Question

An EM wave is propagating in a medium with velocity \[\vec{V}=V\hat{i}\] . The instantaneous oscillating electric field of this EM wave is along the \[+y\] axis. Then the direction of the oscillating magnetic field of the EM wave will be along.
A. -Y direction
B. -Z direction
C. -X direction
D. +Z direction

Answer 1

Hint: EM wave is made up of oscillating electric and magnetic fields. The direction of oscillating electric field, magnetic field and direction of propagation are mutually perpendicular to each other. Use the cross product of any two quantities in order to find the direction of the third quantity.

Complete step-by-step answer:
Electromagnetic waves consist of oscillating electric and magnetic fields. Both fields oscillate in a perpendicular direction and they are also perpendicular to direction of propagation of the wave.
Given that \[\vec{V}=V\hat{i}\] ,
Therefore the wave propagates along the positive direction of the x axis.
Also we have electric fields oscillating along the \[+y\] axis.
Hence,
 \[\text{The direction of magnetic field = direction of propagation }\!\!~\!\!\text{ }\!\!\times\!\!\text{ direction of electric field}\]
 \[\text{The direction of magnetic field }=\hat{i} \times \hat{j}\]
 \[\text{The direction of magnetic field }=\hat{k}\]
Therefore, the direction of the oscillating magnetic field of the EM wave will be along \[+z\] direction.
Answer- D.

Additional Information:
Electromagnetic waves travel with the speed of $ 3\times {{10}^{8}}m/s $ . These are transverse in nature. These electromagnetic waves show many phenomena like interference, diffraction, polarization etc. EM waves carry momentum, energy and angular momentum. An accelerating charge particle emits EM waves. The light coming from the Sun, the heat produced by burning wood and microwaves in the oven are the form of electromagnetic waves.

Note: Electromagnetic waves do not require any medium to propagate. The oscillating electric field produces a varying magnetic field and this oscillating magnetic field again produces a circulating electric field. In this way the electromagnetic wave is self-sustaining.