Where Does the Power Go?
Jim Kelley wrote: As far as I know, there has never been any dispute
over which
direction the energy goes. The problem has always been with your
overly imaginative explanation for how it gets there.
I'm just quoting "Optics", by Hecht for how it gets there. Hecht's
irradiance equation tells the whole story. Total Irradiance = I1 + I2 +
2*SQRT(I1*I2)cos(A) where A is the angle between the I1 and I2 electric
fields. The last term is the interference term. If it is positive, the
interference is constructive. If it is negative, the interference is
destructive. If it is zero, the signals are orthogonal to each other
and no exchange of energy takes place. Please note that the dimensions
of Irradiance and the dimensions of average power flow vectors
(Poynting vectors) are the same. Hecht says that in the localized
absence of a source, any constructive interference must be equaled by
the same magnitude of destructive interference. The destructive
interference that eliminates reflections on the source side of the
thin-film coating on non-reflective glass is exactly offset by an equal
magnitude of constructive interference on the other side of that thin
film surface. It's all there in "Optics" by Hecht.
--
73, Cecil, w5dxp.com
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