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Physics NEET MCQ
Electromagnetic Wave And Communication Mcq
Quiz 10
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Q.1
A T.V. tower has a height 200 m. By how much the height of tower be increased totriple its coverage range ?
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a)1600 m
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b)800 m
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c)1800 m
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d)600 m
Explanation
Answer:(a)
Q.2
The transmission of audio signal in radio broadcasting is type.
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a) ASK
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b) FSK
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c) AM
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d) FM
Explanation
Answer: (c)
Q.3
Transmission loss per km in the optical fibre,used presently is,
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a)20 dB
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b) 2 dB
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c)0.2 dB
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d)0.02 dB
Explanation
Answer: (c)
Q.4
In satellite communication 6 GHz frequency is used for and 4 GHz frequencyis used for
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a)uplink, down link
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b)down link, up link
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c)modulation, demodulation
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d)demodulation, modulation
Explanation
Answer: (a)
Q.5
If a radio receiver amplifier all the signal frequencies equally well, it is said to have high
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a) fidelity
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b)distortion
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c)sensibility
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d) sensitivity
Explanation
Answer:(d)
Q.6
In frequency modulation
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a) the amplitude of modulated wave varies as frequency of carrier wave.
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b) the frequency of modulated wave varies as amplitude of modulating wave.
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c) The amplitude of modulated wave varies as amplitude of carrier wave.
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d) The frequency of modulated wave varies as frequency of modulating wave.
Explanation
Answer: (b)
Q.7
When electromagnetic waves enter the ionized layer of ionosphere, the relative permittingof the ionized layer
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a)remain constant
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b) appears to decrease
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c)appears to increase
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d)changes randomly
Explanation
Answer: (b)
Q.8
For 100% modulation, What is the value of minimum amplitude Emin of the modulatedwave ?
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a)Zero
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b)1
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c)2
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d)3
Explanation
Answer: (a)
Q.9
The velocity of e.m. waves in a medium is 2.5×108 m/s . what is the dielectric constantof the medium ?
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a)1.2
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b)1.44
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c)0.69
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d)1.6
Explanation
Answer:(a)
Q.10
The condition under which a microwave oven heats up a food item containing water molecules most efficiently is … [ NEET 2013]
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a) The frequency of the microwaves must match the resonant frequency of the water molecules
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b) The frequency of the microwaves has no relation with natural frequency of water molecules
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c) Microwaves are heat waves, so always produce heating
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d) Infra-red waves produce heating in a microwave oven
Explanation
Answer:(a)
Q.11
Light with an energy flux of 25 × 104Wm–2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm2, the average force exerted on the surface is … [AIPMT 2014]
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a) 1.20 × 10–6 N
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b) 3.0 × 10–6 N
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c) 1.25 × 10–6 N
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d) 2.50 × 10–6 N
Explanation
Given surface is perfectly reflecting surface Change in momentum or force Energy on 15cm2 = 25×104×15×10-4 = 375W Answer:(c)
Q.12
A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (C = Velocity of light) …[ NEET 2015]
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a) E/C2
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b) E/C
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c) 2E/C
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d) 2E/C2
Explanation
Given surface is perfectly reflecting surface Change in momentum or force Δp = 2ΔU/C = 2E/C Answer:(c)
Q.13
Out of the following options which one can be used to produce a propagating electromagnetic wave ?
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a) A charge moving at constant velocity
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b) A stationary charge
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c) A charge less particle
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d) An accelerating charge
Explanation
Answer:(d)
Q.14
In an electromagnetic wave in free space the root mean square value of the electric field is Erms= 6 V/m. The peak value of the magnetic field is
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a) 1.41 × 10–8 T
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b) 2.83 × 10–8 T
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c) 0.70 × 10–8 T
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d) 4.23 × 10–8 T
Explanation
Erms = Brms c 6=Brms × 3 ×108 Brms = 2×10-8 T Bpeak = Brms × √2 Bpeak = √2 × 2×10-8 = 2.83 × 10–8 T Answer:(b)
Q.15
A diode detector is used to detect an amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance 100 kilo ohm. Find the maximum modulated frequency which could be detected by it. … [ IIT main 2013]
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a) 10.62 MHz
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b) 10.62 kHz
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c) 5.31 MHz
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d) 5.31 kHz
Explanation
At resonance frequency circuit becomes purely resistive such that power ouput is maximum R = XC R=1/ωC The higher frequency which can be detected with tolerable distortion is F = 10.62 kHz Answer:(b)
Q.16
The magnetic field in a travelling electromagnetic wave has a peak value of 20 nT. The peak value of electric field strength is …[ IIT Mains 2013]
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a) 3 V/m
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b) 6 V/m
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c) 9 V/m
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d) 12 V/m
Explanation
E0 = B0C E0 = (20 × 10-9) × 3×108= 6 V/m Answer:(b)
Q.17
A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3 × 108 ms−The final momentum of the object is
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a) 0.3 × 10−17 kg ms−1
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b) 1.0 × 10−17 kg ms−1
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c) 3.0 × 10−17 kg ms−1
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d) 9.0 × 10−17 kg ms−1
Explanation
Total absorption of radiation Δp= 1.0 × 10−17 kg ms−1 Answer:(b)
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