Three sources of sound `S_1, S_2 and S_3` of equal intensity are placed in a straight line with `S_1S_2=S_2=S_3`. At a point P. far away from the sources, the wave coming from `S_2 si 120^@` ahead in phase of that from `S_1`. Also, the wave coming from `S_3` is `120^@` ahead of that from `S_2`. What would be the resultant intensity of sound at `P`?

Explanation

Because the 3 sources have equal intensity, amplitude are equal
So, `A_1=A_2=A_3`
amplitude of the resultant =0
`(vector method)
So the resultant intensity at B is zero.