Electromagnetic Waves PYQs Set 3 (PDF)

Set 3 of 9 · Questions 61-90 of 253

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Mere Teacher · Previous Year Questions JEE Main Physics · Electromagnetic Waves · Set 3 (Q61-90)
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61. $In a plane electromagnetic wave, the electric field oscillates with a frequency 2 \times 10^{10} s^{- 1} and amplitude 40 Vm^{- 1}, then the energy density due to electric field is (ϵ_{0} = 8.85 \times 10^{- 12} Fm^{- 1})$ (1) $1.52 \times 10^{- 9} Jm^{- 3}$ (2) $2.54 \times 10^{- 19} Jm^{- 3}$ (3) $3.54 \times 10^{- 9} Jm^{- 3}$ (4) $4.56 \times 10^{- 9} Jm^{- 3}$ 62. $In Young's double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes [NEET 2020]$ (1) $half$ (2) $four times$ (3) $one-fourth$ (4) $double$ 63. $The electric field of an electromagnetic wave in free space is represented as E = E_{0} cos (ωt - kz) i . The corresponding magnetic induction vector will be :$ (1) $B = E_{0} C cos (ωt - kz) j$ (2) $B = \frac{E _{0}}{C} cos (ωt - kz) j$ (3) $B = E_{0} Cos (ωt + kz) j$ (4) $B = \frac{E _{0}}{C} cos (ωt + kz) j$ 64. $We consider the radiation emitted by the human body. Which one of the following statements is true?$ (1) $The radiation emitted is in the infrared region$ (2) $The radiation is emitted only during the day$ (3) $The radiation is emitted during the summers and absorbed during the winters$ (4) $The radiation emitted lies in the ultraviolet region and hence is not visible$ 65. $In a plane EM wave, the electric field oscillates sinusoidally at a frequency of 5 \times 10^{10} Hz and an amplitude of 50 Vm^{- 1} . The total average energy density of the electromagnetic field of the wave is : [Use (ϵ_{0} = 8.85 \times 10^{- 12} C^{2} / Nm^{2})$ (1) $1.106 \times 10^{- 8} Jm^{- 3}$ (2) $4.425 \times 10^{- 8} Jm^{- 3}$ (3) $2.212 \times 10^{- 8} Jm^{- 3}$ (4) $2.212 \times 10^{- 10} Jm^{- 3}$ 66. $X-rays, gamma rays and microwaves travelling in vacuum have$ (1) $same wavelengths but different velocities$ (2) $same frequency but different velocities$ (3) $same velocity but different wavelengths$ (4) $same velocity and same frequency.$ 67. $The relation between permittivity of free space, the permeability of free space and speed of light is$ (1) $ϵ_{0} μ_{o} = \frac{4 π}{C ^{2}}$ (2) $ϵ_{o} μ_{o} = \frac{1}{C ^{2}}$ (3) $ϵ_{o} μ_{o} = \frac{1}{C}$ (4) $ϵ_{0} μ_{o} = c^{2}$ 68. $About 20 % of the power of a 100 W bulb is converted to visible radiation. Assuming that the radiations is emitted isotropically and neglecting reflection, the average intensity of visible radiation at a distance of 5 m is \frac{α}{25 π} W / m^{2} . The value of α is$ (1) $15$ (2) $5$ (3) $37.5$ (4) $30$ 69. $An object is placed in a medium of refractive index 3 . An electromagnetic wave of intensity falls normally on the object and it is absorbed completely. The radiation pressure on the object would be (speed of light in free space :$ (1) $36 Nm^{- 2}$ (2) $18 Nm^{- 2}$ (3) $6 Nm^{- 2}$ (4) $2 Nm^{- 2}$ 70. $When a metal target is bombarded with high energy electrons, the electromagnetic waves generated are$ (1) $infrared waves$ (2) $microwaves$ (3) $X-rays$ (4) $gamma rays$ 71. $The electric field in a plane electromagnetic wave is given by : E_{y} = 69 sin (0.6 \times 10^{3} x - 1.8 \times 10^{11} t) V / m . The expression for magnetic field associated with this electromagnetic wave is____Т.$ (1) $Bz=2.3\times 1 0^{- 7} sin0.6\times103x-1.8\times1011t$ (2) $Bz=2.3\times 1 0^{- 7} sin0.6\times103x+1.8\times1011t$ (3) $B_{y} = 69 sin (0.6 \times 10^{3} x + 1.8 \times 10^{11} t)$ (4) $By=2.3\times 1 0^{- 7} sin0.6\times103x-1.8\times1011t$ 72. $A flashlight of intensity 9 W / cm^{2} illuminates a perfectly reflective surface of area 300 cm^{2} . The average force exerted on the surface due to the incident light photons is$ (1) $0 N$ (2) $14 μ N$ (3) $18 μ N$ (4) $12 μ N$ 73. $The average power output of a point source of an electromagnetic radiation is 1080 W . The maximum value of the rms value of the electric field at a distance of 3 m from the source is$ (1) $20 Vm^{- 1}$ (2) $40 Vm^{- 1}$ (3) $60 Vm^{- 1}$ (4) $90 Vm^{- 1}$ 74. $An electric charge oscillating harmonically with frequency 750 kHz produces electromagnetic waves of frequency (Speed of light in vacuum is 3 \times 10^{8} ms^{- 1})$ (1) $250 kHz$ (2) $500 kHz$ (3) $750 kHz$ (4) $1000 kHz$ 75. $The energy associated with electric field is (U_{E}) and with magnetic fields is (U_{B}) for an electromagnetic wave in free space. Then:$ (1) $U_{E} = U_{B} 2$ (2) $U_{E} > U_{B}$ (3) $U_{E} < U_{B}$ (4) $U_{E} = U_{B}$ 76. $he electric field in an electromagnetic wave is given by E = 56.5sin ω (t - x/c) N C^{- 1} . Find the intensity of the wave if it is propagating along x-axis in the free space. (Given ϵ_{0} = 8.85 \times 1 0^{- 12} C^{2} N^{- 1} m^{- 2})$ (1) $5.65 W m^{2}$ (2) $4.24 W m^{- 2}$ (3) $1.9 x 1 0^{7} W m^{- 2}$ (4) $56.5 W m^{- 2}$ 77. $A laser beam has intensity 2.1 \times 10^{15} W / m^{2} . The amplitude of magnetic field in the beam in approximately is$ (1) $1.4 T$ (2) $4.2 T$ (3) $1 T$ (4) $1.5 T$ 78. $On a particular day, the sun delivers an average power of (\frac{6}{π} \times 10^{3}) \frac{W}{m ^{2}} to the top of Earth's atmosphere. Find the amplitude of magnetic field for the electromagnetic waves above atmosphere. (Take μ_{0} = 4 π \times 10^{- 7} SI unit)$ (1) $5 \times 10^{- 5} T$ (2) $4 \times 10^{- 6} T$ (3) $6 \times 10^{- 6} T$ (4) $3 \times 10^{- 5} T$ 79. $A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?$ (1) $The angular width of the central maximum of the diffraction pattern will increase.$ (2) $The angular width of the central maximum will decrease.$ (3) $The angular width of the central maximum will be unaffected.$ (4) $Diffraction pattern is not observed on the screen in the case of electrons.$ 80. $Suppose that the electric field amplitude of electromagnetic wave is I_{0} = 120 NC^{- 1} and its frequency is f * 50 MH z . Then which of the following value is incorrectly computed?$ (1) $Magnetic field amplitude is 400 nT .$ (2) $Angular frequency of electromagnetic wave is π \times 10^{8} rad / s .$ (3) $Propagation constant (angular wave number) is 2.1 rad / m .$ (4) $Wavelength of electromagnetic wave is 6 m .$ 81. $If E_{o} and B_{o} are the magnitudes of the electric and magnetic fields respectively of an electromagnetic wave in vacuum, then among the following the correct relation is (μ_{o} - permeability of free space, ϵ_{o} - permittivity of free space)$ (1) $E_{o} = B_{o} μ_{o} ϵ_{o}$ (2) $E_{o} ϵ_{o} = B_{o} μ_{o}$ (3) $E_{o} ϵ_{o} = \frac{B _{o}}{μ _{0}}$ (4) $\frac{E _{o}}{ϵ _{o}} = \frac{B _{o}}{μ _{0}}$ 82. $In a travelling plane electromagnetic wave, the maximum magnetic field is 1.26 \times 10^{- 4} T . The intensity of the wave is (Assume, μ_{0} = 1.26 \times 10^{- 6} H / m)$ (1) $1.56 \times 10^{6} \frac{W}{m ^{2}}$ (2) $1.89 \times 10^{6} \frac{W}{m ^{2}}$ (3) $8.92 \times 10^{5} \frac{W}{m ^{2}}$ (4) $4.62 \times 10^{6} \frac{W}{m ^{2}}$ 83. $An alternating voltage of amplitude 40 V and frequency 4 kHz is applied directly across the capacitor of 12 μ F . The maximum displacement current between the plates of the capacitor is nearly :$ (1) $10 A$ (2) $12 A$ (3) $8 A$ (4) $13 A$ 84. $All electromagnetic wave is transporting energy in the negative z direction. At a certain point and certain time the direction of electric field of the wave is along positive y direction. What will be the direction of the magnetic field of the wave at that point and instant?$ (1) $Positive direction of x$ (2) $Positive direction of z$ (3) $Negative direction of x$ (4) $Negative direction of y$ 85. $In the given electromagnetic wave E_{y} = 600 sin (ω t - kx) Vm^{- 1}, intensity of the associated light beam is (in W / m^{2} : (Given (ϵ_{0} = 9 \times 10^{- 12} C^{2} N^{- 1} m^{- 2})$ (1) $243$ (2) $729$ (3) $972$ (4) $486$ 86. $If the amplitude of the magnetic field in a travelling plane electromagnetic wave is 2.2 \times 10^{- 4} T, then the intensity of the wave is nearly$ (1) $5.8 \times 10^{6} Wm^{- 2}$ (2) $4.2 \times 10^{6} Wm^{- 2}$ (3) $1.2 \times 10^{7} Wm^{- 2}$ (4) $8.8 \times 10^{5} Wm^{- 2}$ 87. $Electromagnetic waves of energy flux 75 \times 10^{4} Wm^{- 2} incidents normally on a surface of area 40 cm^{2} . If absorbs the surface the flux completely, the total momentum delivered to the surface in one second is$ (1) $10^{- 2} kgms^{- 1}$ (2) $10^{- 3} kgms^{- 1}$ (3) $10^{- 4} kgms^{- 1}$ (4) $10^{- 5} kgms^{- 1}$ 88. $An electromagnetic wave of frequency 3GHz enters a dielectric medium of relative electric permittivity 2.25 from vacuum. The wavelength of this wave in that medium will be ____\times 10^{- 2} cm$ 89. $A common transistor radio set requires 12 V (D.C.) for its operation. The D.C. source is constructed by using a transformer and a rectifier circuit, which are operated at 220 V (A.C.) on standard domestic A.C. supply. The number of turns of secondary coil are 24, then the number of turns of primary are ____.$ 90. $An electromagnetic wave of frequency 5GHz, is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are 2. Its velocity in this medium is _______\times 10^{7} m/s.$