Two sources of sound `S_1 and S_2` vibrate at same frequency and are in phase. The intensity of sound detected at a point P as shown in the figure is `I_0` . (a) If `theta` equals `45^@`, what will be the intensity of sound detected at this point if one of the sources is switched off ? (b) What will be the answer of the previous part if `theta= 60^@` ?

Answer

B, D

Explanation

path difference and hence phase difference at `p` from both the sources is `0^(@)` , whether `theta=45^(@)` , or `theta=60^(@)` . So, both the wave will interfere constructively. Or maximum intersity will be obtained. From
`I_(max)=(sqrt(I_(1))+sqrt(I_(2)))^(2)` we have
`I_(0)=(sqrt(I_(1))+sqrt(I))^(2)=4I(I_(1)=I_(2)+I` , say)
`:. I=I_(0//4)`
When one source is switched off, no interfernce will be obtained. Intensity will be due to a single source or `I_(0//4)` .
(b)At `theta=60^(@)` , also maximum intensity or `I_(0)` will be observed.