Re: Phase cancellation --where does the energy go?

DTebar@xxxxxxxxx wrote:
Hi,

If the amplitude of two waves are cancelled by adding them 'out-of-
phase'. What happens to the energy?

--Daniel Tebar


Basically, you cannot get canceling interference without having amplifying interference somewhere else. Somewhat simplistically, the cancellation somewhere gives zero amplitude hence zero energy, but the amplifying interference elsewhere gives twice the amplitude thus four times the energy: the average energy density is twice that of either wave, just as it's supposed to be.

Actually, I'm cheating a little: you'd normally prove energy conservation from fundamental laws, and then use this to prove my explanation (that you can't get cancellation only) rather than the other way around. Kind of demonstrates the power of conservation laws, doesn't it? :-)

Einar

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