Question

Three sources of sound S₁, S₂ and S₃ of equal intensity are placed in a straight line with S₁S₂ = S₂S₃. 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?

Answer 1

Given:
All the three sources of sound, namely, S₁, S₂ and S₃ emit equal intensity of sound waves.
Therefore, all three sources have equal amplitudes.
∴ A₁ = A₂ = A₃
Now, by vector method, the resultant of the amplitudes is 0.
So, the resultant intensity at P is zero.
(a)

(b)