Question

The energy contained in a small volume through which an electromagnetic wave is passing oscillates with

• A. Zero frequency
• B. The frequency of the wave
• C. Half the frequency of the wave
• D. Double the frequency of the wave

Answer 1

The correct option is D Double the frequency of the wave

The energy per unit volume contained in electromagnetic wave is

$U=\frac{1}{2}ϵE^2+\frac{B^2}{2\mu }$

If electric field is represented by $E_0\cos (\omega t-Kx)$, the energy equation will contain term ${\cos }^2(\omega t-Kx)$ and hence the frequency of oscillations will be double that of wave.