Destructive Interference & Constructive Interference

Wave interference is when two or more waves interact at the same time and a combined, stronger wave is formed. Destructive interference and constructive interference are two types of wave interference. During any wave interference the shape of the medium is determined by the sum of the separate amplitudes of each wave. i.e. when waves interfere, amplitudes add. 



In destructive interference, the positive amplitude of one crest is added to the negative amplitude of the other trough. The two waves combined interfere with each other, weakening the wave.

In constructive interference, the positive amplitude of one crest is added to the positive amplitude of the other crest. The two waves combined will be stronger.