# JEE Main > Communication System

Explore popular questions from Communication System for JEE Main. This collection covers Communication System previous year JEE Main questions hand picked by popular teachers.

Physics
Chemistry
Maths

Q 1.

Correct4

Incorrect-1

In short wave communication waves of which of the following frequencies will be reflected back by the ionospheric layer, having electron density 10 'per {tex} m {/tex}

{tex} 2 \,M H z {/tex}

B

10 {tex} M H z {/tex}

C

{tex} 12 \,{ MHz } {/tex}

D

{tex} 18 \,{ MHz } {/tex}

##### Explanation Q 2.

Correct4

Incorrect-1

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

A

50 cycles/sec

B

100 cycles/sec

C

500 cycles/sec

50,000 cycles/sec

##### Explanation Q 3.

Correct4

Incorrect-1

AM is used for broadcasting because

A

It is more noise immune than other modulation systems

B

It requires less transmitting power compared with other systems

D

No other modulation system can provide the necessary bandwidth faithful transmission

##### Explanation

Q 4.

Correct4

Incorrect-1

{tex} \mathrm {88 \,\,to\,\, 108 }\,\,\ MHz {/tex}

B

{tex} \mathrm {88 \,\,to\,\, 108 }\,\,\ KHz {/tex}

C

{tex} \mathrm {8 \,\,to\,\, 88 }\,\,\ MHz {/tex}

D

{tex} \mathrm {88 \,\,to\,\, 108 }\,\,\ GHz {/tex}

##### Explanation Q 5.

Correct4

Incorrect-1

The velocity factor of a transmission line {tex} x {/tex}. If dielectric constant of the medium is {tex} 2.6 , {/tex} the value of {tex} x {/tex} is

A

0.26

0.62

C

2.6

D

6.2

##### Explanation Q 6.

Correct4

Incorrect-1

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

A

Transmission

B

Reception

Modulation

D

Detection

##### Explanation Q 7.

Correct4

Incorrect-1

A

Ground wave

B

lonospheric wave

Direct wave

D

Sky wave

##### Explanation

Q 8.

Correct4

Incorrect-1

A step index fibre has a relative refractive index of {tex} 0.88 \% . {/tex} What is the critical angle at the corecladding interface

A

{tex} 60 ^ { \circ } {/tex}

B

{tex} 75 ^ { \circ } {/tex}

C

{tex} 45 ^ { \circ } {/tex}

None of these

##### Explanation Q 9.

Correct4

Incorrect-1

The characteristic impedance of a coaxial cable is of the order of

A

{tex} {50 \,\Omega} {/tex}

B

{tex} {200 \,\Omega} {/tex}

{tex} {270\, \Omega} {/tex}

D

None of these

##### Explanation

Q 10.

Correct4

Incorrect-1

In which frequency range, space waves are normally propagated

A

{tex} \mathrm { HF } {/tex}

B

{tex} \mathrm { VHF } {/tex}

{tex} \mathrm {UHF} {/tex}

D

{tex} \mathrm { SHF } {/tex}

##### Explanation

Q 11.

Correct4

Incorrect-1

If {tex} \mu {/tex} and {tex} \mu_{1}{/tex} are the refractive indices of the materials of core and cladding of an optical fibre, then the loss of light due to its leakage
can be minimised by having

{tex} \mu > \mu_{1} {/tex}

B

{tex} \mu < \mu_{1} {/tex}

C

{tex} \mu = \mu_{1} {/tex}

D

None of these

##### Explanation

Q 12.

Correct4

Incorrect-1

Through which mode of propagation, the radio waves can be sent
from one place to another

A

Ground wave propagation

B

Sky wave propagation

C

Space wave propagation

All of them

##### Explanation Q 13.

Correct4

Incorrect-1

A laser beam of pulse power 10 watt is focussed on an object are 10 cm. The energy flux in wattl {tex} c m {/tex} at the point of focus is

A

10{tex}^{20}{/tex}

10{tex}^{16}{/tex}

C

10{tex}^{8}{/tex}

D

10{tex}^{4}{/tex}

##### Explanation Q 14.

Correct4

Incorrect-1

The carrier frequency generated by a tank circuit containing 1 {tex} n F {/tex} capacitor and {tex} 10 \mu H {/tex} inductor is

A

{tex} 1592 \mathrm{ Hz } {/tex}

B

{tex} 1592 \mathrm { MHz } {/tex}

{tex} 1592 \mathrm { kHz } {/tex}

D

{tex} 159.2 \mathrm { Hz } {/tex}

##### Explanation Q 15.

Correct4

Incorrect-1

A

Omnidirectional type

Vertical type

C

Horizontal type

D

None of these

##### Explanation

Q 16.

Correct4

Incorrect-1

For television broadcasting, the frequency employed is normally

{tex} 30 - 300\, M H z {/tex}

B

{tex} 30 - 300\, G H z {/tex}

C

{tex} 30 - 300 \,K H z {/tex}

D

{tex} 30 - 300 \,H z {/tex}

##### Explanation Q 17.

Correct4

Incorrect-1

The radio waves of frequency {tex} 300 \mathrm{ MHz } {/tex} to {tex} 3000 \mathrm{ MHz } {/tex} belong to

A

High frequency band

B

Very high frequency band

Ultra high frequency band

D

Super high frequency band

##### Explanation

Q 18.

Correct4

Incorrect-1

An antenna behaves as resonant circuit only when its length is

A

{tex} \frac { \lambda } { 2 } {/tex}

B

{tex} \frac { \lambda } { 4 } {/tex}

C

{tex} \lambda {/tex}

{tex} \frac { \lambda } { 2 } {/tex} or integral multiple of {tex} \frac { \lambda } { 2 } {/tex}

##### Explanation

Q 19.

Correct4

Incorrect-1

Maximum useable frequency (MUF) in F region layer is {tex} x , {/tex} when the critical frequency is {tex} 60 \mathrm { MHz } {/tex} and the angle of incidence is {tex} 70 ^ { \circ } . {/tex} Then {tex} x {/tex} is

A

{tex} 150 \mathrm { MHz } {/tex}

B

{tex} 170 \mathrm{ MHz} {/tex}

{tex} 175 \mathrm { MHz } {/tex}

D

{tex} 190\mathrm { MHz } {/tex}

##### Explanation Q 20.

Correct4

Incorrect-1

The electromagnetic waves of frequency {tex} 2 \mathrm{ MHz } {/tex} to {tex} 30 \mathrm { MHz } {/tex} are

A

In ground wave propagation

In sky wave propagation

C

In microwave propagation

D

In Satellite communication

##### Explanation

Q 21.

Correct4

Incorrect-1

A laser is a coherent source because it contains

A

Many wavelengths

B

Uncoordinated wave of a particular wavelength

C

Coordinated wave of many wavelengths

Coordinated waves of a particular wavelength

##### Explanation

Q 22.

Correct4

Incorrect-1

The attenuation in optical fibre is mainly due to

A

Absorption

B

Scattering

C

Neither absorption nor scattering

Both (a) and (b)

##### Explanation Q 23.

Correct4

Incorrect-1

The maximum distance upto which TV transmission from a TV tower of height {tex} h {/tex} can be received is proportional to

h{tex}^{1/2}{/tex}

B

h{tex}^{2}{/tex}

C

h{tex}^{6}{/tex}

D

h{tex} {/tex}

##### Explanation Q 24.

Correct4

Incorrect-1

A laser beam is used for carrying out surgery because it

A

Is highly monochromatic

B

Is highly coherent

C

Is highly directional

Can be sharply focussed

##### Explanation Q 25.

Correct4

Incorrect-1

Laser beams are used to measure long distances because

A

They are monochromatic

B

They are highly polarised

C

They are coherent

They have high degree of parallelism

##### Explanation 