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From harmonic addition theorem,  any superposition of harmonic waves
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(1) |
is itself a harmonic wave
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(2) |
where
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(3) |
and
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(4) |
If the waves are coherent so that they all have the same amplitude and phase, then
 for all i and
j, so
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(5) |
and (3) becomes
Assume that all waves are incident with the same amplitude. For a sufficiently large number of randomly oriented phases
 ,
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(7) |
and (3) becomes
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(8) |
© 1996-2007 Eric W. Weisstein
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