Question

A plane Electromagnetic wave of frequency $25MHz$ travels in free space along the $+x$ direction. At a particular point in space and time, $\overrightarrow{E}=63\hat{j}V/m$. 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

$2.1\times {10}^{-8}\hat{k}T$

Relation betweeen magnetic and electric fields in a electro magnetic wave is $B=\frac{E}{c}=\frac{6.3}{3\times {10}^8}$

$=2.1\times {10}^{-8}T$

For direction of $\overrightarrow{B}$
As wave is propagating alon $+x$ axis

$\hat{E}\times \hat{B}=\hat{i}$

$\therefore \hat{B}=\hat{k}$