On Jun 1, 5:44*pm, K1TTT wrote:
no, it is not obvious. *where do you draw the line... 1 degree, .1
degree, .001 degree? *at what point is the angle small enough to say
that they have 'interacted' and the energy is redistributed?

I don't know the answer but zero degrees (perfect collimation) will
result in interaction.

i propose that 'cancellation' is just a special case of interference
where the waves are 'close enough' to collinear that you never see the
interference pattern.

When b1 = s11*a1 + s12*a2 = 0 at an impedance discontinuity, wave
cancellation has taken place. s11*a1 and s12*a2 are coherent sine
waves, equal in magnitude, and 180 degrees out of phase. Have you read
the FSU web page where they describe wave cancellation? All these
concepts are old hat to optical physicists.

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/
waveinteractions/index.html

"... when two waves of equal amplitude and wavelength that are 180-
degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction
of light."
--
73, Cecil, w5dxp.com