Question

Three sources of sound $S_1,S_2$ and $S_3$ of equal intensity are placed in a straight line with $S_1,S_2=S_2,S_3$ (figure 16-E5). At a point P, far away from the sources, the wave coming from $S_2$ is ${120}^{\circ }$ ahead in phase of that from $S_1$ Also, the wave coming from $S_3$ is ${120}^{\circ }$ ahead of that from $S_2$. What would be the resultant intensity of sound at P?

Answer 1

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.