Question

During the propagation of electromagnetic waves in a medium

• A. Electric energy density is equal to the magnetic energy density
• B. Electric energy density is double of the magnetic energy density
• C. Electric energy density is half of the magnetic energy density
• D. Both electric and magnetic energy densities are zero.

Answer 1

The correct option is A Electric energy density is equal to the magnetic energy density

Electric energy density is equal to the magnetic energy density.
Here, $U_E=\frac{1}{2}{ϵ}_o{E}^2.....\left(1\right)$
and $U_B=\frac{B^2}{2{\mu }_o}.....\left(2\right)$

Moreover, $E=cB$ and $c=\frac{1}{\sqrt{{\mu }_o{ϵ}_o}}$

In equation 1,

$U_E=\frac{1}{2}{ϵ}_o(cB{)}^2{U}_E=\frac{1}{2}{ϵ}_o(\frac{1}{\sqrt{{\mu }_o{ϵ}_o}}B{)}^2{U}_E=\frac{B^2}{2{\mu }_o}=U_B$

Hence, option $C$ is correct.