Question

A wave having an amplitude of 3cm is to be superimposed with another wave of the same amplitude. What should be their phase difference if the net amplitude has to be 0?

(a) π/2

(b) π

(c) 2π

(d) 0

This question was posed to me in quiz.

This intriguing question comes from Principle of Superposition of Waves topic in section Waves of Physics – Class 11

Answer 1

The correct answer is (b) π

Explanation: The net amplitude is given by: A^2 = A1^2 + A2^2 + 2A1A2cosθ,

where θ is the phase difference.       

For A to be zero 9 + 9 + 2(9)(9)cosθ = 0   

∴ θ = π.