# MCQ Questions for Class 12 Physics Chapter 8 Electromagnetic Waves with Answers

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## Electromagnetic Waves Class 12 MCQs Questions with Answers

Solve this Electromagnetic Waves Multiple Choice Questions of Class 12 Physics Chapter 8 MCQ, so as not to miss out on any concept from being clear about what they mean!

Question 1.
If $$\vec {E}$$ and $$\vec {B}$$ represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along
(a) $$\vec {E}$$
(b) $$\vec {B}$$
(c) $$\vec {B}$$ × $$\vec {E}$$
(d) $$\vec {E}$$ × $$\vec {B}$$

Answer: (d) $$\vec {E}$$ × $$\vec {B}$$

Question 2.
The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is
(a) c : 1
(b) c² : 1
(c) 1 : 1
(d) √c : 1

Question 3.
A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The electromagnetic waves produced will not
(a) have a frequency of 109 Hz.
(b) have a frequency of 2 × 109 Hz.
(c) have a wavelength of 0.3 m.
(d) fall in the region of radio waves.

Answer: (b) have a frequency of 2 × 109 Hz.

Question 4.
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) none of these.

Answer: (b) moving in a circular orbit.

Question 5.
A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, the electric vector is $$\vec {E}$$ = 6.3 Vm-1$$\hat {j}$$. Calculate $$\vec {B}$$ at
this point.
(a) 2.1 × 10-8 T
(b) 1.2 × 10-8 T
(c) 1.9 × 10-8 T
(d) 0.21 × 10-8T

Answer: (a) 2.1 × 10-8 T

Question 6.
What physical quantity is the same for X-rays of wavelength 10-10 m, red light of wavelength 680 nm and radio waves of wavelength 500 m?
(a) Wavelength
(b) Frequency
(c) Speed
(d) None of these.

Question 7.
In an electromagnetic wave in free space, the root mean square value of the electric field is Erms = 6 V m-1. The peak value of the magnetic field is:
(a) 2.83 × 10-8 T
(b) 0.70 × 10-8 T
(c) 4.23 × 10-8 T
(d) 1.41 × 10-8 T

Answer: (a) 2.83 × 10-8 T

Question 8.
Arrange the following electromagnetic radiations per quantum in the order of increasing energy:
(A) Blue light
(B) Yellow light
(C) X-ray
(a) A, B, C, D
(b) C, A, B, D
(c) B, A, D, C
(d) D, B, A, C

Answer: (d) D, B, A, C

Question 9.
A radiation of energy ‘E’ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (c = Velocity of light)
(a) 2E/c
(b) 2E/c²
(c) E/c²
(d) E/c

Question 10.
Match List -I (Electromagnetic wave type) with List – II (Its association/application) and select the correct option from the choices given below the lists:

 List I List II (A) Infrared (i) To treat muscular strain (B) Radio waves (ii) For broadcasting (C) X-rays (iii) To detect fracture in bones (D) Ultraviolet rays (iv) Absorbed by the ozone layer of the atmosphere

(a) A-iii, B-ii, C-i, D-iv
(b) A-i, B-ii, C-iii, D-iv
(c) A-iv, B-iii, C-ii, D-i
(d) A-i, B-ii, C-iv, D-iii

Answer: (b) A-i, B-ii, C-iii, D-iv

II. Fill in the blanks

Question 1.
The conduction current is same as …………………. whether the source is ac or dc.

Question 2.
The current that flows inside a capacitor is ………………. current.

Question 3.
An oscillating charge particle radiates ……………….

Question 4.
EM waves are …………….. in nature.

Question 5.
EM waves travel with a speed …………………

Answer: 3 × 108 m s-1

Question 6.
Human body radiates ………………… of EM spectrum.

Question 7.
EM waves transport both ………………… and ………………..

Question 8.
EM waves are produced by ………………… charsed particles.

Question 9.
In terms of permittivity (ε0) of free space and permeability (µ0) of free space the velocity of EM wave is ………………..

Answer: c = $$\frac { 1 }{\sqrt{µ_0ε_0}}$$

Question 10.
The ratio of velocities of light waves of wavelengths 400 nm and 800 nm in vacuum is ………………..

Question 11.
For an EM wave the electric field along the X-axis is given by Ex = E0 sin (kz – ωt) then magnetic field is given by ……………….

Answer: By = B0 sin (kz – ωt)

Question 12.
The maximum value of electric field (E0) and maximum value of magnetic field (B0) in EM wave are related as ………………

Question 13.
The energy of EM wave is divided …………….. amongst the electric and the magnetic field.

Question 14.
Shorter the wavelength of an electromagnetic wave ………………….. energy it carries.

Question 15.
The orderly distribution of electromagnetic radiations according to their frequency or wavelength is termed as ……………….. spectrum.

Question 16.
………………. are used as a diagnostic tool.

Question 17.
For Sterilisation ……………….. rays are used.

Question 18.
For looking through haze ………………… are used.

Question 19.
………………. are used for cooking.

Question 20.
Waves used to transmit cellular telephone message are ………………..

Question 21.
To study structure of crystals ……………….. are used.

Question 22.
Human eye can detect ……………….. part of electromagnetic spectrum.

Question 23.
To treat cancer and tumour in radiography ………………… rays are used.

Question 24.
During the propagation of an EM wave in a medium electrical energy density is ………………….. to magnetic energy density.