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(C) The electric field of an electromagnetic wave is given by $E = E_0 \sin(\omega t - kx)$.The energy density $u$ is proportional to the square of th

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double the frequency of the wave

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(C) The electric field of an electromagnetic wave is given by $E = E_0 \sin(\omega t - kx)$.The energy density $u$ is proportional to the square of the electric field,$u \propto E^2$.Thus,$u \propto \sin^2(\omega t - kx)$.Using the trigonometric identity $\sin^2 	heta = \frac{1 - \cos(2	heta)}{2}$,we get $u \propto \frac{1 - \cos(2(\omega t - kx))}{2}$.The frequency of the oscillation of the energy density is determined by the term $2\omega t$.Since the angular frequency of the wave is $\omega = 2\pi f$,the angular frequency of the energy oscillation is $2\omega = 2(2\pi f) = 2\pi(2f)$.Therefore,the frequency of the energy oscillation is $2f$,which is double the frequency of the wave.

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

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