Question

Two coherent narrow source emitting sound of wavelength λ in the same phase are placed parallel to each other at a small separation of 2λ. The sound is detected by moving a detector on the screen ∑ at a distance D (>> λ) from the source S₁ as shown in Fig. Find the distance x such that the intensity at P is equal to the intensity at O.

Answer 1

The maximum path difference between the sounds can be 2λ, and minimum can be zero, when x tends to infinity. So there is only one position between them at which intensity is maximum, for which path difference between sound at P is λ.