# MCQ Physics - Topic Electromagnetic Wave

Que 1
The dimensional formula of
1/(magnetic permeability×electric permittivity)

a) [LT^-1]

b) [L^-1T]

c) [L^2T^-2]

d) [TL]

Ans (c)

Que 2

The electromagnetic wave which has least wavelength

b) X rays

c) microwaves

d) Gamma waves

Ans (d)

Que 3

The electromagnetic wave which has longest wavelength

b) X rays

c) microwaves

d) Gamma waves

Ans (a)

Que 4

Electric and magnetic field in an electromagnetic wave are

a) mutually perpendicular and in same phase

b) mutually perpendicular and in opposite phase

c) parallel to each other and same phase

d) parallel to each other and in opposite phase

Ans (a )

Que 5

Find the energy of photon of electromagnetic radiation of wavelength 200 A°

a) 1.76×10^-18 J

b) 0.99×10^-18 J

c) 1.76

d) 0.99

Ans (b)

Hint

Formula used

E=hc/wavelength(lambda)

Que 6

Find the speed of light in air if an electromagnetic wave is travelling in air whose dielectric constant is k = 1.006

a) 3×10^8 m/s

b) 3.88 ×10^8 m/s

c) 2.5×10^8 m/s

d) 4.6×10^8 m/s

Ans (a)

Hint
Formula used

v=c/√k
Que 7

Calculate the wavelength of a radio wave of frequency 1 MHz

a) 400m

b) 300 m

c) 350 m

d) 200 m

Ans (b)

Formula used

Velocity =frequency×wavelength

Que 8

An electromagnetic wave with pointing vector 5W/m^2 is absorbed by the surface of some area if the force on the surface is 10^-7 N find the area

a) 6 m^2

b) 3 m^2

c) 60m^2

d) 4 m^2

Ans (a)

Hint

P=I/c= 5/(3×10^8)

F = P×A

Que 9

The rays produced in sonography are

a) microwave

b) infrared

c) sound waves

d) ultrasound

Ans (d )

Que 10

Find the average power per unit area at a distance of 2 m from a small bulb if the bulb emits 20 watt of electromagnetic radiation uniformly in all directions

a) 0.69 W/m^2

b) 0.56 W/m^2

c) 0.78 W/m^2

d) 0.39 W/m^2

Ans (d )

Hint

I=P/(4πr^2)

Fri Nov 18, 2022