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July 29th 05, 09:41 PM

On Fri, 29 Jul 2005 13:42:49 -0500, (Richard
Harrison) wrote:

Tor, N4OGW wrote:
"You CANNOT superimpose POWERS, or even talk about the "power" of
various reflections in the same media."

Hi Richard,

Given the original subject line has been munged up, it is difficult to
know if you were responding to Tor directly, or through another
posting. Either way, it would be instructive to complete his quote,
as follows:

However, your understanding of superposition is wrong. You
CANNOT superimpose POWERS, or even talk about the "power" of various
reflections in the same media. You can only add the wave amplitudes
(electric fields). THEN you take the total amplitude and square that
to get the power.

which seems to "square" with where you take this:

It is done all the time. P=Esquared / R = Isquared x R.

Of course the topic has drifted into this problem of superposition
which has been approached before along similar lines. The truth of
the matter in the thin film discussion is that it doesn't require a
complete solution of either electric fields or power to realize that
"total cancellation" of the waves described in the example is
impossible.

It is quite evident that through the actions of the first interface,
that there is less energy incident upon the second interface.
Further, given that both interfaces operate with identical reflective
and transmissive properties, it follows the second interface could not
reflect enough to totally negate the reflections of the first.

Torr had a question in this regard, but as he is a casual
correspondent we have not seen any further comment from him - nor
would I expect him to have amplified on your observation above.

73's
Richard Clark, KB7QHC

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