# Physics MCQs for Class 12 with Answers Chapter 8 Electromagnetic Waves

Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 8 Electromagnetic Waves. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. Students can solve NCERT Class 12 Physics Electromagnetic Waves MCQs Pdf with Answers to know their preparation level.

## Electromagnetic Waves Class 12 Physics MCQs Pdf

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

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

2. Which of the following has maximum penetrating power?
(b) Microwaves
(c) γ-rays

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

3. Electromagnetic waves travelling in a medium having relative permeability μr = 1.3 and relative permittivity Er = 2.14. The speed of electromagnetic waves in medium must be
(a) 1.8 × 108 ms-1
(b) 1.8 × 104ms1
(c) 1.8 × 106ms1
(d) 1.8 × 10² ms-1

Explaination: (a) speed of emw

4. In electromagnetic waves the phase difference between electric and magnetic field vectors are
(a) zero
(b) $$\frac{\pi}{4}$$
(c) $$\frac{\pi}{2}$$
(d) π

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

5. The quantity $$\sqrt{\mu_{0} \varepsilon_{0}}$$ represents
(a) speed of sound
(b) speed of light in vacuum
(c) speed of e.m.w.
(d) inverse of speed of light in vacuum

Explaination: (d) Speed of light in vacuum, $$c=\frac{1}{\sqrt{\varepsilon_{0} \mu_{0}}}$$

6. In electromagnetic wave if ue and um are mean electric and magnetic energy densities respectively, then

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

7. Which of the following is called heat radiation?
(a) X-rays
(b) γ-rays
(d) Microwave

8. 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.

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

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

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

10. Which of the following are not electromagnetic waves?
(a) Cosmic rays
(b) γ-rays
(c) β-rays
(d) X-rays

Explaination: (c) β-rays consists of electrons which are not electromagnetic nature.

11. 10 cm is a wavelength corresponding to the spectrum of
ia) infraredrays
(b) ultraviolet rays
(c) microwaves
(d) X-rays

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

12. If $$\vec{E}$$ and $$\vec{B}$$ represent electric and magnetic field vector of the electromagnetic waves then the direction of propagation of the em wave is that of

Explaination: (c) $$\vec{E} \times \vec{B}$$

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

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

14. 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.

Explaination:
(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.

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

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

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

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

17. 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.

18. The electric field associated with an e.m wave in vacuum is given by $$\vec{E}$$ =40 cos (kz – 6 × 108) $$\vec{i}$$, 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

Explaination:
(a) Wave vector, $$k=\frac{W}{C}=\frac{6 \times 10^{8}}{3 \times 10^{8}}=2 \mathrm{m}^{-1}$$

19. Electromagnetic waves with wavelength λ are used by a FM radio station for broadcasting. Here λ belongs to
(d) microwaves

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

Explaination:
(d) wavelength $$\lambda=\frac{2 \pi}{300 \pi}=\frac{1}{150} \mathrm{m}$$
= 0.67 cm

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

22. 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

23. 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

24. 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)

25. 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.

26. 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

27. 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

28. If E and B denote electric and magnetic fields respectively, which of the following is dimensionless?

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

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

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

32. A linearly polarized electromagnetic wave given as E = E0 $$\hat{i}$$ cos (kz – ωt) 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 $$\hat{i}$$ cos (kz – ωt).
(b) Er = E0 $$\hat{i}$$ cos (kz + ωt).
(c) Er = -E0 $$\hat{i}$$ cos (kz + ωt).
(d) Er = E0 $$\hat{i}$$ sin (kz – ωt).

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 × 10-5 kg m/s.
(b) 36 × 10-4 kg m/s.
(c) 108 × 104 kgm/s.
(d) 1.08 × 107 kg m/s.

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]

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 × E.
(d) E × B.

36. 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]

37. An electromognetic wave travels in vacuum along z direction: E = (E{i + E2j) cos(kz – cot). Choose the correct optinons from the following:

(c) The given electromagnetic field is circularly polarised.
(d) The given electromagnetic wave is unpolarised.

38. An electromagnetic wave travelling along z-axis is given as-E=E0 cos (kz – cot). Choose the incorrect option from the following;
(a) The associated magnetic field is given as B = $$\frac{1}{c}$$$$\hat{k}$$ × E = $$\frac{1}{\omega}$$($$\hat{k}$$ × E)
(b) The electromagnetic field can be written in terms of the associated magnetic field as E = c(B × $$\hat{k}$$)
(c) $$\hat{k}$$.E = 0, $$\hat{k}$$.B =0.
(d) $$\hat{k}$$ × E = 0, k$$\hat{k}$$ × B = 0.

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

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 × 109 Hz.
(c) They will have a wavelength of 0.3 m.
(d) They fall in the region of radio waves.

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.

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.

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) c² : 1
(c) 1 : 1
(d) √c : 1

44. 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.

45. Speed of electromagnetic wave related to electric field and magnetic field vector in vacuum.

46. 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.

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

47. Electromagnetic waves possess both ________ and ________ .

Explaination: energy, momentum

48. Electromagnetic waves produced by bombard ment of high energy electrons on a metal target is ________ .

Explaination: X-rays

49. Electromagnetic waves used in RADAR are ________ .

Explaination: microwaves

50. Displacement current is produced in the region of changing ________ .

Explaination: displacement current

51. Ampere-Maxwell’s law states that line integral of magnetic field along the boundary of a closed path is equal to ________ .

Explaination: μ0(Ic + Id)

52. Displacement current across a capacitor is ________ to conduction current in connecting wires.

Explaination: equal

53. Electromagnetic waves are produced by ________ electric charge.

Explaination: oscillating

54. To which part of the electromagnetic spectrum does a wave of frequency 5 × 1019 Hz belong? [AI 2014]

Explaination: The wave of frequency 5 × 1019 Hz corresponds to X-rays or γ-region of the em spectrum.

55. How are infrared waves produced? What is the range of their wavelength?

Explaination:
Infrared waves are produced by hot bodies due to the vibrations of the atoms and molecules. Their wavelength ranges from, 1 mm to 700 nm.

56. Write two uses of X-rays. [Foreign 2011]

Explaination:
(i) X-rays are used as a diagnostic tool in medicine.
(ii) X-rays are used in the treatment of certain forms of cancer.

57. How are microwaves produced? [AI 2011]

Explaination:
Microwaves are produced by special vacuum tubes like klystrons, magnetrons and gunn diodes.

58. What are the directions of electric and magnetic field vectors relative to each other and relative to the direction of propagation of electromagnetic waves?

Explaination: Mutually perpendicular.

59. Name the part of electromagnetic spectrum whose wavelength lies in the range of 10-10 m. Give its one use.

Explaination: X-rays. X-rays are used as a diagnostic tool in medicine.

60. Which part of electromagnetic spectrum has largest penetrating power?

Explaination: γ-rays.

61. What is the frequency of electromagnetic waves produced by oscillating charge of frequency v? [Delhi 2011C]

Explaination: The frequency of electromagnetic waves produced by an oscillating charge of frequency v is also v.

62. A capacitor has been charged by a dc source. What are the magnitudes of conduction and displacement currents, when it is fully charged? [Delhi 2013]

Explaination: Conduction current and displacement current both are zero.

63. How are radio waves produced? [AI 2011]

Explaination: By rapid acceleration and deceleration of electrons in conducting wires.

64. Which part of electromagnetic spectrum is absorbed from sunlight by ozone layer?

Explaination: Ultraviolet rays.

65. Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency. [AI 2013]

Explaination:
Ultraviolet rays (UV rays)
The frequency range of UV rays is 0.75 × 1015 Hz to 0.5 × 1018 Hz.

66. Name the electromagnetic radiations used for
(a) water purification, and
(b) eye surgery. [CBSE 2018]

Explaination: UV rays in both the cases.

67. Write two uses of infrared rays. [Foreign 2011]

Explaination:
(i) In electronic devices.
(ii) Infrared lamps are used in physical therapy.

68. The speed of an electromagnetic wave in a material medium is given by v = $$\frac{1}{\sqrt{\mu \varepsilon}}$$, μ being the permeability of the medium and ε its permittivity. How does its frequency change? [AI2012]

Explaination: It will remain same.

69. Name the electromagnetic waves, which
(i) maintain the Earth’s warmth, and
(ii) are used in aircraft navigation. [Foreign 2012]

Explaination: (i) Infrared (ii) Microwaves

70. How are X-rays produced? [AI 2011]

Explaination: By bombarding a metal target by high energy electrons.

71. Arrange the following electromagnetic waves in order of increasing frequency:
γ-rays, microwaves, infrared rays and ultraviolet rays. [Foreign 2014]

Explaination: γ-rays > ultraviolet rays > infrared rays > microwaves.

72. What oscillates in electromagnetic waves? Are these waves transverse or longitudinal? [CBSE Sample Paper 2011]

Explaination:
(i) The electric and magnetic fields oscillate in mutually perpendicular directions in electromagnetic waves.
(ii) Electromagnetic waves are transverse in nature.

73. Name em radiations used for detecting fake currency notes.

74. Write the expression for speed of electromagnetic waves in a medium of electrical permittivity e and magnetic permeability μ. [Foreign 2017]

Explaination:
Speed of electromagnetic waves in a medium is given by $$v=\frac{1}{\sqrt{\mu \varepsilon}}$$

75. The relative electric permittivity of a medium is 9 and the relative permeability is close to unity. What is the speed of em waves in the medium?

Explaination:

76. Let the wavelengths of the electromagnetic waves used quite often for
(i) killing germs in household water purifiers,
(ii) remote sensing
(iii) treatment of cancer, be labelled as λ1, λ2 and λ3 in increasing order. [CBSE Sample Paper 2011]

Explaination:
(ii) Microwaves (λ2),
(iii) γ-rays (λ3)
The increasing order of wavelength is λ3 < λ1 < λ2.

77. Why are microwaves used in radar?

Explaination:
Microwaves have the wavelengths of the order of a few millimetres. Due to their short wavelengths, they are not diffracted easily, and can travel longer distances.

78. Is the ratio of frequencies of ultraviolet rays and infrared rays in glass more than, less than or equal to 1?

Explaination:
More than 1, because the frequency of ultraviolet rays is greater than that of infrared rays.

79. For which frequency of light, the human eye is most sensitive?

Explaination:
Human eye is sensitive to the light of wavelength, X = 555 nm. So, its frequency is

80. What is the time period of visible light for which human eye is most sensitive?

Explaination:

81. The velocity of propagation (in vacuum) and the frequency of (i) X-rays and (ii) radiowaves are denoted by (vx, nx) and (vR, nR) respectively.
How do the values of
(a) vx and vR
(b) nx and nR, compare with each other?

Explaination: (a) vx = vR (b) nx > nR

82. In which directions do the electric and magnetic field vectors oscillate in an electromagnetic wave propagating along the x-axis? [AI 2017]

Explaination: y-axis and z-axis respectively.

83. Which of the following, if any, can act as a source of electromagnetic waves?
(i) A charge moving with a constant velocity.
(ii) A charge moving in a circular orbit.
(iii) A charge at rest. [DoE]

Explaination: (ii) A charge moving in a circular orbit

84. What is the phase difference between electric and magnetic field vectors in an em wave? [DoE]

Explaination: Zero

85. What feature of electromagnetic waves led Maxwell to conclude that light itself is an electromagnetic wave?

Explaination:
The feature of electromagnetic waves is the emergence of the speed of light from purely electromagnetic consideration which led Maxwell to conclude that light itself is an electromagnetic wave.

86. What evidence is there that sound is not electromagnetic in nature?

Explaination:
Sound wave requires an inertial medium for their propagation which shows that sound is not electromagnetic in nature.

87. Do electromagnetic waves carry energy and momentum? [Dehradun-2019] [AI 2017]

Explaination:
Yes. For example, the tail of the comet always stays away from the sun due to the radiation pressure exerted on the tail by the light.

88. Why is the velocity of all types of electromagnetic waves same in free space?

Explaination:
The speed of em wave in free space is given by $$c=\frac{1}{\sqrt{\mu_{0} \varepsilon_{0}}}$$. The value of c is same for all types of em waves because the constants μ0 and ε0 do not depend on the frequency or wavelength of the em waves. They only depend on the medium.

89. How is the speed of em-waves in vacuum determined by the electric and magnetic fields? [Delhi 2017]

Explaination: The speed v of e-m waves in vacuum is determined by the relation|

90. What is the main difference between characteristic X-rays and γ-rays?

Explaination:
Characteristic X-rays are emitted when an orbital electron jumps from a higher energy level to a lower energy level in the atom of high mass number, whereas γ-rays are emitted by radioactive nuclei.

91. Out of microwaves, ultraviolet rays and infrared rays, which radiation will be most effective for emission of electrons from a metallic surface?