The electric-field amplitude of an electromagnetic wave becomes three times its initial value while the medium remains unchanged. If the new average intensity is N times the original intensity, find N.

Question

G1 Physics · Accepted Answer

Average intensity is proportional to the square of field amplitude: I ∝ E₀². If E₀' = 3E₀, then I'/I = (3E₀)²/E₀² = 9. Hence N = 9.