JEE Questions for Physics Communication System Quiz 2

The special theory of relativity is based on the frame of reference which has constant...?

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Acceleration
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Speed
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Time interval
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Space interval

For sky wave propagation of 10 MHz signal, what should be the minimum electron density in ionosphere?

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~ 1.2 × 1012 m-3
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~ 106 m-3
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~ 2.3 × 104 m-3
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~ 1022 m-3

Which of the following four alternatives is not correct?
We need modulation

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to increase the selectivity
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to reduce the time lag between transmission and reception of the information signal
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to reduce the size of antenna
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to reduce the fractional bandwidth, that is the ratio of the signal bandwidth to the centre frequency

1000 kHz carrier wave is amplitude modulated by the signal frequency 200 Hz -4000 Hz. The channel width of this case is

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8 kHz
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4 kHz
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7.6 kHz
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3.8 kHz
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400 kHz

Assertion (A) Modem is a demodulator.
Reason (R) It works in both transmitting and receiving mode.

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Both A and R are correct and R is the correct explanation of A
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Both A and R are correct but R is not the correct explanation of A
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A is correct but R is incorrect
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A is incorrect but R is correct

A signal wave of frequency 12 kHz is modulated with a carrier wave of frequency 2.51 MHz. The upper and lower side band frequencies are respectively

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2512 kHz and 2508 kHz
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2522 kHz and 2488 kHz
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2502 kHz and 2498 kHz
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2522 kHz and 2498 kHz
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2512 kHz and 2488 kHz

The range of frequencies allotted for FM radio is

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88 to 108 kHz
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88 to 108 MHz
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47 to 230 kHz
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47 to 230 MHz
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470 to 960 MHz

A TV transmitting antenna is 128 m tall. If the receiving antenna is at the ground level, the maximum distance between them for satisfactory communication in line of sight mode is (radius of the earth = 6.4 × 10⁶ km)

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0%
2)
0%
0%

A radar has a power of 1 kW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (radius of the earth = 6.4 × 10⁶ m) is

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80 km
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16 km
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40 km
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64 km

A TV tower has a height 150 m. What is the total population covered by the TV tower, if the population density around the TV tower is 10³ km^-2 ? Radius of the earth is 6.4 × 10⁶m.

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60.288 lakh
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40.192 lakh
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100 lakh
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20.228 lakh

If μ₁ and μ₂ 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

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μ1 > μ2
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μ1 < μ2
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μ1 = μ2
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None of these

The relation between the maximum electron density N_max and the critical frequency f_c for the ionosphere can be given as

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0%
2)
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0%
None of the above

The attenuation in optical fibre is mainly due to

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absorption
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scattering
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Neither absorption nor scattering
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Both (and (2)

A diode AM detector with the output circuit consisting of R = 1kΩ and C = 1μF would be more suitable for detecting a carrier signal of

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0.1 kHz
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0.5 kHz
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1 kHz
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0.75 kHz
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10 kHz

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

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2 million
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10 million
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0.1 million
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1 million
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0.5 million

Optical fibre works on the principle of

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interference of light
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total internal reflection of light
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reflection of light
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diffraction of light

In satellite communication,
I. the frequency used lies between 5 MHz and 10 MHz
II. the uplink and downlink frequencies are different.
III. the orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°.
In the above statements,

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II and III are correct
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all are correct
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only II is correct
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I and II are correct
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only I is correct

The sky wave propagation is suitable for radio waves of frequency

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upto 2 MHz
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from 2 MHz to 20 MHz
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between 2 MHz to 30 MHz
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from 2 MHz to 50 MHz

The output stage of a television transmitter is most likely to be a

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plate–modulated class C amplifier
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grid–modulated class C amplifier
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screen–modulated class C amplifier
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grid–modulated class A amplifier

Consider telecommunication through optical fibres. Which of the following statements is not correct?

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Optical fibres can be of graded refractive index
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Optical fibres are subjected to electromagnetic interference from outside
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Optical fibres have extremely low transmission loss
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Optical fibres may have homogeneous core with a suitable cladding

The optical fibres have an inner core of refractive index n₁ and a cladding of refractive index n₂ , such that

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n1 ≤ n2
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n1 = n2
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n1 < n2
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n1 > n2
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n1 ≥ n2

Which frequency range is used for optical communication?

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100000 GHz to 400000 GHz
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200 kHz to 3 MHz
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30000 GHz to 6000 GHz
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None of the above

In coaxial cable the material used as space is

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teflon (or) polyethylene
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glass or mica
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a gaseous medium
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glass
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mica

The waves relevant to telecommunication are

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visible light
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infrared
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ultraviolet
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microwave
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None of the above

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

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doubled
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halved
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quadrupled
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kept unchanged

A broken ligament is being welded back in place using 20 ms pulses from a 0.5 W laser operating at a wavelength of 632 nm. The number of photons in 5 pulses of laser are

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1.59 × 10-18
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3.18 × 10-17
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1.59 × 1023
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3.18 × 1016

A laser beam of pulse power 10¹² W is focused on an object of area 10^-4cm². The energy flux in Watt cm^-2. The energy flux in Watt cm^-2 at the point of focus is