Question

An electromagnetic wave of frequency $45MHz$ travels in free space along $X$ -axis. At some point and at some instant, the electric field has a maximum value of $750N{C}^{-1}$ along $Y$ -axis. The magnetic field at this position and time is

• A. $2.5\times 10^{-6}\hat{j}$
• B. $5\times 10^{-6}\hat{k}T$
• C. $2.5\times 10^{-6}\hat{k}T$
• D. $2.5\times 10^{-6}\hat{i}T$

Answer 1

Answer: (C)

Relation between electric and magnetic field in electromagnetic wave
$B=\frac{F}{c}$
$E=750N/C$
Speed of light,
$c=3\times 10^{8}m/s$
$B=\frac{750}{3\times 10^8}$
$B=2.5\times 10^{-6}T$
As, $B$ must be perpendicular to both $c$ and $E$ i.e.it is along $Z$ -axis.
$B=2.5\times 10^{-6}\hat{k}T$