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Electromagnetic Wave And Communication Mcq
Quiz 2
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Q.1
green-house effect is the heating up of earth's atmosphere due to ... [ CBSE-PMT 2002]
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a) green plants
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b) infra-red rays
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c)X-rays
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d)β-rays
Explanation
Infra red ray is the cause of Green House effect. the glass transmits visible light and short infra red rays which are absorbed by plants. Infra red rays which are absorbed by plants. Then it emits long infra red rays, which are reflected back by glass.Answer: (b)
Q.2
Pick out the longest wavelength from the following types of radiation... [ CBSE-PMT 1990]
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a) blue light
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b) gamma rays
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c)X-rays
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d)red light
Explanation
Answer:(d)
Q.3
It is necessary to use satelite for long distance TV transmission because
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a)T.V. signals has short wave length
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b) TV signal has long wavelength
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c)TV signal has light signals
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d)TV signals are not reflected by ionosphere
Explanation
Answer: (d)
Q.4
Which of the following waves have the maximum wavelength .. [ AFMC 2002]
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a)Infrared rays
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b) UV rays
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c)Radio waves
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d)X-rays
Explanation
Radio waves are low frequency electromagnetic waves. So their wave length will be comparatively large Answer: (c)
Q.5
Which scientist experimentally proved the existence of electromagnetic wave. [ AFMC 2004]
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a) Sir J.C Bose
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b) Maxwell
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c)Marconi
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d)Hertz
Explanation
Answer: (d)
Q.6
The direction of propagation of electromagnetic waves is given by the direction of ..[ AFMC 2011]
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a)Vector E
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b) Vector B
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c)Vector (E × B )
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d)none of these
Explanation
Electric and magnetic field vectors are perpendicular to direction of propagation Answer:(c)
Q.7
If the magnetic field of a light wave oscillates parallel to y-axis and is given by By=Bmsin(kz-ωt), the direction of wave travel and the axis along which the electric vector oscillates is .. [ AIIMS 2011]
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a) +ve y-axis, z-axis
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b) -ve z-axis , x-axis
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c) -ve x axis , y-axis
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d) -ve x axis, z-axis
Explanation
According to given equation wave is propagating along z axis . Direction of electric field must be perpendicular to both direction of propagation and magnetic field. so electric field must be along x-axis Answer: (b)
Q.8
A TV tower has height of 100m. How much population is covered by the TV broadcast if the average population density around the tower is 1000km-2> ( radius of earth=6.37× 106m) [ AFMC 2009]
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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
d=√(2hR) Population covered=πd2×population density=3.14×2hR×1000×( 10-3)2=3.14×2×100×6.37×106×1000×10-6=40 lakhsAnswer: (d)
Q.9
Ozone layer in atmosphere is, useful, because it... [ AFMC 2007]
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a) stops ultraviolet radiation
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b) absorbs pollutant gases
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c)stops green house effect
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d)stops increase in temperature of atmosphere
Explanation
Ozone layer in atmosphere is useful because it absorbs ultraviolet radiationAnswer: (a)
Q.10
According to Maxwell's hypothesis, changing of electric filed give rise to.. [ AIIMS 1999]
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a) magnetic filed
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b) pressure gradient
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c)charge
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d)voltage
Explanation
Changing of electric field produces displacement current which produces magnetic filed. So, changing electric field produces magnetic filed Answer:(a)
Q.11
In communication with the help of antenna if height is double then the range covered which was initially 'r' would become
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a) (√2)r
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b) 3r
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c) 4r
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d) 5r
Explanation
Range of antenna=r√(2hr), h=height of antenna, R=radius of earth If h is doubled i.e. h'=2h , then new range r'=√(2hr') r'=√(2.2hr)=√2 ×√(2hr)=√2(r) Answer: (a)
Q.12
Communication on ground is through electromagnetic waves of wavelength [ AIIMS 2010]
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a)larger than 600 m
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b) between 200 and 600 m
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c)between 1 and 5 m
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d)between 10-3 and 0.1
Explanation
Answer: (d)
Q.13
If the highest modulating frequency of the wave is 5kHz, the number of stations that can be accommodated in a 150kHz band width are .. [ AIIMS 2007]
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a) 15
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b) 10
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c)5
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d)none of these
Explanation
In case of complex audio signal bandwidth=2× maximum frequency of modulating signalBand with for single c=2×5 kHz=10 kHzNumber of stations=Total B.W / B.W. of each channel=150 /10=15Answer: (a)
Q.14
) If intensity of wave is 0.03W/m2, energy density of radiation is ... C=3×108 m/s
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a) 106 J m-3
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b) 10-6 J m-3
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c)10-10 J m-3
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d)1010 J m-3
Explanation
Intensity (I)=energy density(ρ) ×Velocity of light(C)0.03=ρ(3×108)∴ ρ=10-10 Jm-3 Answer:(c)
Q.15
) If energy in form of electromagnetic waves being incident on the surface is U, momentum gained by the surface is ... ( Energy is completely absorbed by the surface)
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a) p=U2 / C
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b) p=U / C2
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c) p=U/C
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d) p=2U/ C
Explanation
Momentum gain by the surface p=U/C Answer: (c)
Q.16
The electromagnetic radiation is caused by.. [ CBSE-PMT 1999]
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a) stationary charge
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b) uniformly moving charges
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c)accelerated charges
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d)all of above
Explanation
Answer: (c)
Q.17
The oscillating electric and magnetic field vectors of electromagnetic eave are oriented along.. [ CBSE-PMT 1994]
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a)the same direction and in phase
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b) the same direction but have a phase difference of 90°
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c)mutually perpendicular directions and are in phase
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d)mutually perpendicular directions but has a phase difference of 90°
Explanation
the direction of oscillations of E and B fields are perpendicular to each other as well as to the direction of propagation. So, electromagnetic waves are transvere in nature. the electric and magnetic fields oscillate in same phaseAnswer: (c)
Q.18
The electric and magnetic field of an electromagnetic wave are... [ CBSE-PMT 2007]
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a) in opposite phase and perpendicular to each other
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b) in opposite phase and parallel to each other
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c)in phase and perpendicular to each other
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d)in pahse and parallel to each other
Explanation
Answer:(c)
Q.19
If E and B represent electric and magnetic field vectors of the electromagnetic waves, then the direction of propogation of the waves will be along.. [ CBSE-PMT 2002]
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a) B × E
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b) E
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c) B
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d) E×B
Explanation
Direction of propagation of electro-magnetic waves is perpendicular to Electric field and Magnetic field. Hnece, direction is given by Pointing Vector S=E×H=E×B / µo Answer: (d)
Q.20
Which of the following statement is false for the properties of electromagnetic waves? [ CBSE-pMT 2010]
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a)Both electric and magnetic field vector attain the maxima and minimuma at the same place and same time
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b) the energy in electromagnetic wave divided equally between electric and magnetic vectors
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c)Both electric and magnetic vectors are parallel to each other and perpendicular to the direction of propagation
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d)these wave do not require any material medium for propagation
Explanation
Electromagnetic waves are the combination of mutually perpendicular electric and magnetic fields. So, option (c) is falseAnswer: (c)
Q.21
Which one of the following ray is not electromagnetic wave? [ CBSE-PMT2003]
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a) heat rays
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b) X-rays
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c) γ-rays
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d) β-rays
Explanation
β rays are stream of electrons Answer: (d)
Q.22
) A gold leaf electroscope is charged and the leaves are observered to diverge by a certain amount. A beam of X-rays is allowed to fall upon the electroscope for short periode. The leaves would
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a)collapse
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b) melt
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c)diverge more
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d)remains at same divergence
Explanation
Answer: (d)
Q.23
The density of air at the top of mesosphere in comparison to that of near the earth's surface is
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a) 10-3
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b) 10-5 times
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c)103 times
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d) 105 times
Explanation
Answer: (b)
Q.24
The density of air the top of stratosphere in comparison to that of near the earth's surface is
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a) 10-2 times
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b) 10-5 times
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c)102 times
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d)103 times
Explanation
Answer:(b)
Q.25
The shortest wavelength of X-ray emitted from an X-ray tube depends upon
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a) nature of the gas in the tube
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b) voltage applied to tube
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c) current in the tube
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d) nature of traget of the tube
Explanation
Answer: (b)
Q.26
Whose experiemts mark the begining of the field of communication using electromagnetic waves
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a)Maxwell
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b) Hertz
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c)Marconi
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d)J.CBose
Explanation
Answer: (c)
Q.27
Ground waves have a wavelength
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a) less than 200 m
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b) equal to 200 m
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c)more than 200 m
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d)all of these
Explanation
Answer: (c)
Q.28
Radiowaves with frequencies higher than television signals are
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a) ultrasonic waves
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b) sound waves
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c)infrasonic waves
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d)microwaves
Explanation
Answer:(d)
Q.29
The production of X-rays is a phenomenon for the conservation of
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a) mass into potential energy
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b) mass into heat
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c) kinetic energy into radiant energy
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d) charge
Explanation
Answer: (c)
Q.30
Radiowaves do not penetrate in the region of
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a)ionosphere
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b) mesosphere
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c)troposphere
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d)statosphere
Explanation
Answer: (a)
0 h : 0 m : 1 s
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