Read the passage and answer the question.

A wave is represent by variable Y which gives the displacement of the particles of the medium in which the wave is travelling at any given instant of time. In the same context, consider two waves y1 and y2 which superpose such that y gives the resultant of the two waves. By resultant of the two waves, we mean, that y gives the vector sum of the displacements of each of the individual wave.

For constructive interference, what should be the phase difference should ?

2nπ, n = 0, 1,2,....

Cos Φ = + 1

∴ Φ = 2nπ, n = 0, 1,2,....