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NEET • PHYSICS • COMMUNICATION SYSTEMS

Communication systems practice · Mixed difficulty

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Showing 1-30 of 44 questions

1 Easy

1 of 44

Understanding +4 | -1

In the communication systems, AM is used for broadcasting because

View answer and explanation

Correct option: A

Its use avoids receiver complexity

Option A (Its use avoids receiver complexity) is the reason AM is used for broadcasting, as it simplifies the design and cost of receivers.

2 Easy

2 of 44

Application +4 | -1

The maximum and minimum voltage of an amplitude modulated signal are

60 \mathrm{~V}

and

20 \mathrm{~V}

respectively. The percentage modulation index will be:

View answer and explanation

Correct option: B

50 \%

Option B (50%) is correct because the percentage modulation index is calculated as ((Vmax - Vmin) / (Vmax + Vmin)) * 100.

3 Easy

3 of 44

Remembering +4 | -1

Depth of modulation

\left( {{m_a}} \right)

in terms of

{{\text{E}}_{{\text{max}}}}\,{\text{and}}\,{{\text{E}}_{{\text{min}}}}

View answer and explanation

Correct option: C

{{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}

Option C,

{{\text{m}}_{\text{a}}}{\text{ = }}{{\text{E}}_{{\text{max}}}}{\text{ - }}{{\text{E}}_{{\text{min}}}}{\text{/}}{{\text{E}}_{{\text{max}}}} + {{\text{E}}_{{\text{min}}}}

, is the correct formula for calculating the depth of modulation (

m_a

) in terms of the maximum and minimum amplitudes of the modulated wave.

4 Easy

4 of 44

Remembering +4 | -1

The process of superimposing signal frequency (i.e., audio wave) on the carrier wave is known as

View answer and explanation

Correct option: C

Modulation

Option C (Modulation) is correct because modulation is the process of superimposing a signal onto a carrier wave.

5 Hard

5 of 44

Application +4 | -1

The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.93 A when the carrier is modulated by single sine wave. Find the percentage modulation.

View answer and explanation

Correct option: B

0.701

Option B (0.701) is correct because it represents the modulation index calculated from the antenna currents with and without modulation.

6 Easy

6 of 44

Application +4 | -1

An audio signal of amplitude one half the carrier amplitude is used in amplitude modulation. Calculate the modulation index?

View answer and explanation

Correct option: A

0.5

Option A (0.5) is correct because the modulation index is the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

7 Easy

7 of 44

Understanding +4 | -1

When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity

ie

, dielectric constant dielectric constant of the ionised layer

View answer and explanation

Correct option: C

Appears to decrease

The correct answer is C (Appears to decrease) because the refractive index of the ionosphere is related to the electron density, and as electromagnetic waves enter, the effective dielectric constant decreases.

8 Medium

8 of 44

Remembering +4 | -1

Frequency range for microwaves is

View answer and explanation

Correct option: D

1 \times {10^9}\,to\,3 \times {10^{11}}\,Hz

Option D (

1 \times {10^9}\,to\,3 \times {10^{11}}\,Hz

) is correct because it represents the standard frequency range allocated for microwave radiation.

9 Easy

9 of 44

Understanding +4 | -1

In frequency modulated wave

View answer and explanation

Correct option: A

Frequency varies with time

The correct answer is A (Frequency varies with time) because, by definition, in frequency modulation, the frequency of the carrier wave is varied according to the message signal.

10 Medium

10 of 44

Understanding +4 | -1

In amplitude modulation, the bandwidth is

View answer and explanation

Correct option: A

Twice the audio signal frequency

Option A (Twice the audio signal frequency) is correct because in Amplitude Modulation (AM), the bandwidth is twice the highest frequency component of the modulating audio signal.

11 Medium

11 of 44

Analyzing +4 | -1

Assertion: Amplitude modulation shows more interference than frequency modulation with noise.
Reason: Interference is function of amplitude of modulation wave with carrier wave.

View answer and explanation

Correct option: B

If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion

Option B is correct because both the assertion and the reason are true, but the reason does not fully explain the assertion.

12 Medium

12 of 44

Understanding +4 | -1

Consider telecommunication through optical fibres. Which of the following statements is no true?

View answer and explanation

Correct option: B

Optical fibres are subjected to electro-magnetic interference from outside

Option B (Optical fibres are subjected to electro-magnetic interference from outside) is not true because optical fibers use light signals, which are immune to electromagnetic interference.

13 Hard

13 of 44

Application +4 | -1

Calculate the phase velocity of electromagnetic wave having electron density and frequency of D-layer, N=400 electron

c{c^{ - 1}},v = 200\,kHz

View answer and explanation

Correct option: C

6.9 \times {10^8}\mathrm{m}{\mathrm{s}^{ - 1}}

Option C (

6.9 \times {10^8}\mathrm{m}{\mathrm{s}^{ - 1}}

) is correct because it is the calculated phase velocity using the given electron density and frequency.

14 Medium

14 of 44

Understanding +4 | -1

Which of the following explain that all galaxies are receding from us?

View answer and explanation

Correct option: D

Red shift

Option D (Red shift) explains that all galaxies are receding from us because the observed light from these galaxies is shifted towards the red end of the spectrum, indicating they are moving away.

15 Medium

15 of 44

Analyzing +4 | -1

A ground receiver station is receiving a signal at

100 \mathrm{~MHz}

, transmitted from a ground transmitter at a height of

300 \mathrm{~m}

located at a distance of

100 \mathrm{~km}

. Then,

\left(N_{\max}=10^{12}\right.

per

\left.\mathrm{m}^3\right)

View answer and explanation

Correct option: C

Signal is coming via satellite transponder

Option C is correct because the frequency and distance suggest the signal is being relayed via a satellite transponder.

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16 Easy

16 of 44

Application +4 | -1

In AM modulation, a signal is modulated on a carrier wave such that maximum and minimum amplitudes are found to be

6 \mathrm{~V}

and

2 \mathrm{~V}

respectively. The modulation index is

View answer and explanation

Correct option: D

0.5

Option D (0.5) is correct because the modulation index is calculated as (Amax - Amin) / (Amax + Amin).

17 Easy

17 of 44

Application +4 | -1

Find the modulation index of an AM wave having 8

\mathrm{V}

variation where maximum amplitude of the AM wave is

9 \mathrm{~V}

View answer and explanation

Correct option: A

0.8

Option A (0.8) is correct because the modulation index is calculated as variation/ (2 * A_carrier), where A_carrier is A_max - variation/2.

18 Medium

18 of 44

Understanding +4 | -1

A transmitter transmits the message in original

View answer and explanation

Correct option: D

Never true

Option D (Never true) is correct because a transmitter modifies the original message signal for efficient transmission, it does not transmit the message in its original form.

19 Medium

19 of 44

Application +4 | -1

The resistance of copper wire of diameter=2 mm is of the order of

View answer and explanation

Correct option: A

0.1\mathrm{\;\Omega }{\mathrm{m}^{ - 1}}

Option A (

0.1\mathrm{\;\Omega }{\mathrm{m}^{ - 1}}

) is correct because it represents the typical resistance order of magnitude for a copper wire with the given diameter.

20 Easy

20 of 44

Remembering +4 | -1

In earth's atmosphere, for E-layer, the virtual height and critical frequency are

View answer and explanation

Correct option: D

110 km and 4 MHz

Option D, 110 km and 4 MHz, is the closest to the typical values for the E-layer virtual height and critical frequency in Earth's atmosphere.

21 Medium

21 of 44

Application +4 | -1

{E_c} = 20\sin {10^5}\;\pi t

and

{E_m} = 10\sin 400\;\pi t

are carrier and modulating signals respectively, The modulation index is 

View answer and explanation

Correct option: C

0.5

Option C (0.5) is correct because the modulation index is the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

22 Medium

22 of 44

Remembering +4 | -1

The galaxy in which we live is

View answer and explanation

Correct option: A

Milkyway

Option A, Milkyway, is correct because the galaxy containing our solar system is called the Milky Way.

23 Medium

23 of 44

Application +4 | -1

The modulation index of a FM signal is 0.25. If modulating frequency is 2kHz, the maximum derivative in frequency would be

View answer and explanation

Correct option: A

500 Hz

Option A (500 Hz) is correct because the maximum frequency deviation is the product of the modulation index and the modulating frequency.

24 Hard

24 of 44

Understanding +4 | -1

In a radio receiver, the short wave and medium wave stations are tuned by using the same capacitor but coils of different inductance

{L_s}

and

{L_m}

respectively then

View answer and explanation

Correct option: B

{L_s} < {L_m}

Option B (

{L_s} < {L_m}

) is correct because for the same capacitor, a lower inductance is required for tuning to higher frequencies (short waves) and a higher inductance is required for tuning to lower frequencies (medium waves).

25 Hard

25 of 44

Application +4 | -1

Two electrons are moving in opposite direction with speeds 0.8 c and 0.4 c, where c the speed of light in vacuum. Then the relative speed is about

View answer and explanation

Correct option: C

0.9 c

Option C (0.9 c) is correct because it represents the relative speed calculated using the relativistic velocity addition formula.

26 Medium

26 of 44

Remembering +4 | -1

The characteristic impedance

\left( {{\mathrm{Z}_0}} \right)

of free space is

View answer and explanation

Correct option: A

377 W

Option A, 377 W, is the correct characteristic impedance of free space, often approximated as 120π ohms.

27 Easy

27 of 44

Remembering +4 | -1

The sky wave propagation is suitable for radio-waves of frequency

View answer and explanation

Correct option: C

From 2 MHz to 30 MHz

Option C, From 2 MHz to 30 MHz, is correct because sky wave propagation, which relies on ionospheric reflection, is most effective within this frequency range.

28 Medium

28 of 44

Application +4 | -1

If the area to be covered for TV telecast is doubled, then height of transmitting antenna (TV tower) will have to be

View answer and explanation

Correct option: A

Doubled

Option A (Doubled) is correct because the area covered is proportional to the height of the transmitting antenna.

29 Easy

29 of 44

Application +4 | -1

The audio signal used to modulate

60\sin \left( {2\pi \times {{10}^6}\;t} \right)

15\,\,\sin \,\,300\pi t.

The depth of modulation is

View answer and explanation

Correct option: C

0.25

Option C (0.25) is correct because the depth of modulation is calculated as the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.

30 Medium

30 of 44

Analyzing +4 | -1

According to the station clocks, two babies are born at the same instant, one in Howrah and other in Delhi. (a) Who is elder in the frame of 2301 Up Rajdhani Express going from Howrah to Delhi? (b) Who is elder in the frame of 2302 Dn Rajdhani Express going from Delhi to Howrah.

View answer and explanation

Correct option: A

(a) Delhi baby is elder (b) Howrah baby is elder

Option A is correct because of the relative motion between the trains and the birth events, considering the concept of relativity of simultaneity.

Revision notes and key takeaways

Review COMMUNICATION SYSTEMS in your textbook or class notes, then use this set to check your understanding.

Key Takeaways

✓ This set contains 44 single-correct-answer MCQs on COMMUNICATION SYSTEMS.
✓ Try each question before opening its answer. Read the explanation where one is available.
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