Constructive Interference Maximizes Sound Intensity

Steps:

• Waves from two coherent sources interfere; constructive interference occurs when path lengths differ by integer multiples of wavelength (Δd = mλ).
• Examine diagram: wavefronts show equidistant paths to point D, yielding Δd = 0 (m=0).
• At D, waves arrive in phase, amplitudes add to double intensity.
• Other points have non-zero Δd not equal to mλ, reducing intensity.

Why D is correct:

• D lies on the perpendicular bisector; path difference is zero, so waves constructively interfere per superposition principle, producing maximum amplitude (4x intensity of one source).

Why the others are wrong:

• A: Path difference ≈ λ/2, causing destructive interference and minimum sound.
• B: Unequal paths yield partial interference, not full constructive.
• C: Off-axis position results in phase mismatch, lowering intensity.

Final answer: D