Phase Relationships: Interference Demo2 Interference   Interference is when a propagating wave encounters another object that may alter its path or change the amplitude in the medium. There are two types of interference: constructive and destructive. Two or more waves cross paths but do not interrupt the separate wave structure and as a result they either create a larger displacement or cancel each other; this is called the superposition of waves. In constructive interference, waves that cross paths while traveling in the same direction are considered to be in phase. This means the crests are in phase within the medium resulting in an amplitude equal to the sum of the separate amplitudes. If both amplitudes are equal, this doubles the resulting amplitude. Destructive interference is exactly opposite of constructive interference. Assuming that both waves have the same amplitude, when the crest and the trough line up, that is to say, when the two waves are out of phase, the result is an amplitude equal to zero. Demo1 Back to Phase Relationships To Top