Since sinusoidal waves are cyclical, a particular phase difference between two waves is identical to that phase difference plus a cycle. For example, if two waves have a phase difference of π4, the interference effects would be the same as if the two waves had a phase difference of π4+2π. The complete criterion for constructive interference between two waves is therefore written as follows: phase difference=0+2πnfor any integer n Write the full criterion for destructive interference between two waves