Question

During the propagation of electromagnetic waves in a medium,

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

Answer 1

The correct option is A

Electric energy density is equal to the magnetic energy density.

Here, $u_E=\frac{1}{2}{ϵ}_0{E}^2$ and $u_B=\frac{B^2}{2{\mu }_0}$

Moreover, $E=cB$ and $c=\frac{1}{\sqrt{{\mu }_0{ϵ}_0}}$

Hence, $u_E=\frac{1}{2}{ϵ}_0{E}^2=\frac{1}{2}{ϵ}_0(cB{)}^2=\frac{1}{2}{ϵ}_0\frac{1}{{\mu }_0{ϵ}_0}{B}^2=\frac{B^2}{2{\mu }_0}=u_B$