In an electromagnetic wave, the amplitude of electric field is 1 V/m. The frequency of wave is 5 × 10–14 Hz. The wave is propagating along z-axis. The average energy density of electric field, in Joule/m3, will be:
Answer & explanation
Correct answer: option 2
Average energy density is given by
$U_{E}=\frac{1}{2} \varepsilon_0 E^2=\frac{1}{2} \varepsilon_0\left(\frac{E_0}{\sqrt{2}}\right)^2=\frac{1}{4} \varepsilon_0 E_0^2$
$=\frac{1}{4} \times 0.85 \times 10^{-12} \times(1)^2$
= 2.2 × 10–12 J/m3