Two coherent sinusoidal waves of intensities I₁ and I₂ superpose at a point with phase difference φ. Which expression gives the resultant intensity?
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Question

Two coherent sinusoidal waves of intensities I₁ and I₂ superpose at a point with phase difference φ. Which expression gives the resultant intensity?

G1 Physics · Accepted Answer

If the displacement amplitudes are a₁ and a₂, the resultant amplitude satisfies a² = a₁²+a₂²+2a₁a₂ cosφ. Because intensity is proportional to amplitude squared, I = I₁+I₂+2√(I₁I₂) cosφ. Correct option: B.