A flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal plane wave: $E_x = 36sin (1.20 \times 10^7z – 3.6 \times 10^{15}t) V/m$. The average intensity of the beam will be:
Answer & explanation
Correct answer: option 2
$ I = \frac{1}{2} \epsilon_0 cE^2 = \frac{8.85\times 10^{-12} \times 3\times 10^8\times 36^2}{2} = 1.72W/m^2$