Question
Which of the following have zero average value in a plane electromagnetic wave?
- Electric field.
- Magnetic field.
- Electric energy.
- Magnetic energy.
✓
Answer
- Electric field.
- Magnetic field.
Explanation:
In a plane electromagnetic wave, the electric and the magnetic fields oscillate sinusoidally. For an electromagnetic wave propagating in the z-direction, the electric and magnetic fields are given by,
$\text{E}_\text{x}=\text{E}_0\sin(\text{kz}-\omega\text{t})$
$\text{B}_\text{y}=\text{B}_0\sin(\text{kz}-\omega\text{t})$
These are sinusoidal functions. Therefore, for a fixed value of z. the average value of the electric and magnetic fields are zero.
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