seconds.
3. Using the Internet of Things (IoT), it is made possible to control various devices from a single device.
   Example: home automation using a mobile phone.
4. It enables smart classrooms, online availability of notes, monitoring student activities etc. in the field of education.

Question 2.
Give a brief account on RADAR and its applications.
Answer:

1. RADAR stands for Radio Detection and Ranging system.
2. The angle, range or velocity of the objects which are invisible to the human eye can be determined.
3. Electromagnetic waves are used for communication.
4. Signal is initially radiated into space by an antenna in all direction.
5. Then it gets reflected or reradiated in many directions as it strikes the object.
6. Radar antenna receives the reflected radio signal and it is delivered to the receiver.
7. These signals are processed and amplified to determine the geographical statistics of the object.
8. the range is determined by calculating the time taken by the signal to travel from RADAR to the target and back.

Applications:
RADAR is used

1. to sense, detect and distant objects like aircraft, ships, spacecraft etc.
2. in military for locating and detecting the targets.
3. in navigation systems such as ship-borne surface search, air search and weapons guidance system.
4. to measure precipitation rate and wind speed in meteorological observation
5. to locate and rescue people in emergency situations.

Question 3.
What do you know about mobile communication? Give its applications.
Answer:

1. Mobile communication is used to communicate with others in different locations without the use of any physical connection like wires or cables.
2. It allows the transmission over a wide range of areas without the use of the physical link.
3. It also provides communication access to remote areas.
4. It provides the facility of roaming.
5. User may move from one place to another without the need of compromising on the communication.
6. The maintenance and cost of installation are cheap.

Applications:

1. It is used to communicate with each other regardless of a particular location like office, house etc.
2. It is used for personal communication.
3. Cellular phones offer voice and data connectivity with high speed.
4. Transmission of news across the globe is done within a few seconds.
5. IoT is used to control various devices from a single device
   Ex. home automation using a mobile phone.
6. It enables smart classrooms, online availability of notes, monitoring student activities etc in the field of education.

Question 4.
What is bandwidth? Explain the bandwidth of the transmission system.
Answer:

1. The frequency range over which the baseband signals or the information signals such as voice, music, picture, etc is transmitted.
2. Each of these signals has different frequencies. The communication system depends on the nature of the frequency band for a given signal.
3. Bandwidth gives the difference between the upper and lower frequency limits df the signal.
4. The portion of the electromagnetic spectrum occupied by the signal.
5. If γ₁ and γ₂ are the lower and upper-frequency limits of a signal.
6. Bandwidth, BW = γ₂ – γ₁

Bandwidth of Transmission system:

1. The range of frequencies required to transmit a piece of specified information in a particular channel.
2. An amplitude modulation system requires a channel bandwidth of 10 kHz to transmit a 5 kHz signal.
3. A single side-band system requires only 5 kHz channel bandwidth for a 5 kHz signal.
4. Because in amplitude modulation, the channel bandwidth is twice the signal frequency.
5. It is required to reduce the channel bandwidth to accommodate more channels in the available electromagnetic spectrum.

Question 5.
Explain the process of modulation.
Answer:

1. For long-distance transmission, the low-frequency baseband signal is superimposed onto a high-frequency radio signal.
2. The energy of the information signal is sufficient to send directly.
3. A very high-frequency signal called carrier signal is used to carry the baseband signal.
4. As the frequency of the carrier signal is very high, it can be transmitted to long distances with less attenuation.
5. The carrier wave is a sine wave signal.
6. The carrier signal will be more compatible.
7. It propagates in free space with greater efficiency.
8. A sine wave can be represented as
   e_c = E_c sin (2πγ_ct + φ)
   Where, E_c – amplitude γ_c – frequency
   φ – the initial phase of the carrier wave at time ‘t’
9. The characteristics of the carrier signal are modified in three types.
   • Amplitude modulation
   • Frequency modulation
   • Phase modulation.

Question 6.
What do you know about INTERNET? Write its few applications?
Answer:
Internet is a fast-growing technology in the field of a communication system with multifaceted tools. It provides new ways and means to interact and connect with people. Internet is the largest computer network recognized globally that connects millions of people through computers. It finds extensive applications in all walks of life.

Applications:

1. Search engine: The search engine is basically a web-based service tool used to search for information on World Wide Web.
2. Communication: It helps millions of people to connect with the use of social networking: emails, instant messaging services, and social networking tools.
3. E-Commerce: Buying and selling of goods and services, transfer of funds are done over an electronic network.