Definitions
Constructive Interference: The enhancing interference that occurs when two waves occupy the same space at the same time and both disturb the medium in the same way so that the disturbance is larger than the disturbance of either wave separately.

Destructive Interference: The canceling interference that occurs when two waves occupy the same space at the same time and both disturb the medium in opposite ways so that the disturbance is smaller than the disturbance of either wave separately.



In the animation we show two waves moving through the same medium. The first wave, shown in red, is moving from left to right; the second, shown in green, is moving from right to left. In this case they both have the same wavelength and amplitude. But when they meet, they interfere to produce the wave shown in black. Observe the place where there is "constructive interference." The resulting black wave has twice the amplitude of either the green or red waves. However, where there is "destructive interference," the red and green waves neatly cancel each other out. As time goes on, these positions of constructive and destructive interference remain in the same place. The position of destructive interference is sometimes called a "node." The position of constructive interference is called an "antinode."

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