Interference is the interaction of two or more waves. Waves move along their direction of propagation characterized by crests and troughs. Wherever two or more waves, either from one source by different paths or from different sources, reach the same point in space at the same time, interference occurs.

When the waves arrive in-phase (the crests arrive together), constructive interference occurs. The combined crest is an enhanced version of the one from the individual wave. When they arrive out-of-phase (the crest from one wave and a trough from another), destructive interference cancels the wave motion. The energy of the wave is not lost; it moves to areas of constructive interference.

Interference occurs in sound waves, light waves, shock waves, radio, and x rays. Waves display crests and troughs like the wiggles along the length of a vibrating jump rope. We see interference when ripples from one part of...