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Physics NEET MCQ
Electromagnetic Wave And Communication Mcq
Quiz 8
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Q.1
An electromagnetic wave going through vaccum is described by E=Eo sin(kx- ω t) then B=Bo sin(kx- ω t) then
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a) EoBo= ω k
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b) Eok = Bo ω
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c) Eo ω = Bok
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d) none of these
Explanation
Answer: (b)
Q.2
If the wavelength of light is 40000 A then the number of waves in 1mm length will be___
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a) 2.5
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b) 2500
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c) 250
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d) 25000
Explanation
Answer:(b)
Q.3
The SI unit of displacement current is_________
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a) coulomb
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b) henry
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c) ampere
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d) faraday
Explanation
Answer: (c)
Q.4
The electromagnetic waves do not transport_______
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a)energy
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b)charge
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c)momentum
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d)information
Explanation
Answer: (b)
Q.5
The frequency 1057MHz of radiation arising from two close energy levels inhydrogen belongs to_____
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a) radio waves
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b)infrared waves
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c)micro waves
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d)γ rays
Explanation
Answer: (a)
Q.6
Maxwell’s modified form of Ampere’s circuital law is____
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a)
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b)
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c)
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d)
Explanation
Answer:(c)
Q.7
The wavelength of x rays is of the order of
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a) 10–3 m
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b) 10–5 m
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c) 10–10 m
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d) 10–12 m
Explanation
Answer: (c)
Q.8
A point source of electromagnetic radiation has an average output power of 800W.The maximum value of electric field at a distance of 4.0m from the source is
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a)64.7V/m
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b)57.8V/m
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c)56.72V/m
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d)54.77V/m
Explanation
Intensity of radiation I = Power/Area ....(i) and Intenisty of ration I = ½ ε0cE2 ....(ii) From (i) and (ii) we get Answer: (d)
Q.9
A plane electromagnetic wave Ez=100cos(6 ×108t + 4x) V/m propagate in a medium of refractive index
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a) 1.5
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b) 2.0
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c)2.4
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d)4.0
Explanation
Answer: (b)
Q.10
A plane electromagnetic wave of wave intensity 10 wm-2 strikes a small mirror ofarea 20 cm2 , held perpendicular to the approaching wave. The radiation force onthe mirror will be
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a)6.6×10-11 N
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b)1.33×10-11 N
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c)1.33×10-10 N
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d)6.6×10-10 N
Explanation
Force Total reflection of radiation Force = 2ΔU/c ΔU = I ×A ΔU = 20 ×10×10-4 =0.02 Force = 2×0.02 / 3×10-8 F = 1.33 × 10-10N Answer:(c)
Q.11
An observer is at 2m from an isotropic point source of light emitting 40w power.The rm.s value of electric due to the source at the position of the observeris_____
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a) 5.77 × 10-8 V/m
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b) 17.3 V/m
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c) 57.7 × 10-8
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d) 1.73
Explanation
Answer: (b)
Q.12
The instrument/ equipment which transform one form of energy into another form of energy is called a _______
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a)transponder
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b) transducer
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c)receiver
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d)transmitter
Explanation
Answer: (b)
Q.13
Which of the following are modulation techniques for digital communication?
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a) ASK
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b) FSK
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c)PSK
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d)All of them
Explanation
Answer: (d)
Q.14
What is the main function of transponder
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a) To amplify the signal
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b) To change its frequency
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c)Both (a) and (b)
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d)none of them
Explanation
Answer:(b)
Q.15
Electromagnetic waves used in medicine to destroy cancer cells
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a) radio waves
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b) infrared rays
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c) gamma rays
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d) ultraviolet rays
Explanation
Answer: (c)
Q.16
In electromagnetic spectrum, the visible light lie between
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a)radiowaves and microwaves
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b) ultraviolet rays and infrared rays
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c)ultraviolet rays and x rays
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d)infrared rays and microwaves
Explanation
Answer: (b)
Q.17
Which of the following statements is not true in case of electromagnetic waves?
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a)they are light waves
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b)they are transverse waves
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c)propagates through space
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d)they are longitudinal waves
Explanation
Answer: (d)
Q.18
In an electromagnetic wave in free space, the direction of electric field vector E is along y axis and magnetic field vector B is along z axis then which of the following is true
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a)(E × B) × E=1
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b)(E × B) × B=1
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c)(E × B) × B=0
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d)none of these
Explanation
Answer:(a)
Q.19
When a plane electromagnetic wave travels in vacuum, the average electric energydensity is given by (Eo is the amplitude of the electric field)
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a)
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b)
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c)
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d)
Explanation
Answer: (a)
Q.20
In a plane electromagnetic wave , the electric field oscillates sinusoidaly at a frequency of 2.0×1010Hz. if the peak value of electric field is 60V/m the average energy density (in Jm-3) of the magnetic field of the wave will be
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a)2π×10-7
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b) 10-7 / 2π
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c)4π×10-7
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d) 10-7 / 4π
Explanation
Answer: (b)
Q.21
If the earth were not having atmosphere, its temperature________.
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a)would have been low
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b)would have been high
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c)would hav remain constant
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d)none of these
Explanation
Answer: (a)
Q.22
_________ is responsible for the green house effect
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a) infrared rays
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b) ultraviolet rays
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c)x raya
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d)radiowaves
Explanation
Answer:(a)
Q.23
When an electromagnetic wave encounters a dielectric medium, the transmittedwave has
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a) same frequency but different amplitude
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b) same amplitude but different frequency
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c) same frequency and amplitude
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d) different frequency and amplitude
Explanation
Answer: (a)
Q.24
An electromagnetic wave
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a)can be deflected by electric field
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b)can be deflected by magnetic field
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c)can be deflected bye both electric and magnetic field
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d)none of these
Explanation
Answer: (d)
Q.25
The potential difference between the plates of a parallel plate capacitor is chargingat the rate of 106V/s . If the capacitance is 2µF . The displacement current inthe dielectric of the capacitor will be
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a)4A
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b)3A
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c)2A
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d)1A
Explanation
Answer: (c)
Q.26
What should be the minimum length of the antenna capable of emitting audio signal ofwave length λ ?
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a)λ/4
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b) λ/8
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c)λ/2
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d)λ
Explanation
Answer:(a)
Q.27
_________is used as a medium an space communication
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a) Two wire line
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b) Space
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c) Amplifier
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d) Optical fibre
Explanation
Answer: (b)
Q.28
The band width of Audio signal is
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a)20 HZ
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b)20 KHZ
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c)20 MHz
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d)20 GHz
Explanation
Answer: (b)
Q.29
ground waves are polarized at direction.
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a)vertically upward
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b)horizontal
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c)tangential direction to the surface of the earth
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d)in all four.
Explanation
Answer: (a)
Q.30
Intensity of electric field of ground waves is in of the distance travelled by it.
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a) Square
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b) inverse of root
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c)proportion
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d)inverse
Explanation
Answer:(d)
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