When dealing with wave mechanics the principle of linear superposition specifies that when two or more waves interact they interfere with each other. This interference may be constructive or destructive interference. When wave crests match constructive interference takes place, when their form (phases) do not match destructive interference can occur. With identical waves (i.e., waves of the same wavelength and amplitude) emitted by the same source, the waves will undergo constructive interference if the distance traveled by one wave is equal to, or differs by an integral number of wavelengths from, the distance traveled by the second wave. Whenever path distances differ by exactly one-half a wavelength, the waves are completely out of phase and undergo complete destructive interference.

The general formulation of the superposition principle is that, when a number of influences act on a system, the total influence on that system is the...