Q: The rms value of the electric field of the light coming from the Sun is 720 N/C. The average total energy density of the electromagnetic wave is
(a) 6.37 × 10-9 J/m3
(b) 81.35 × 10-12 J/m3
(c) 3.3 × 10-3 J/m3
(d) 4.58 × 10-6 J/m3
Ans: (d)
Sol: Erms = 720 N/C
$ \displaystyle u = \frac{1}{2} \epsilon_0 E_0^2$