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

Options

A. double the frquency of the wave
B. zero frequency
C. the frequency of the wave
D. half the frequency of the wave.

Answer

a

Explanation

Energy contained per unit volume through which
em wave is propagating is sum of
energy of electric field and energy of magnetic
field i.e., `u=u_E_u_B=1/2in_0E^2+1/2(B^2)/(mu_0)`
where E and B are sinusoidal function
i.e., `E=E_0sin omega(t-x/c)`
`B=B_0sin omega(t-x/c)`
`u_E=1/2in_0E^2=1/2in_0E_0^2 sin^2 omega(t-x/c)`
`=1/(2in_0) E_0^2 [1-cos 2 omega(t-x/c)]`
the frequency of `u_E` is double than that of
em wave. Similarly, the frequency
of `u_B` is double than that of em wave.