Two speakers connected to the same source of fixed frequency are placed 2.0m apart in a box. A sensitive microphone placed at a distance of 4.0 m from their midpoint along the perpendicular bisector shows maximum response. The box is slowly rotated until the speakers are in line with the microphone. The distance between the midpoint of the speakers and the microphone remains unchanged. Exactly five maximum responses are observed in the microphone in doing this. the wavelength of the sound wave is

Explanation

The initial and final positions of speakers ` S_(1) and S_(2)` and microphone `M` are shown in Figs. S7.2 (a) and (b). Intially the path difference from `S_(1) to M and S_(2) to M` is zero .
I.e. `S_(2) M - S_(1) M = 0`
Finally the path difference
`Delta = S_(2)P - S_(1)P = 5 - 3 = 2 m`
For `n th "maxima" Delta = n lambda`
` 2 = 5 lambda or lambda = 2//5 = 0.4 m`