Question

A plane EM wave of frequency 25 MHz travels in free space along the +x direction. At a particular point in space and time,$\overrightarrow{E}=6.3\hat{j}V/m$ . What is $\overrightarrow{B}$ at this point?

• A. $2.52\times {10}^{-5}\hat{k}T$
• B. $2.52\times {10}^{-5}(-\hat{k})T$
  
• C. $2.1\times {10}^{-8}\hat{k}T$
• D. $2.1\times {10}^{-8}(-\hat{k}T$

Answer 1

The correct option is C $2.1\times {10}^{-8}\hat{k}T$

$B=\frac{E}{c}=\frac{6.3}{3\times {10}^8}=2.1\times {10}^{-8}T$
For direction of $\overrightarrow{B}$
$\hat{E}\times \hat{B}=\hat{i}\therefore \hat{B}=\hat{k}$