Two coherent sound waves have intensities I₁ and I₂ at a point and a phase difference φ. Which expression gives the resultant intensity?
Options

Question

Two coherent sound waves have intensities I₁ and I₂ at a point and a phase difference φ. Which expression gives the resultant intensity?

G1 Physics · Accepted Answer

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