The displacement at any time due to any number of waves meeting simultaneously at a point in a medium is the vector sum of the individual displacements due each one of the waves at that point at the same time.

If………. are the displacements at a particular time at a particular position, due to individual waves, then the resultant displacement. 

Examples

(i)    Radio waves from different stations having different frequencies cross the antenna. But our T.V/Radio set can pick up any desired frequency.

(ii)   When two pulses of equal amplitude on a string approach each other [fig. (A)], then on meeting, they superimpose to produce a resultant pulse of zero amplitude [fig (B)]. After crossing, the two pulses travel independently as shown in [fig (C)] as if nothing had happened.

       Important applications of superposition principle :

      (a) Interference of waves           (b) Stationary waves     (c) Beats.