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Electromagnetic Wave And Communication Mcq
Quiz 7
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Q.1
An electromagnetic wave going through vaccum is described by E=o E sin(kx- ω t).Which of the following is independent of the wavelength?
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a) ω
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b)k/ ω
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c) k ω
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d)k
Explanation
Answer: (c)
Q.2
Which of the following have zero average value in a plane electromagnetic wave?
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a) Electric energy
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b) Magnetic energy
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c) Electric field
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d)None of these.
Explanation
Answer:(c)
Q.3
If the relative permeability and dielectric constant of a given medium are equal to µr and K respectively, then the refractive index of the medium is equalto__________
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a) √(µr) K
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b) √(µr) Eo
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c) √(µo) Eo
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d) √(µr)/ K
Explanation
Answer: (a)
Q.4
Astraonomers have found that electromagnetic waves of wavelength 21cm arecontinuously reaching the Earth’s surface . Calculate the frequency of this radiation.(c=3 ×108m/s)
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a)14.28 GHz
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b)1.428 kHz
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c)1.428 MHz
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d)1.428 GHz
Explanation
Answer: (c)
Q.5
Electric field in an electromagnetic wave is given by E=50 sinω(t-x/c) NC-1 .Intensity of this wave is ___________ Wm-2
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a) 50
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b)1.1×108
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c)3.3
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d)5.5×10-19
Explanation
Answer: (c)
Q.6
The amplitude of the electric field in a parallel beam of light of intensity 2.0Wm-2is _______
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a) 38.8NC-1
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b) 19.4NC-1
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c)9.7NC-1
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d)None of these.
Explanation
Answer:(a)
Q.7
Speed of electromagnetic wave is the same
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a) for all wavelengths
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b) in all media
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c) for all intensities
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d) for all frequencies
Explanation
Answer: (c)
Q.8
The maximum electric field in a plane electromagnetic wave is 900NC-1 . The waveis going in the x direction and the electric field is in the y direction. The maximummagnetic field in the wave is ____________T
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a)3×10-8
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b) 3×10-6
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c)27×10-6
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d)27×1010
Explanation
Answer: (b)
Q.9
Electromagnetic waves are produced by
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a)a static charge
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b)a moving charge
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c)an accelerating charge
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d)chargeless particles
Explanation
Answer: (c)
Q.10
Maxwells equations are derived from the laws of___________
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a)electricity
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b) magnetism
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c)both electricity and magnetism
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d)mechanics
Explanation
Answer:(c)
Q.11
Which of the following electromagnetic waves has the longest wavelength?
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a) Radio waves
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b) Infrared radiations
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c) x rays
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d) visible rays
Explanation
Answer: (a)
Q.12
Which of the following electromagnetic waves has the highest frequency?
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a)radio waves
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b)micro waves
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c) γ rays
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d)x rays
Explanation
Answer: (c)
Q.13
The maximum value of E in an electromagnetic waves in air is equal to 6.0×10-4 Vm . The maximum value of B is ____________
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a) 1.8×105 T
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b) 2×104 T
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c)2×10-12 T
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d)1.8×1013 T
Explanation
Answer: (c)
Q.14
Dimensional formula of intensity of radiation is _____________
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a) M1L2T-2
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b) M1L0T-2
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c)M1L1T-3
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d)M1L0T-3
Explanation
Answer:(d)
Q.15
The frequency of an electromagnetic wave in free space is 3MHz. When it passesthrough a medium of relative permeability εr=4.0 , then its frequency
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a) becomes half
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b) become doubled
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c) remain same
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d) become √2 times
Explanation
Answer: (c)
Q.16
The frequency of electromagnetic wave having wavelength 25mm is _________ Hz
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a)1.2 ×1010
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b) 7.5 ×105
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c)1.2 ×108
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d)7.5 ×106
Explanation
Answer: (a)
Q.17
Unit of energy density of electromagnetic wave is _________
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a)Jm-3
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b)Jm-2
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c)wm-2
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d)None of these
Explanation
Answer: (a)
Q.18
What is the ratio of velocities of light rays of wavelengths 40000 Å and 80000 Å in vaccum ?
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a)1:2
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b) 1:1
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c)2:1
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d)cannot be determined
Explanation
Answer:(b)
Q.19
Which of the following rays are not electromagnetic waves?
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a) α rays
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b) β rays
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c) γ rays
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d) heat rays
Explanation
Answer: (b)
Q.20
A plane electromagnetic wave of frequency 25MHz travels in free space along thex direction. At a particular point in space and time E=6.3jVm-1 then Bat this point is__________
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a)2.1 × 10-8 i T
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b)2.1 × 10-8 k T
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c)1.89× 109 k T
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d)2.52× 10-7 k T
Explanation
Answer:(b)
Q.21
The magnetic field in a plane electromagnetic wave is given By=2×10-7 sin ( 0.5×103x + 1.5×1011t) T
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a) Ex=60 sin ( 0.5×103x + 1.5×1011t) V/m
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b) Ez=60 sin ( 0.5×103x + 1.5×1011t) V/m
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c) Ex=60 sin ( 1.5×103x + 0.5×1011t) V/m
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d) Ex=60×1015 sin ( 1.5×103x + 0.5×1011t) V/m
Explanation
Answer: (b)
Q.22
Light with an energy flux of w/m3 falls on a non-reflecting surface atnormal to surface. If the surface has an area of 20m2 . The average force exertedon the surface during 30 minutes is________
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a)6.48×105 N
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b)3.60×102 N
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c)1.2×10-6 N
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d)2.16×10-3N
Explanation
Answer: (b)
Q.23
Energy density of an electromagnetic wave of intensity 0.02 Wm-2 is _______
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a) 6.67×10-11 Jm-3
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b)6×106 Jm-3
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c)1.5×1010 Jm-3
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d)none of the above
Explanation
Answer: (a)
Q.24
The waves used in communication are generally called
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a)γ ray
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b) α ray
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c) microwaves
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d)radiowave
Explanation
Answer:(d)
Q.25
For an electromagnetic wave, the phase difference between vectors E and B (faraway from the source)
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a) 0
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b) π /2
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c) π
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d) 3π/2
Explanation
Answer: (a)
Q.26
The electric and magnetic field of an electromagnetic wave are
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a) in phase and perpendicular to each other
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b)in phase and parallel to each other
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c) in opposite phase and perpendicular to each other
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d) in opposite phase and parallel to each other
Explanation
Answer: (a)
Q.27
Unit of µo C is same as that of
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a)current
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b)resistance
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c) electric charge
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d) velocity
Explanation
Answer: (b)
Q.28
If the direction of magnetic field B at some instant is along +ve Z direction and the electromagnetic wave is propagating along +ve X direction, then the direction of electric field E at that instant is_________
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a) along -ve Y direction
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b) along +ve Y direction
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c) along +ve X direction
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d) along -ve X direction
Explanation
Answer: (b)
Q.29
The velocity of light in vaccum can be changed by changing____
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a) frequency
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b)wavelength
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c) amplitude
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d) none of these
Explanation
Answer: (d)
Q.30
Which of the Following is not a component of communication System ?
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a) Transmitter
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b) Transmission channel
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c) Noise
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d) Receiver
Explanation
Answer: (c)
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