A sound sources, detector and a movable wall are arranged as shown in figure. In this arrangement detectir us detacting the maximum intensity. If the speed of sound is `330 m//s` in air and frequency of source is `660 Hz`, then find the minimum distance by which the wall should be moved away from source, so that detector dtects minimmum intensity.

Answer

`12.5 cm`

Explanation

Let `SO + OD - SD = n lambda`…….`I` , constructive interference
`rArr SP + PD - SD = n lambda`……….. `II` , destructive interference
`II - I` gives
`SP - SO + PD - OD = (lambda)/(2)`
`OP + OP = (lambda)/(2)`
`OP = (lambda)/(4) - (v)/(f) = (1)/(4) (330)/(660) = 0.125 m = 12.5 cm`