Question

Three sources of sound S₁, S₂ and S₃ of equal intensity are placed in a straight line with S₁S₂ = S₂S₃, (figure 16-E5). At a point P, far away from the sources, the wave coming from S₂ is 120° ahead in phase of that from S₁. Also, the wave coming from S₃ is 120° ahead of that from S₂. What would be the resultant intensity of sound at P?

Comments

What about the path difference?

Answer 1

Because the 3 sources have equal intensity, amplitude are equal
So, A₁ = A₂ = A₃
As shown in the figure, amplitude of the resultant = 0 (vector method)
So, the resultant, intensity at B is zero.