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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 91-113 of 113 questions

91 Medium

91 of 113

Remembering +4 | -1

In earth's atmosphere, for

{\mathrm{F}_2}

-layer, the virtual height and critical frequency in night time are

View answer and explanation

Correct option: D

350 km and 6 MHz

Option D (350 km and 6 MHz) is correct because the virtual height of the F2 layer is typically around 350 km and the critical frequency is around 6 MHz during nighttime.

92 Medium

92 of 113

Remembering +4 | -1

The waves relevant to telecommunications are

View answer and explanation

Correct option: D

Microwave

Option D (Microwave) is correct because microwaves are commonly used in telecommunications due to their ability to penetrate the atmosphere and carry large amounts of information.

93 Medium

93 of 113

Application +4 | -1

A transmitting antenna of height h and the receiving antenna of height 45 m are separated by a distance of 40 km for satisfactory communication in line of sight mode. Then the value of h is

View answer and explanation

Correct option: B

20m

Option B (20m) is correct because it is the height calculated using the formula for the maximum distance for line of sight communication.

94 Medium

94 of 113

Understanding +4 | -1

Identify the incorrect statement from the following

View answer and explanation

Correct option: C

Modulation index μ is kept ≥1, to avoid distortion

Option C is correct because the modulation index must be less than or equal to 1 to avoid overmodulation and distortion of the signal.

95 Medium

95 of 113

Application +4 | -1

An oscillator is producing FM waves of frequency 2 kHz with a variation of 10 kHz. What is the modulating index?

View answer and explanation

Correct option: B

Option B (5) is correct because the modulation index is the ratio of frequency deviation to modulating frequency.

96 Medium

96 of 113

Understanding +4 | -1

A radio station has two channels. One is AM at 1020 kHz and the other FM at 89.5 Mhz. For good results you will use

View answer and explanation

Correct option: A

Longer antenna for the AM channel and shorter for the FM

Option A is correct because the antenna length is related to the wavelength of the signal, and AM has a longer wavelength than FM.

97 Medium

97 of 113

Remembering +4 | -1

A laser device produces amplification in the

View answer and explanation

Correct option: B

Ultraviolet or visible region

Option B (Ultraviolet or visible region) is correct because lasers operate in the ultraviolet, visible, or infrared regions of the electromagnetic spectrum.

98 Medium

98 of 113

Application +4 | -1

A TV transmission tower has a height of 140 m and the height of the receiving antenna is 40 m. What is the maximum distance upto which signals can be broadcasted from this tower in LOS (Line of Sight) mode? (Take, radius of earth

= 6.4 \times {10^6}m)

View answer and explanation

Correct option: A

65 km

Option A (65 km) is correct because it is calculated by summing the distances from both the transmitting and receiving antennas using the given formula.

99 Medium

99 of 113

Understanding +4 | -1

In satellite communication, the communication satellite;

View answer and explanation

Correct option: C

Receives the coming modulated microwave signal, amplifies it and returns it to earth at a different frequency

Option C (Receives the coming modulated microwave signal, amplifies it and returns it to earth at a different frequency) is correct because communication satellites act as repeaters, amplifying and retransmitting signals at different frequencies.

100 Medium

100 of 113

Understanding +4 | -1

zone layer above earth's atmosphere will not

View answer and explanation

Correct option: D

Reflect back radio waves

Option D (Reflect back radio waves) is correct because the ozone layer primarily absorbs UV radiation and does not significantly reflect radio waves, which are reflected by the ionosphere.

101 Medium

101 of 113

Remembering +4 | -1

The number of telephonic message which are carried by a fiber at an instant with much less intensity loss are

View answer and explanation

Correct option: C

2000

Option C (2000) is correct because optical fibers can carry approximately 2000 telephonic messages at an instant with minimal intensity loss.

102 Medium

102 of 113

Remembering +4 | -1

Which of the following frequencies does not belong to FM broadcast.

View answer and explanation

Correct option: B

64 MHz

Option B (64 MHz) is correct because the FM broadcast frequency range is typically between 88 MHz and 108 MHz.

103 Medium

103 of 113

Remembering +4 | -1

The fundamental radio antenna is a metal rod which has a length equal to

View answer and explanation

Correct option: C

\lambda / 4

in free space at the frequency of operation

Option C (

\lambda / 4

in free space at the frequency of operation) is correct because a quarter-wave antenna is a fundamental and commonly used antenna design.

104 Medium

104 of 113

Understanding +4 | -1

A laser is a coherent source it contains

View answer and explanation

Correct option: D

Coordinated waves of particular wavelength

Option D (Coordinated waves of particular wavelength) is correct because a laser emits coherent light, which consists of coordinated waves of a single wavelength.

105 Medium

105 of 113

Remembering +4 | -1

Advantage of optical fibre is

View answer and explanation

Correct option: D

High band width, high data transmission capacity and no EM interference

Option D (High band width, high data transmission capacity and no EM interference) is correct because optical fibers offer high bandwidth, high data transmission capacity, and immunity to electromagnetic interference.

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106 Medium

106 of 113

Application +4 | -1

A given fiber has core refractive index of 1.5 and a core cladding index difference factor (∆) of 0.01125. The numerical aperture is

View answer and explanation

Correct option: B

0.225

Option B (0.225) is correct because it is the result of applying the numerical aperture formula with the given refractive index and index difference factor.

107 Medium

107 of 113

Understanding +4 | -1

The closed structure of co-axial cable prevents inner copper wire or core or from radiating signal power. The statement is

View answer and explanation

Correct option: A

TRUE

Option A (TRUE) is correct because the closed structure of a coaxial cable effectively shields the inner conductor, preventing signal power radiation.

108 Medium

108 of 113

Application +4 | -1

A diode AM detector with the output circuit consisting of

R = 1\;\mathrm{kW}

and

C = 1\;\mathrm{\mu F}

would be more suitable for detecting a carrier signal of

View answer and explanation

Correct option: D

10 kHz

Option D (

\frac{1}{3} \pi q f l^2

) is correct because the magnetic moment is calculated by integrating the current due to each infinitesimal charge element along the rod.

109 Medium

109 of 113

Understanding +4 | -1

The power radiated from a linear antenna of length

l

is proportional to

(Given,

\lambda=

Wavelength of wave):

View answer and explanation

Correct option: B

\left(\frac{l}{\lambda}\right)^{2}

Option B (

(\frac{l}{\lambda})^{2}

) is correct because the power radiated from a linear antenna is proportional to the square of the ratio of the antenna's length to the wavelength.

110 Medium

110 of 113

Application +4 | -1

In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is

View answer and explanation

Correct option: D

1 million

Option D (1 million) is correct because the number of channels is the total available bandwidth divided by the bandwidth per channel.

111 Medium

111 of 113

Application +4 | -1

To double the covering range of a TV transmission tower, its height should be multiplied by

View answer and explanation

Correct option: B

Option B (4) is correct because the range of a TV transmission tower is proportional to the square root of its height, so to double the range, the height must be multiplied by 4.

112 Medium

112 of 113

Understanding +4 | -1

Venus looks brighter than other stars, due to

View answer and explanation

Correct option: B

It is closer to the earth than other stars

Option B (It is closer to the earth than other stars) is correct because proximity significantly affects apparent brightness.

113 Medium

113 of 113

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 is correct. Redshift is the phenomenon where the light from distant galaxies is shifted towards the red end of the spectrum, indicating that they are moving away from us.

Revision notes and key takeaways

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

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