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

(a) Electric field

(b) Magnetic field

(c) Electric energy

(d) Magnetic energy

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#### Solution

(a) Electric field

(b) Magnetic field

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:

E_{x} = E_{0} sin (kz – ωt)

B_{y} = B_{0} sin (kz – ωt)

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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