This applet models the constructive and destructive interference of two waves with the same wavelength. Click on the "phase+" to increase the phase difference, and click on "phase-" to decrease the phase difference.
The top wave (in red) does not change. The second wave (in blue) shifts it phase relative to the top wave by an amount selected by the user (in degrees). The bottom wave (in purple) is the algebraic sum of the two upper waves.
As the phase is shifted, the wavelength of the bottom wave is unchanged, but the amplitude either increases (for constructive interference) or decreases (for destructive interference). This effect of the phase difference on the amplitude of the sum of two waves is a peculiarity of wave behavior, and it was this phenomenon which led Thomas Young in 1800 to conclude that light was a wave, and not a particle (as had been previously suggested by Benjamin Franklin).
© 2003-2011 by Lawrence T. Sein. All rights reserved.
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