Interference
When two waves of the same frequency and moving in the same direction meet, the resulting wave is the additive combination of the two waves. In the special case where two waves have the same electric field amplitude (wave height) and are in phase, the resulting amplitude is twice the original amplitude of each wave and the resulting frequency is the same as the original frequency of each wave. This characteristic is called constructive interference. In the special case where two waves have the same electric field amplitude and are 180° out of phase, the two waves cancel each other out. This characteristic is called destructive interference.