A sinusoidal electromagnetic wave in vacuum has peak electric-field amplitude E₀ = 200 V/m. Take ε₀ = 9×10⁻¹² F/m and c = 3×10⁸ m/s. If its average intensity is N W/m², find N.

Question

G1 Physics · Accepted Answer

Average intensity is I = ½cε₀E₀². Substitute: I = ½(3×10⁸)(9×10⁻¹²)(200²). Since 200² = 4×10⁴, I = ½×3×9×4 = 54 W/m². Hence N = 54.