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Physics NEET MCQ
Electromagnetic Wave And Communication Mcq
Quiz 4
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Q.1
If E and B are the electric and magnetic field vectors of e.m. waves then the direction of propogation of e.m waves is along the direction of
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a) E
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b) B
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c) E × B
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d) none of these
Explanation
Answer: (c)
Q.2
In a plane e.m wave, the electric field oscillattes sinusoidally at frequency of 2 × 1010 Hz and amplitude 48 V/m. The wavelength of the wave is
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a)24 × 10-1 m
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b) 1.5 × 10-2 m
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c)4.16 × 108 m
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d)3 ×10-8 m
Explanation
Answer: (b)
Q.3
In the above question the amplitude of the oscillating magnetic field is
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a) 48 T
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b) 14.4 × 1010 T
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c)24 × 10-10 T
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d)1.6 × 10-7 T
Explanation
Answer: (d)
Q.4
A plane electromagnetic wave is incident on a meterial surfcae. If the wave delivers momentum ρ and energy E, then
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a) ρ=0, E=0
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b) ρ ≠ 0, E ≠ 0
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c)ρ ≠ 0, E=0
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d)ρ=0, E ≠ 0
Explanation
Answer:(b)
Q.5
If the earth did not have atmosphere, its surface temperature on a day time would be
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a) higher
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b) lower
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c) same as now
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d) not sure
Explanation
Answer: (a)
Q.6
The AM range of radio waves have frequency
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a)less than 30 MHz
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b) more than 30 MHz
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c)less than 20,000 Hz
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d)more than 20,000 Hz
Explanation
Answer: (a)
Q.7
Height 'h' of transmitting antenna when R is the radius of earth to have range 'd' is
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a) d2 / 2R
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b)√(2dR)
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c)2d2/R
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d)2R2 / d
Explanation
Answer: (a)
Q.8
A TV tower has a height of 100 m. How much population is covered by the TV broadcasrt if the average population density around the tower is 1000 km-2 ( radius of earth=6.37 × 106 m)
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a) 4 lakh
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b) 4 billion
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c)40,000
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d)40 lakh
Explanation
Answer:(d)
Q.9
Which of the following is better carrier of signals?
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a) radiowaves
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b) light waves
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c) micro waves
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d) ultrasonic waves
Explanation
Answer: (c)
Q.10
The minimum frequecny ν of continuous X-ray is related to the applied potential difference V as
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a)ν ∝ V
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b) ν ∝ V1/2
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c)ν ∝ V-3
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d)ν ∝ V4
Explanation
Answer: (a)
Q.11
Conduction current is
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a) continuous through out
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b) discontinuous in circuit with capacitors
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c)continuous wherever electric field chages
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d)continuous in every type of circuit
Explanation
Answer: (b)
Q.12
Ampere's circutl law holds good for
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a) conduction current
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b) dispalcement current
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c)both
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d)none of these
Explanation
Answer:(a)
Q.13
The energy of X-ray photon is 2200 eV. Its frequency would be
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a) 5.3 × 1016 Hz
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b) 5.3 × 1017 Hz
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c) 5.3 × 1018 Hz
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d) 5.3 × 1015 Hz
Explanation
Answer: (b)
Q.14
The amplitudes of electric and magnetic field related to each other are
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a)Eo=Bo
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b) Eo=cBo
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c)Eo=Bo/c
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d)Eo=c/Bo
Explanation
Answer: (b)
Q.15
At which of the following frequency / frequencies the communication will not be reliable for a receiver situated below horizon
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a) 100 kHz
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b) 1 MHz
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c)1 Ghz
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d)100 GHz
Explanation
Answer: (b.c)
Q.16
In short wave communication waves of which of the following frequencies will be rfeclected back by the ionosphereic layer, having electron density 1011 per m3?
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a) 2 Mhz
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b) 10 MHz
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c)12 MHz
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d)18 MHz
Explanation
Answer:(a)
Q.17
If µ1 and µ2 are the refractive indexes 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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a) µ1 > µ2
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b) µ1 < µ2
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c) µ1=µ2
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d) none of the above
Explanation
Answer: (a)
Q.18
A laser beam is used for carrying out surgery beacuse it
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a)is highly monocharomatic
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b) is higly coherent
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c)is higly directional
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d)can be spherply focussed
Explanation
Answer: (d)
Q.19
The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to
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a)√h
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b) h
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c)h3/2
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d)h2
Explanation
Answer: (a)
Q.20
The attenuation in optical fibre is maily due to
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a) absorption
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b) scattering
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c)neither absorption nor scattering
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d)both (a) and (b)
Explanation
Answer: (d)
Q.21
Modulation is used to
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a) reduce the bandwidth used
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b) separate the transmissions of different users
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c)ensure that intelligence may be transmitted to long distance
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d)allow the use of practical antinnas
Explanation
Answer:(a)
Q.22
The process of super imposing signal frequency ( i.e. audio wave) on the carrier wave is known as
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a) transmission
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b) reception
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c) modulation
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d) detection
Explanation
Answer: (c)
Q.23
AM is used for broadcasting because
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a)it is more noise immune than other modulation systems
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b) it requires less transmitting power compared with other systems
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c)its use avoids receiver complexity
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d)no other modulation system can provide the necessary bandwidth
Explanation
Answer: (c)
Q.24
The impedance of a perfect conductor to e.m. waves is
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a) zero
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b) 1
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c)∞
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d)none of these
Explanation
Answer: (a)
Q.25
The area to be covered for TV telecast is doubled. Then the height of transmitting antenna ( TV tower) will have to be
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a) douled
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b) halved
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c)quadrupled
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d)kept uncharged
Explanation
Answer:(a)
Q.26
Crystal oscillator is preferred for the generation of carrier waves because of
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a) large output power
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b) larger amplification
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c) larger voltage gain
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d) better stability
Explanation
Answer: (d)
Q.27
What is the minimum number of geostationary satellites required for un interrupted global coverage?
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a)3
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b) 5
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c)7
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d)9
Explanation
Answer: (a)
Q.28
Frequencies in the UHF range normally propogated by means of
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a) ground waves
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b) sky waves
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c)surface waves
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d)space waves
Explanation
Answer: (d)
Q.29
In AM systems, complete information is conveyed by transmitting in
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a) carrier
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b) lower side band
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c)upper side band
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d)any of the two side bands
Explanation
Answer:(d)
Q.30
In an amplitude modulated wave for audio frequency of 500 cycles/second. the appropriate carrier frequency will be
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a) 50 cycles/s
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b) 1000 cycles/s
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c) 500 cyles/s
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d) 50000 cycles/s
Explanation
Answer: (d)
0 h : 0 m : 1 s
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