Constructive interference

When two waves meet which are in phase, their amplitudes add together to create a wave with a larger amplitude. That’s called constructive interference.

If the phase difference between the two waves is zero or a multiple of 360°, the waves are in phase. That means that the peaks of one wave line up exactly with the peaks of the other wave, and the troughs line up exactly with the troughs. When this happens, the amplitudes of the two waves add together to create a new wave with a larger amplitude.

For example, if two waves each have an amplitude of 2 units, when they interfere, they will interfere constructively to create a new wave with an amplitude of 4 units.