Electromagnetic Waves Questions

Multiple Choice Questions

Question 1
What is the frequency range of microwaves?
(a) $10^9$ Hz to $10^{12}$ Hz
(b) $10^{14}$ Hz to $10^{16}$ Hz
(c) $10^{4}$ Hz to $10^{6}$ Hz
(d) $10^{2}$ Hz to $10^{4}$ Hz

Question 2
If E and B represent electric and magnetic field vectors of the electromagnetic wave, the direction of propagation of electromagnetic wave is along
(a) E.
(b) B.
(c) B X E.
(d) E X B.

Question 3
A charged particle oscillates about its mean equilibrium position with a frequency of $10^9$ Hz. The electromagnetic waves produced
(a) will have frequency of $10^9$ Hz.
(b) will have frequency of $2 \times 10^9$ Hz.
(c) will have a wavelength of 0.3 m.
(d) fall in the region of radiowaves

Question 4
The correct ascending order for the frequencies of below electromagnetic radiation is
(a) Gamma Rays ,X-rays,Microwave, Radiowave
(b) Gamma Rays ,Microwave,X-rays, Radiowave
(c) Gamma Rays, Radiowave , Microwave,X-rays,
(d) Radiowave , Microwave,X-rays, Gamma Rays

Question 5
Speed of E.M wave is free space is given
(A) $c=\frac {1}{\sqrt {\mu _0 \epsilon _0}}$
(B) $c=\frac {\sqrt {\epsilon _0}}{\sqrt {\mu _0 }}$
(C) $c=\frac {\sqrt { \mu _0}}{\sqrt {\epsilon _0 }}$
(D) $c=\frac {1}{\mu _0 \epsilon _0}$

Question 6
which of these electromagnetic spectrum does the wavelength $10^{-10}$ m correspond to?
(a)Gamma Rays
(c) Radio wave
(d) Microwave

Question 7
A plane electromagnetic wave propagating along x direction can have the following pairs of E and B
(a) $E_x$, $B_y$
(b) $E_y$, $B_z$
(c) $B_x$, $E_y$
(d) $E_z$, $B_y$

Question 8
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 an electric field.

Question 9
Match the column
(a) a -> s, b -> r , c -> p,d -> q.
(b) a -> s, b -> r , c -> q,d -> p.
(c) a -> r, b -> s , c -> p,d -> q.
(d) a -> p, b -> q , c -> s,d -> r

Question 10

(a) a -> p, b -> r , c -> s,d -> q.
(b) a -> q, b -> r , c -> s,d -> p.
(c) a -> r, b -> p , c -> s,d -> q.
(d) a -> p, b -> q , c -> s,d -> r

Question 11
Propagation constant of the E.M wave is given by
(a) $\frac {2 \pi}{\omega}$
(b) $\frac {c}{\omega}$
(c) $\frac {2 \pi}{c}$
(d) $\frac {\omega}{c}$

Question 12

(a) a -> p, b -> r , c -> s,d -> q.
(b) a -> s, b -> r , c -> p,d -> q.
(c) a -> r, b -> p , c -> s,d -> q.
(d) a -> p, b -> q , c -> s,d -> r

Question 13
A linearly polarized electromagnetic wave given as $\vec{E}=E_0 \cos (kz - \omega t)\vec{i}$ 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
(a) $\vec{E_r}=E_0 \cos (kz + \omega t)\vec{i}$
(b) $\vec{E_r}=-E_0 \cos (kz + \omega t)\vec{i}$
(c) $\vec{E_r}=-E_0 \cos (kz - \omega t)\vec{i}$
(d) $\vec{E_r}=E_0 \sin (kz - \omega t)\vec{i}$

Question 14
The ratio between amplitude of magnetic field and electric field of a E.M wave in free space is given by ?
(a) $1 : c$
(b) $c : 1$
(c) $c^2 : 1$
(d) $1 : c^2$

Question 15
Name the part of the electromagnetic spectrum which is used in green house to keep plants warm
(a) X rays.
(b) UV rays.
(c) infrared.
(d) Micro-wave.

Question 16

(a) a -> q, b -> r , c -> s,d -> p.
(b) a -> s, b -> r , c -> p,d -> q.
(c) a -> r, b -> p , c -> s,d -> q.
(d) a -> p, b -> q , c -> s,d -> r

Question 17
Which of the following electromagnetic rays has maximum wavelength
(a) UV rays
(b) Infrared rays
(c) X -rays
(d) Radio waves

Question 18
A plane E.M wave of frequency 30MHz travels in the free space along x-direction.The electric field component of the wave at a particular point in space and time is E= 6 V/m along y -direction.Its magnetic field component B at this point would be
(a) $2 \times 10^{-8}$ T along y-direction
(b) $6 \times 10^{-8}$ T along y-direction
(c) $6 \times 10^{-8}$ T along z-direction
(d) $2 \times 10^{-8}$ T along z-direction

Question 19
Dimension of $\frac {1}{\mu _0 \epsilon _0}$ where symbols have their usual meaning is
(a) $[L^2T^{-2}]$
(b) $[L^2T^{2}]$
(c) $[L^{-1}T]$
(d) $[LT^{-1}]$

Question 20
The pressure exerted by an electromagnetic wave of intensity I (Wm-2) on a non-reflecting surface os (c is the velocity of light)
(a) $Ic$
(b) $Ic^2$
(c) $\frac {I}{c^2}$
(d) $\frac {I}{c}$

Text Based Questions(long)

Question 1
How is the electromagnetic wave produced?. Draw a sketch of a plane E.M wave propagting along X-axis depicting the direction of oscillating electric and magentic fields

Question 2
Identify the E.M waves whose wavelength lie in the range (a) $10^{-11} \; m < \lambda < 10^{-4} \; m$
(b) $10^{-4} \; m < \lambda < 10^{-6} \; m$
(c) $10^{-12} \; m < \lambda < 10^{-8} \; m$
(d)$10^{-3} \; m < \lambda < 10^{-1} \; m$
Write one use of each of those

Question 3
How does Ampere-Maxwell law explain the flow of current through a capacitor, when it is being charged by a battery? Write the expression for the displacement current in terms of the rate of change of electric flux .

Question 4
Write Maxwell's generalization of Ampere's Circuital Law?

Question 5
Name the parts of the electromagnetic spectrum which is
(a) suitable for radar systems used in aircraft navigation
(b) used to treat muscular strain
(c) used as a diagnostic tool in medicine
Write in brief, how these waves can be produced

Short Answer type

Question 1
For a plane electromagnetic wave, propagating along the z-axis, write the two possible pair of its oscillating electric and magnetic fields. How are the peak values of these (oscillating) fields related to each other?

Question 2
Answer the following
(a) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now ? Explain.
(b) An EM wave exerts pressure on the surface on which it is incident. Justify..?

Question 3
What is displacement current? why was this concept introduced?
Question 4
Write an expression fotr the momentum carrried by an E.M wave?

Question 5
What is green house effect?
Question 6
Electromagnetic waves with wavelength
(i) $\lambda _1$ is used in satellite communication.
(ii) $\lambda _2$ is used to kill germs in water purifies.
(iii) $\lambda _3$ is used to detect leakage of oil in underground pipelines.
(iv)$\lambda _4$ is used to improve visibility in runways during fog and mist conditions.
(a) Identify and name the part of electromagnetic spectrum to which these radiations belong.
(b) Arrange these wavelengths in ascending order of their magnitude.
(c) Write one more application of each

Numerical Questions

Question 1
The oscillating electric field of an electromagnetic wave is given by
$E_Y = 30 \sin (2 \times 10^{11} t + 300 \pi x)$ V/m
(i) Find the direction of propagation of wave
(ii)Find the wavelength of the wave
(iii) write down the expression for magnetic field?

Question 2
A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, $\vec{E}=6 \vec{j}$ V/m. What is B at this point?

Question 3
An electromagnetic wave is travelling in medium with velocity $v=v\vec{i}$ the electric field oscillations of this wave are along y axis
(i) identify the direction in which the magnetic field oscillations are taking place in the e.m. wave
(ii) how are magnitude of elctric and magnetic fields in the electromagnetic wave related to each other?

Question 4
A capacitor, made of two parallel plates each of plate area A and separation d, is being charged by an external ac source. Show that the displacement current inside the capacitor is the same as the current charging the capacitor.

Question 5
In a plane E.M wave ,the electric field oscillates sinusoidally at a frequency of $2 \times 10^{10}$ Hz and amplitude 48 V/m
(a) what is the wavelength of a wave?
(b) What is the amplitude of the oscillating magnetic field
(c) show that averge energy density of the $\vec{E}$ field equals the average energy density of the $\vec{B}$ field

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