Q 21 :

A plane electromagnetic wave of frequency 20 MHz propagates in free space along $x$-direction. At a particular space and time, $\overrightarrow{E}=6.6\hat{j}\text{ V/m}$. What is $\overrightarrow{B}$ at this point?              [2023]

• $-2.2\times {10}^{-8}\hat{i}\text{ T}$

   

• $2.2\times {10}^{-8}\hat{k}\text{ T}$

   

• $-2.2\times {10}^{-8}\hat{k}\text{ T}$

   

• $2.2\times {10}^{-8}\hat{i}\text{ T}$

   

Q 22 :

Which of the following Maxwell’s equations is valid for time varying conditions but not valid for static conditions?                   [2023]

• $\oint \overrightarrow{B}·\overrightarrow{d\mathcal{l}}={\mu }_{0}I$

   

• $\oint \overrightarrow{E}·\overrightarrow{d\mathcal{l}}=0$

   

• $\oint \overrightarrow{E}·\overrightarrow{d\mathcal{l}}=-\frac{\partial {\varphi }_B}{\partial t}$

   

• $\oint \overrightarrow{D}·\overrightarrow{dA}=Q$

   

Q 23 :

The source of time varying magnetic field may be                     [2023]

(A) a permanent magnet
(B) an electric field changing linearly with time
(C) direct current
(D) a decelerating charge particle
(E) an antenna fed with a digital signal

Choose the correct answer from the options given below:

• (D) only

   

• (C) and (E) only

   

• (A) only

   

• (B) and (D) only

   

Q 24 :

In an electromagnetic wave, at an instant and at a particular position, the electric field is along the negative $z$-axis and magnetic field is along the positive $x$-axis. Then the direction of propagation of electromagnetic wave is           [2023]

• at 45° angle from positive y-axis

   

• negative y-axis

   

• positive z-axis

   

• positive y-axis

   

Q 25 :

To radiate EM signal of wavelength $\lambda$ with high efficiency, the antennas should have a minimum size equal to            [2023]

• $\frac{\lambda }{2}$

   

• $\frac{\lambda }{4}$

   

• $2\lambda$

   

• $\lambda$

   

Q 26 :

In a medium the speed of light wave decreases to 0.2 times to its speed in free space. The ratio of relative permittivity to the refractive index of the medium is $x:1$. The value of $x$ is _______. (Given speed of light in free space $=3\times {10}^8{\text{ ms}}^{-1}$ and for the given medium ${\mu }_r=1$)            [2023]

Q 27 :

Match List – I with List – II.                              [2026]

	List – I		List – II
	(Relation)		(Law)
A.	$\oint \overrightarrow{E}·d\overrightarrow{l}=-\frac{d}{dt}\oint \overrightarrow{B}·\overrightarrow{da}$	I.	Ampere’s circuital law
B.	$\oint \overrightarrow{B}·\overrightarrow{dl}={\mu }_0(I+{\epsilon }_0\frac{{\displaystyle d{\Phi }_E}}{{\displaystyle dt}})$	II.	Faraday’s laws of electromagnetic induction
C.	$\oint \overrightarrow{E}·\overrightarrow{da}=\frac{1}{{\epsilon }_0}{\int }_V\rho dV$	III.	Ampere–Maxwell law
D.	$\oint \overrightarrow{B}·\overrightarrow{dl}={\mu }_{0}I$	IV.	Gauss’s law of electrostatics

 

Choose the correct answer from the options given below:

• A–II, B–III, C–I, D–IV

   

• A–II, B–III, C–IV, D–I

   

• A–I, B–IV, C–III, D–II

   

• A–IV, B–I, C–II, D–III

   

Q 28 :

The electric field in a plane electromagnetic wave is given by : 

$E_y=69\sin [0.6\times {10}^{3}x-1.8\times {10}^{11}t ]V/m$

The expression for magnetic field associated with this electromagnetic wave is ________ T.       [2026]

• $B_z=2.3\times {10}^{-7}\sin [0.6\times {10}^{3}x-1.8\times {10}^{11}t]$

   

• $B_z=2.3\times {10}^{-7}\sin [0.6\times {10}^{3}x+1.8\times {10}^{11}t]$

   

• $B_y=69\sin [0.6\times {10}^{3}x+1.8\times {10}^{11}t]$

   

• $B_y=2.3\times {10}^{-7}\sin [0.6\times {10}^{3}x-1.8\times {10}^{11}t]$