If the electric-field amplitude of a plane electromagnetic wave is doubled without changing the medium, its average intensity becomes:
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Question

If the electric-field amplitude of a plane electromagnetic wave is doubled without changing the medium, its average intensity becomes:

G1 Physics · Accepted Answer

Average intensity of a plane wave is proportional to the square of the electric-field amplitude: I ∝ E₀². If E₀' = 2E₀, then I'/I = (2E₀)²/E₀² = 4. Thus the new intensity is 4I. Correct option: B.