A sinusoidal wave y1=a sin (ωt−kx) is reflected from a rigid support and the reflected wave superpose with the incident wave y1. Assume the rigid support to be at x = 0.

On reflection from a rigid support the reflected wave suffers an additional phase change of π. When this reflected wave superimposes with incident wave stationary waves are obtained with node at the rigid support .For a stationary wave ,amplitude of oscillation of particles varies with position of the particles .Since intensity is directly proportional to the square of amplitude , intensity of such stationary waves vary periodically with distance.