Question

Which of the following have zero average value in a plane electromagnetic wave?

• A. Electric energy
• B. Magnetic energy
• C. Electric field
• D. Both magnetic and electric field

Answer 1

The correct option is D

Both magnetic and electric field

1. The electric and magnetic fields fluctuate sinusoidally in a planar electromagnetic wave. The electric and magnetic fields of an electromagnetic wave traveling in the z-direction are given by: $\begin{array}{r}{\mathrm{E}}_{\mathrm{x}}={\mathrm{E}}_0\sin (\mathrm{kz}-\mathrm{\omega t})\\ {\mathrm{B}}_{\mathrm{y}}={\mathrm{B}}_0\sin (\mathrm{kz}-\mathrm{\omega t})\end{array}$
2. These are functions that have a sinusoidal shape. As a result, the average value of the electric and magnetic fields is zero for a fixed value of $\mathrm{z}$.

Hence, the correct answer is Option (D).