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 The Physics of Light

# Interference

Interference is the interaction between waves traveling in the same medium. When two waves come into contact, depending on the phase differences along the waves, constructive and destructive interferences will occur.

In constructive interference, the amplitude of the wave is amplified. This happens when the two waves are in phase -- if the crests and troughs of the waves coincide with each other. Consider two waves, one with a crest of +1 units and coinciding with a wave of +2 units in amplitude at that point, traveling in opposite directions on the same medium. When these troughs come into contact, the resulting amplitude will be the sum of the two waves, which is +3 in this case. Once the waves pass each other, however, they will resume their original course with their original amplitude -- as if they have not been disturbed at all.

Destructive interference is very much like constructive interference except that the two waves cancels out each other. This happens when the waves are out of phase -- when the crests of one wave coincide with the troughs of the other. Consider two waves, one with a crest of +1 coinciding with a wave of -2 units in amplitude at that point, traveling in opposite directions on the same medium. At the point of contact, the resulting amplitude will be the difference of the two waves, which is -1 in this case. Just like constructive interference, once the waves pass each other, they will resume their original course with their original amplitude -- as if they have not been disturbed at all.

Next article: Diffraction? Yes, it also bends around.

 Interference Quantum Mechanics

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