The average intensity of a plane electromagnetic wave in vacuum is 12 W/m². If its average total electromagnetic energy density is N×10⁻⁸ J/m³, find N. Take c = 3×10⁸ m/s.

Question

G1 Physics · Accepted Answer

For a plane electromagnetic wave, I = c⟨u⟩, where ⟨u⟩ is the average total electromagnetic energy density. Therefore, ⟨u⟩ = I/c = 12/(3×10⁸) = 4×10⁻⁸ J/m³. Hence N = 4.