Question

An electromagnetic wave of frequency $45 \,MHz$ travels in free space along $X$ -axis. At some point and at some instant, the electric field has a maximum value of $750\, NC ^{-1}$ 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
$B =\frac{F}{c}$
$E =750 \,N / C$
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 $