Question

Which of the following have zero average values 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

Explanation in case of correct option:

In the case of option D.

1. Both electric and magnetic fields have sinusoidal nature in a plane electromagnetic wave.
2. As we know, the average value of a sinusoidal wave is zero,
3. So both magnetic and electric fields have average values of zero.
4. Thus option D is the correct option.

Explanation in case of incorrect options:

In the case of option A.

1. Electrical energy is proportional to the square of the intensity.
2. And hence average value is not zero.
3. Thus option A is an incorrect option.

In the case of option B.

1. Magnetic energy is also proportional to the square of the intensity.
2. And hence average value is not zero.
3. Thus option B is an incorrect option.

In the case of option C.

1. Both electric and magnetic fields have sinusoidal nature in a plane electromagnetic wave.
2. As we know, the average value of a sinusoidal wave is zero,
3. So both magnetic and electric fields have average values of zero.
4. But option C talks about the electric field only. and not about the magnetic field. Whether option D talks about both.
5. Thus option C is an incorrect option.

Thus option D is the correct option.