Physics MCQs for Class 12 Chapter 8 Electromagnetic Waves

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MCQs on Class 12 Physics Chapter 8 Electromagnetic Waves

Q.1. In electromagnetic waves the phase difference between electric and magnetic field vectors are
(a) zero
(b)Β πœ‹/4
(c)Β πœ‹/2
(d) Ο€

Answer Answer:
(a) Electric and magnetic field vectors always vary in same phase.

Q.2. Which of the following has minimum wavelength?
(a) Blue light
(b) Ξ³-rays
(c) infrared rays
(d) microwave

Answer Answer:
(b) Ξ³-rays have maximum frequency so minimum wavelength among electromagnetic waves.

Q.3. The correct option, if speeds of gamma rays, X-rays and microwave are Vg, Vx an Vm respectively will be.
(a) Vg > Vx > Vm
(b) Vg < Vx < Vm
(c) Vg > V> Vm
(d) Vg = Vx = Vm

Answer Answer:
(d) All electromagnetic waves travel with the speed of light in space.

Q.4. Which of the following has maximum penetrating power?
(a) Ultraviolet radiation
(b) Microwaves
(c) Ξ³-rays
(d) Radio waves

Answer Answer:
(c) Ξ³-rays have maximum frequency and energy of proton, therefore maximum penetrating power.

Q.5. Electromagnetic waves travelling in a medium having relative permeability ΞΌr = 1.3 and relative permittivity Er = 2.14. The speed of electromagnetic waves in medium must be
(a) 1.8 Γ— 108 ms-1
(b) 1.8 Γ— 104ms1
(c) 1.8 Γ— 106ms1
(d) 1.8 Γ— 10Β² ms-1

Answer Answer:
(a)


Q.6. The quantity βˆšπœ‡0πœ€0 represents
(a) speed of sound
(b) speed of light in vacuum
(c) speed of e.m. waves
(d) inverse of speed of light in vacuum

Answer Answer:
(d)

Q.7. In electromagnetic wave if ue and um are mean electric and magnetic energy densities respectively, then
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 5

Answer Answer:
(a) Energy is equally distributed among electric field and magnetic field

Q.8. Which of the following is called heat radiation?
(a) X-rays
(b) Ξ³-rays
(c) Infrared radiation
(d) Microwave

Answer Answer:
(c)

Q.9. From Maxwell’s hypothesis, a charging electric field gives rise to
(a) an electric field.
(b) an induced emf.
(c) a magnetic field.
(d) a magnetic dipole.

Answer Answer:
(c) A charging electric field gives rise to a magnetic field.

Q.10. The ultra high frequency band of radio waves in electromagnetic wave is used as in
(a) television waves
(b) cellular phone communication
(c) commercial FM radio
(d) both (a) and (c)

Answer Answer:
(b)

Q.11. Electromagnetic waves are transverse in nature is evident by
(a) polarisation.
(b) interference,
(c) reflection.
(d) diffraction.

Answer Answer:
(a) Only transverse waves can be polarised.

Q.12. Which of the following are not electromagnetic waves?
(a) Cosmic rays
(b) Ξ³-rays
(c) Ξ²-rays
(d) X-rays

Answer Answer:
(c) Ξ²-rays consists of electrons which are not electromagnetic nature.

Q.13. 10 cm is a wavelength corresponding to the spectrum of
ia) infrared rays
(b) ultraviolet rays
(c) microwaves
(d) X-rays

Answer Answer:
(c) Microwaves have wavelength around 10 cm.

Q.14. If πΈβƒ—  and π΅βƒ—  represent electric and magnetic field vector of the electromagnetic waves then the direction of propagation of the em wave is that of
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 6

Answer Answer:
(c) 𝐸⃗ ×𝐡⃗

Q.15. The structure of solids is investigated by using
(a) cosmic rays
(b) X-rays
(c) Ξ³-rays
(d) infrared rays

Answer Answer:
(b) X-rays are used to investigate structure of solids.

Q.16.. The condition under which a microwave over heats up a food item containing water molecules most efficiently is
(a) The frequency of the microwaves must match the resonant frequency of the water molecules.
(b) The frequency of the microwaves has no relation with natural frequency of the water molecules.
(c) Microwaves are heat waves, so always produce heating.
(d) Infrared waves produce heating in a microwave oven.

Answer Answer:
(a) When frequency of microwave matches with frequency of water molecules i.e., resonant condition. Maximum energy is transferred to water molecules as their K.E. energy.

Q.17. Which radiations are used in treatment of muscle ache?
(a) Infrared
(b) Ultraviolet
(c) Microwave
(d) X-rays

Answer Answer:
(a) Infrared radiations are used in the treatment of muscle ache.


Q.18. Waves in decreasing order of their wavelength are
(a) X-rays, infrared rays, visible rays, radio waves
(b) radio waves, visible rays, infrared rays, X-rays.
(c) radio waves, infrared rays, visible rays, X-rays.
(d) radio waves, ultraviolet rays, visible rays, X-rays.

Answer Answer:
(c)

Q>19. The electric field associated with an e.m wave in vacuum is given by πΈβƒ—  =40 cos (kz – 6 Γ— 108t) π‘–βƒ— , where E, Z and t are in volt/m, metre and seconds respectively. The value of wave vector K is
(a) 2 m-1
(b) 0.5 m-1
(c) 6 m-1
(d) 3 m-1

Answer Answer:
(a) Wave vector, π‘˜=π‘ŠπΆ=6Γ—108/3Γ—108=2 mβˆ’1

Q.20. Electromagnetic waves with wavelength Ξ» are used by a FM radio station for broadcasting. Here Ξ» belongs to
(a) radio waves
(b) VHF radio waves
(c) UHF radio waves
(d) microwaves

Answer Answer:
(b)

Q.21. The oscillating magnetic field in a plane electromagnetic wave is given as By = (8 Γ— 10-6) sin [2 Γ— 1011t+ 300Ο€x] T, wavelength of the em wave is
(a) 0.80 cm
(b) 1 Γ— 103m
(c) 2 Γ— 10-2cm
(d) 0.67 cm

Answer Answer:
(d) wavelength πœ†=2πœ‹300πœ‹=1150m = 0.67 cm

Q.22. Maxwell in his famous equations of electromagnetism introduced the concept of
(a) ac current
(b) displacement current
(c) impedance
(d) reactance

Answer Answer:
(b)

Q.23. The conduction current is same as displacement current when source is
(a) ac only
(b) dc only
(c) either ac or dc
(d) neither dc nor ac

Answer Answer:
(c)

Q.24. If a variable frequency ac source is connected to a capacitor then with decrease in frequency the displacement current will
(a) increase
(b) decrease
(c) remains constant
(d) first decrease then increase

Answer Answer:
(b)

Q.25. An electromagnetic wave can be produced, when charge is
(a) moving with a constant velocity
(b) moving in a circular orbit
(c) falling in an electric field
(d) both (b) and (c)

Answer Answer:
(d)

Q.26. Which of the following statement is false for the properties of electromagnetic waves?
(a) Both electric and magnetic field vectors attain the maxima and minima at the same place and same time.
(b) The energy in electromagnetic waves is divided equally between electric and magnetic field vectors.
(c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave.
(d) These waves do not require any material medium for propagation.

Answer Answer:
(c)

Q.27. Which of the following has/have zero average value in a plane electromagnetic wave?
(a) Both magnetic and electric fields
(b) Electric field only
(c) Magnetic field only
(d) None of these

Answer Answer:
(a)

Q.28. A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The frequency of electromagnetic waves produced by the oscillator is
(a) 106 Hz
(b) 107 Hz
(c) 108 Hz
(d) 109 Hz

Answer Answer:
(d)

Q.29. If E and B denote electric and magnetic fields respectively, which of the following is dimensionless?
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves

Answer Answer:
(a)


Q.30. The waves used by artificial satellites for communication is
(a) microwaves
(b) infrared waves
(c) radio waves
(d) X-rays

Answer Answer:
(a)

Q.31. Which of the following electromagnetic waves is used in medicine to destroy cancer cells?
(a) IR-rays
(b) Visible rays
(c) Gamma rays
(d) Ultraviolet rays

Answer Answer:
(c)

Q.32. A linearly polarized electromagnetic wave given as E = E0 π‘–Μ‚  cos (kz – Ο‰t) is incident normally on a perfectly reflecting infinite wall at z = a. Assuming that the material of the wall is optically inactive, the reflected wave will be given as [NCERT Exemplar]
(a) Er = -E0 π‘–Μ‚  cos (kz – Ο‰t).
(b) Er = E0 π‘–Μ‚  cos (kz + Ο‰t).
(c) Er = -E0 π‘–Μ‚  cos (kz + Ο‰t).
(d) Er = E0 π‘–Μ‚  sin (kz – Ο‰t).

Answer Answer:
(b)

Q.33. Light with an energy flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 30 cm2, the total momentum delivered (for complete absorption) during 30 minutes is , [NCERT Exemplar]
(a) 36 Γ— 10-5 kg m/s.
(b) 36 Γ— 10-4 kg m/s.
(c) 108 Γ— 104 kgm/s.
(d) 1.08 Γ— 107 kg m/s.

Answer Answer:
(b)

Q.34. The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is [NCERT Exemplar]
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 2

Answer Answer:
(d)

Q.35. If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along [NCERT Exemplar]
(a) E.
(b) B.
(c) B Γ— E.
(d) E Γ— B.

Answer Answer:
(d)

Q.36. Which of the following statement is false for the properties of em waves?
(a) The energy of em wave is divided equally between electric and magnetic fields.
(b) Both electric and magnetic field vectors are parallel to each and perpendicular to the direction of propagation of wave.
(c) These waves do not require any material medium for propagation.
(d) Both electric and magnetic field vectors attain the maximum and minimum at the same place and same time.

Answer Answer:
(b) Electric and magnetic field vectors are mutually perpendicular to each other directed along the propagation of wave.

Q.37. An EM wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the [NCERT Exemplar]
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 3

Answer Answer:
(c)


Q.38. An electromagnetic wave travelling along z-axis is given as-E=E0 cos (kz – πœ”t). Choose the incorrect option from the following;
(a) The associated magnetic field is given as B = 1π‘π‘˜Μ‚  Γ— E = 1πœ”(π‘˜Μ‚  Γ— E)
(b) The electromagnetic field can be written in terms of the associated magnetic field as E = c(B Γ— π‘˜Μ‚ )
(c) π‘˜Μ‚ .E = 0, π‘˜Μ‚ .B =0.
(d) π‘˜Μ‚  Γ— E = 0, kπ‘˜Μ‚  Γ— B = 0.

Answer Answer:
(d)

Q.39. A plane electromagnetic wave propagating along x direction can have the following pairs of E and B
(a) Ex,By.
(b) Ey, Bz.
(c) Bx, Ey.
(d) None of these

Answer Answer:
(b)

Q.40. A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. For producing electromagnetic waves which one is not true?
(a) They will have frequency of 109 Hz.
(b) They will have frequency of 2 Γ— 109 Hz.
(c) They will have a wavelength of 0.3 m.
(d) They fall in the region of radio waves.

Answer Answer:
(b)

Q.41. The source of electromagnetic waves can be a charge
(a) moving with a constant velocity.
(b) moving in a circular orbit.
(c) at rest.
(d) falling in a magnetic field.

Answer Answer:
(b)

Q.42. One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in [NCERT Exemplar]
(a) visible region.
(b) infrared region.
(c) ultraviolet region.
(d) microwave region.

Answer Answer:
(c)

Q.43. The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is [NCERT Exemplar]
(a) c : 1
(6) cΒ² : 1
(c) 1 : 1
(d) √c : 1

Answer Answer:
(c)

Q.44. An electromagnetic wave travels in vacuum along z direction: E = (E1i + E2j) cos(kz – πœ”t). Choose the correct options from the following:
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 4
(c) The given electromagnetic field is circularly polarised.
(d) The given electromagnetic wave is unpolarised.

Answer Answer:
(a)

Q.45. Speed of electromagnetic wave related to electric field and magnetic field vector in vacuum.
Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves 7

Answer Answer:
(a)

Q.46. An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following is not true? [NCERT Exemplar]
(a) Radiation pressure is I/c if the wave is totally absorbed.
(b) Radiation pressure is I/c if the wave is totally reflected.
(c) Radiation pressure is 2I/c if the wave is totally reflected.
(d) Radiation pressure is in the range I/c < p < 2I/c for real surfaces.

Answer Answer:
(b)


Q.47. In electromagnetic spectrum, the frequencies Ξ³-rays, X-rays and ultraviolet rays are denoted by n1, n2 and n3 respectively then
(a) n1 > n2 > n3
(b) n1 < n2 < n3
(c) n1 > n2 < n3
(d) n1 < n2 > n3

Answer Answer:
(a) From electromagnetic spectrum, frequencies of Ξ³-rays is greater than frequency of X-rays. Frequency of Xrays is greater than frequency of ultraviolet rays.

Q.48. Which one of the following has the shortest wavelength?
(a) Infrared rays
(b) Ultraviolet rays
(c) Microwaves
(d) Gamma rays

Answer Answer:
(d)

Q.49. When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity i.e. dielectric constant of the ionised layer
(a) does not change
(b) appears to increase
(c) appears to decrease
(d) sometimes appears to increase and sometimes to decrease

Answer Answer:
(c)

Q.50. Ultraviolet rays coming from sun are absorbed by
(a) troposphere
(b) ionosphere
(c) stratosphere
(d) mesosphere

Answer Answer:
(b)

Q.51. The EM waves when travel into different media gets
(a) refracted
(b) transmitted
(c) reflected
(d) emitted

Answer Answer:
(c)

Q.52. The absorption of radio waves by the atmosphere depends upon
(a) their velocities
(b) their frequencies
(c) their distance from the transmitter
(d) None of these

Answer Answer:
(a)

Q.53. The velocity of all radio waves in free space is 3 Γ— 108 m/s. The frequency of a radio wave of wavelength 150m is
(a) 20 kHz
(b) 2 kHz
(c) 2 MHz
(d) 1 MHz

Answer Answer:
(c) Hint: f=v/Ξ»

Q.54. The polarisation of electromagnetic wave is in
(a) the directions of electric and magnetic field
(b) the directions of electric field
(c) the direction of magnetic field
(d) can not be polarized

Answer Answer:
(b)

Q.55. If the frequency of EM radiations is halved then the energy of EM radiation will become
(a) double
(b) remains unchanged
(c) becomes half
(d) becomes one fourth

Answer Answer:
(c)

Q.56. Microwaves are electromagnetic waves with frequency in the range of
(a) Micro hertz
(b) Giga hertz
(c) Mega hertz
(d) Hertz

Answer Answer:
(b)

Q.57. For television broadcasting the frequency employed is normally
(a) 30-300 MHz
(b) 30-300 GHz
(c) 30-300 kHz
(d) 30-300 Hz

Answer Answer:
(a)

Q.58. Electromagnetic waves of frequency …. are reflected from ionosphere.
(a) 100 MHz
(b) 2 MHz to 80 MHz
(c) upto 1.5 MHz
(d) less than 1.5 MHz

Answer Answer:
(b)

Q.59. When an electromagnetic wave enters an ionised layer of earth’s atmosphere present in ionosphere
(a) the electron cloud will not oscillate in the electric field of the wave
(b) the electron cloud will oscillate in the electric field of wave in the phase of sinusoidal electromagnetic wave
(c) the electron cloud will oscillate in the electric field of wave in the opposite phase of sinusoidal
electromagnetic wave
(d) the electron cloud will oscillate in the electric field of wave with a phase retardation of 90Β° for a sinusoidal electromagnetic wave.

Answer Answer:
(d)

Q.60. An electron oscillating with a frequency of 3 Γ— 106 Hz, would generate
(a) X-rays
(b) ultraviolet rays
(c) radio waves
(d) microwaves

Answer Answer:
(c)

Q.61. Ultraviolet spectrum can be studied by using a
(a) flint glass prism
(b) direct vision prism
(c) nicol prism
(d) quartz prism

Answer Answer:
(d)

Q.62. The cellular mobile radio frequency band is
(a) 88 – 108 MHz
(b) 54 – 72 MHz
(c) 540 – 1600 KHz
(d) 840 – 935 MHz

Answer Answer:
(d)

Q.63. Select the wrong statement. EM waves
(a) are transverse in nature.
(b) travel in free space at a speed of light.
(c) are produced by accelerating charges.
(d) travel in all media with same speed.

Answer Answer:
(d)

Q.64. The ozone layer in the atmosphere absorbs
(a) only the radiowaves
(b) only the visible light
(c) only the Ξ³-rays
(d) X-rays and ultraviolet rays

Answer Answer:
(d)

Q.65. The waves which are electromagnetic in nature are
(a) sound waves and light waves
(b) water waves and radio waves
(c) light waves and X-rays
(d) sound waves and water waves

Answer Answer:
(c) Light waves and X-rays are electromagnetic waves.

Q.66. Which one of the following has the maximum energy?
(a) Radio waves (b) Infrared rays
(c) Ultraviolet rays (d) Micro waves

Answer Answer:
(c)

Q.67. Ozone layer above earth’s atmosphere will not
(a) prevent infrared radiations from sun reaching earth.
(b) prevent infra red radiations originated from earth from escaping earth’s atmosphere.
(c) prevent ultraviolet rays from sun.
(d) reflect back radio waves.

Answer Answer:
(d) Ozone layer will absorb ultraviolet rays; reflect the infrared radiation and does not reflect back radiowaves.

Q.68. Which of the following is/are true for electromagnetic waves?
I. They transport energy.
II. They have momentum.
III. They travel at different speeds in air depending on their frequency.
(a) I and III (b) II only
(c) I, II and III (d) I and II

Answer Answer:
(c)

Q.69. The amplitude of an electromagnetic wave in vacuum is doubled with no other changes made to the wave. As a result of this doubling of the amplitude, which of the following statements are incorrect?
I. The speed of wave propagation chages only
II. The frequency of the wave changes only
III. The wavelength of the wave changes only
(a) I and II (b) II and III
(c) I and III (d) I, II and III

Answer Answer:
(d)

Q.70. Select the correct statement(s) from the following.
I. Wavelength of microwaves is greater than that of ultraviolet rays.
II. The wavelength of infrared rays is lesser than that of ultraviolet rays.
III. The wavelength of microwaves is lesser than that of infrared rays
IV. Gamma ray has shortest wavelength in the electromagnetic spectrum
(a) I and II (b) II and III
(c) III and IV (d) I and IV

Answer Answer:
(d)

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