Question

A plane electromagnetic wave travels in free space along the x-direction. The electric field component of the wave at a particular point of space and time is $E = 6 \; V \; m^{-1}$ along y-direction. Its corresponding magnetic field component, B would be :

• A. $6 \times 10^{-8}$ T along z-direction
• B. $6 \times 10^{-8}$ T along x-direction
• C. $2 \times 10^{-8}$ T along z-direction
• D. $2 \times 10^{-8}$ T along y-direction

Answer 1

Answer: (C)

$2 \times 10^{-8}$ T along z-direction

Answer 2

The direction of propogation of an EM wave is direction of $\vec{E} \times \vec{B}$ .
$\hat{i} = \hat{j} \times \hat{B}$
$\Rightarrow \; \hat{B} = \hat{k}$
$C = \frac{E}{B} \; \Rightarrow B = \frac{E}{C} = \frac{6}{3 \times 10^{8}}$
$B = 2 \times 10^{-8} T$ along $z$ direction.