Diffraction

The top two waves are summed to give the third wave. When the top two waves are out of phase, destructive intereference occurs, decreasing the amplitude of the third wave.
Constructive interference occurs when waves are in phase; destructive interference occurs when the waves are out of phase with each other.

A laser beam passing through a decreasing slit formed by two razor blades.
Destructive interference occurs in a CD when land changes to a one-quarter wavelength deep pit..

Diffraction | Build a Better CD Player | ChemConnections

The top two waves are summed to give the third wave. When the top two waves are out of phase, destructive intereference occurs, decreasing the amplitude of the third wave.	Constructive interference occurs when waves are in phase; destructive interference occurs when the waves are out of phase with each other.
A laser beam passing through a decreasing slit formed by two razor blades.	Destructive interference occurs in a CD when land changes to a one-quarter wavelength deep pit..