JEE Main · 2023 · 10 Apr 2023 · Shift 1 · EM Waves

The energy of an electromagnetic wave contained in a small volume oscillates with

(A)zero frequency
(B)half the frequency of the wave
(C)double the frequency of the wave✓ Correct
(D)the frequency of the wave

Answer: (C)

Solution

The field of the wave varies as

E = E_{0} sin (ω t - k x)

, and the stored energy density is proportional to

E^{2} \propto sin^{2} (ω t - k x) = \frac{1}{2} [1 - cos (2 ω t - 2 k x)]

. The oscillating part carries angular frequency

2 ω

, so the energy oscillates at double the frequency of the wave.

JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Single correct option

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