The relation between the maximum electron density ${N_{{\rm{max}}}}$ and the critical frequency ${f_c}$ for the ionosphere can be given as

${f_c} = 9\sqrt {\;{N_{{\rm{max}}}}} $

${f_c} = \sqrt {9\;{N_{{\rm{max}}}}} $

${f_c} = \sqrt {9\;} {N_{{\rm{max}}}}$

Thinning of ozone layer in troposphere

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JEE • PHYSICS • COMMUNICATION SYSTEMS

Communication systems practice · Medium

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Practice format and chapter quiz

These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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Showing 1-30 of 113 questions

1 Medium

1 of 113

Understanding +4 | -1

Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line of sight communication? A TV transmitting antenna is

81 {~m}

tall. How much service area can it cover, if the receiving antenna is at the ground level?

View answer and explanation

Correct option: B

3260 {~km}^2

Option B is correct. The service area is calculated using the formula Area =

\pi d^2

where d is the range, and the range d =

\sqrt{{2hR}}

, resulting in approximately 3260 km².

2 Medium

2 of 113

Remembering +4 | -1

The radio waves of frequency 30 MHz to 300 MHz belong to

View answer and explanation

Correct option: B

Very high frequency band

Option B (Very high frequency band) is correct because radio waves with frequencies between 30 MHz and 300 MHz are classified as belonging to the VHF band.

3 Medium

3 of 113

Remembering +4 | -1

The wavelength of the carrier waves in a modern optical fibre communication network is close to

View answer and explanation

Correct option: B

1500 nm

The correct answer is B (1500 nm) because modern optical fiber communication networks operate in the range of 1310 nm - 1550 nm.

4 Medium

4 of 113

Understanding +4 | -1

In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be

View answer and explanation

Correct option: D

50,000 cycles/s

Option D (50,000 cycles/s) is correct because the carrier frequency must be significantly higher than the audio frequency in amplitude modulation.

5 Medium

5 of 113

Understanding +4 | -1

100 \%

modulation in FM means

View answer and explanation

Correct option: B

Actual frequency deviation

=

maximum allowed frequency deviation

Option B (Actual frequency deviation

=

maximum allowed frequency deviation) is correct because 100% modulation means the actual deviation reaches the maximum limit.

6 Medium

6 of 113

Remembering +4 | -1

The waves which can travel directly along surface of the earth are known as

View answer and explanation

Correct option: A

ground waves

Option A (ground waves) is correct because ground waves propagate along the surface of the Earth.

7 Medium

7 of 113

Understanding +4 | -1

Which of the following statements is wrong?

View answer and explanation

Correct option: C

Sky wave propagation is useful in the range of 30 to 40 MHz

Option C (Sky wave propagation is useful in the range of 30 to 40 MHz) is wrong because sky wave propagation typically occurs at lower frequencies.

8 Medium

8 of 113

Application +4 | -1

A sinusoidal wave

y\left( t \right) = 40\sin \left( {10 \times {{10}^6}\,\,\pi t} \right)

is amplitude modulated by another sinusoidal wave

x\left( t \right) = 20\sin \left( {1000\,\pi t} \right).

The amplitude of minimum frequency component of modulated signal is:

View answer and explanation

Correct option: D

Option D (10) is correct because it identifies the minimum frequency component of the modulated signal and its corresponding amplitude after expanding the expression.

9 Medium

9 of 113

Understanding +4 | -1

Which one of the following is correct?

View answer and explanation

Correct option: B

Atleast three geostationary satellites in the same orbit around earth's can cover the whole part of the earth for microwave communication

Option B is correct. At least three geostationary satellites are needed to provide complete global coverage for microwave communication.

10 Medium

10 of 113

Application +4 | -1

An antenna has a radiation resistance of 68

\Omega

, a load resistance of 10

\Omega

, and power gain of 16. The directive gain of the antenna is

View answer and explanation

Correct option: D

18.35

Option D (18.35) is correct because the directive gain is calculated by dividing the power gain by the antenna efficiency.

11 Medium

11 of 113

Understanding +4 | -1

Television signals on earth cannot be received at distances greater than

100 \mathrm{~km}

from the transmission station. The reason behind this is that

View answer and explanation

Correct option: D

The surface of earth is curved like a sphere

Option D (The surface of earth is curved like a sphere) is correct because TV signals are electromagnetic waves that travel in straight lines and cannot bend around the Earth's curvature.

12 Medium

12 of 113

Remembering +4 | -1

The fact that radio signal reach the earth from outside the atmosphere, was discovered accidently by

View answer and explanation

Correct option: A

K. G. Jansky

Option A (K. G. Jansky) is correct because Jansky accidentally discovered radio signals from outside the atmosphere.

13 Medium

13 of 113

Application +4 | -1

A 1000kHz carrier wave is modulated by audio signal of frequency range 100-5000Hz. Then the width of the channel in kHz is

View answer and explanation

Correct option: A

Option A (10) is correct because the channel width is twice the maximum frequency of the modulating signal.

14 Medium

14 of 113

Remembering +4 | -1

The characteristic impedance

\left( {{Z_0}} \right)

parallel line wire is

View answer and explanation

Correct option: A

{Z_0} = \frac{{276}}{{\sqrt k }}\log \frac{{2s}}{d}

Option A (

{Z_0} = \frac{{276}}{{\sqrt k }}\log \frac{{2s}}{d}

) is correct because it represents the characteristic impedance of a parallel line wire.

15 Medium

15 of 113

Understanding +4 | -1

Assertion : In a communication system based on amplitude modulation index is kept

Reason : It ensures minimum distortion of signal

View answer and explanation

Correct option: A

If both Assertion & reason are True & the reason is a correct explanation of the assertion

Option A (If both Assertion & reason are True & the reason is a correct explanation of the assertion) is correct because maintaining a modulation index less than or equal to 1 ensures minimal distortion of the signal in amplitude modulation.

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16 Medium

16 of 113

Remembering +4 | -1

Primary constant of a transmission line are

View answer and explanation

Correct option: C

Both (a) and (b)

Option C (Both (a) and (b)) is correct because the primary constants of a transmission line include both resistance and inductance, as well as capacitance and conductance.

17 Medium

17 of 113

Remembering +4 | -1

In earth's atmosphere, for

{F}_1

-layer; the virtual height and critical frequency are

View answer and explanation

Correct option: D

180 {~km}

and

5 {MHz}

Option D (

180 {~km}

and

5 {MHz}

) is correct because the F1 layer in the Earth's ionosphere typically has a virtual height around 180 km and a critical frequency around 5 MHz.

18 Medium

18 of 113

Application +4 | -1

Maximum usable frequency (MUF) in F-region layer is x, when the critical frequency is 60 MHz and the angle of incidence is 70°. Then x is

View answer and explanation

Correct option: C

175 MHz

Option D (190 MHz) is incorrect. Option C (175 MHz) is correct because the Maximum Usable Frequency (MUF) is calculated using the formula MUF = fc / cos(θ).

19 Medium

19 of 113

Understanding +4 | -1

Which of the following statements is/are correct?

View answer and explanation

Correct option: A

The space waves are the radio waves of frequency between

30 \,{MHz}

300 \,{MHz}

Option A (The space waves are the radio waves of frequency between

30 \,{MHz}

300 \,{MHz}

) is correct because space waves typically operate in the VHF and UHF bands, which fall within this frequency range.

20 Medium

20 of 113

Remembering +4 | -1

The waves related to tele-communication are

View answer and explanation

Correct option: C

Microwaves

Option C (Microwaves) is correct because microwaves are commonly used in telecommunications for transmitting signals over long distances, including satellite communication.

21 Medium

21 of 113

Remembering +4 | -1

Basically, the product modulator is

View answer and explanation

Correct option: B

A mixer

Option B (A mixer) is correct because a product modulator is essentially a mixer, combining two signals to produce sum and difference frequencies.

22 Medium

22 of 113

Understanding +4 | -1

Digital signals

(i) Do not provide a continuous set of values

(ii) Represent values as discrete steps

(iii) Can utilise binary system and

(iv) Can utilise decimal as well as binary systems

Which of the above statements are true?

View answer and explanation

Correct option: C

(i), (ii) and (iii)

Option C is correct. Digital signals do not provide continuous values, represent values as discrete steps, and can utilize the binary system.

23 Medium

23 of 113

Analyzing +4 | -1

Assertion (A) Audio signal of frequency

10\, {kHz}

cannot be transmitted over long distance without modulation.

Reason (R) Length of the antenna required

\lambda / 4

, should have practical value.

View answer and explanation

Correct option: A

If both Assertion and Reason are true and Reason is correct explanation of Assertion

Option A is correct because both Assertion and Reason are true, and Reason is the correct explanation of Assertion. Audio signals need modulation for long-distance transmission due to antenna length requirements.

24 Medium

24 of 113

Remembering +4 | -1

In amplitude modulation, carrier wave frequencies are

View answer and explanation

Correct option: A

Lower compared to those in frequency modulation

Option A (Lower compared to those in frequency modulation) is correct because AM carrier frequencies are generally in the range of 0.5-20 MHz, while FM carrier frequencies are 88-108 MHz.

25 Medium

25 of 113

Application +4 | -1

A message signal of frequency 100 MHz and peak voltage 100 V is used to execute amplitude modulation on a carrier wave of frequency 300 GHz and peak voltage 400 V. The modulation index and difference between the two side band frequencies are

View answer and explanation

Correct option: C

0.25\,\,;\,\,\,\,2 \times {10^8}\;Hz

Option C (

0.25\,\,;\,\,\,\,2 \times {10^8}\,Hz

) is correct because the modulation index is the ratio of message amplitude to carrier amplitude, and the bandwidth is twice the message frequency.

26 Medium

26 of 113

Remembering +4 | -1

Intelsat satellite is used for

View answer and explanation

Correct option: C

Intercontinental communication

Option C (Intercontinental communication) is correct because Intelsat satellites are specifically designed for long-distance, intercontinental communication.

27 Medium

27 of 113

Application +4 | -1

A TV tower has a height of

100 \mathrm{~m}

. The average population density around the tower is 1000 per

\mathrm{km}^2

. The radius of the earth is

6.4 \times 10^6 \mathrm{~m}

. The population covered by the tower is

View answer and explanation

Correct option: C

4 \times 10^6

Option C (

4 \times 10^6

) is correct because it is the calculated population covered by the TV tower based on its height and the population density around it.

28 Medium

28 of 113

Remembering +4 | -1

The relation between the maximum electron density

{N_{\mathrm{max}}}

and the critical frequency

{f_c}

for the ionosphere can be given as

View answer and explanation

Correct option: C

{f_c} = 9\sqrt {\;{N_{\mathrm{max}}}}

Option C (

{f_c} = 9\sqrt {\;{N_{\mathrm{max}}}}

) is correct because it represents the relationship between critical frequency and maximum electron density in the ionosphere.

29 Medium

29 of 113

Application +4 | -1

The amplitude of

15 \sin (1000 \pi t)

is modulated by

10 \sin (4 \pi \mathrm{t})

signal. The amplitude modulated signal contains frequency(ies) of
A.

500 \mathrm{Hz}

2 \mathrm{Hz}

250 \mathrm{Hz}

498 \mathrm{Hz}

502 \mathrm{Hz}

Choose the correct answer from the options given below

View answer and explanation

Correct option: C

A, D and E only

Option C (A, D and E only) is correct because amplitude modulation produces the carrier frequency and sideband frequencies (carrier frequency plus and minus the modulation frequency).

30 Medium

30 of 113

Understanding +4 | -1

What is ozone hole

View answer and explanation

Correct option: D

Reduction in ozone thickness in stratosphere

Reduction in ozone thickness in stratosphere is correct because the ozone hole refers to the thinning of the ozone layer in the stratosphere.

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 113 single-correct-answer MCQs on COMMUNICATION SYSTEMS.
✓ Try each question before opening its answer. Read the explanation where one is available.
✓ Sign in to save submitted answers. Revisit incorrect answers alongside your textbook or class notes.

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