Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:

Who said powers can never be added?


Must have been someone who was unfamiliar with the expression 'figures
can lie and liars can figure'. :-)


You reckon Eugene Hecht was lying when he shows us how to
add two irradiances to obtain the total irradiance (power
per unit-area) in _Optics_?

Eugene Hecht doesn't have a dog in this fight, Cecil. But the quote is
a truism that applies in any case. Wrong numbers added correctly
produce a wrong number; correct numbers added incorrectly produce an
incorrect number; and in the special case, certain wrong numbers added
in a particular incorrect way can produce a desired result.

You take too great a liberty with the name Eugene Hecht. Among the
things which won't be found in any of Dr. Hecht's texts is a minus sign
in front of number expressing an irradiance. Nor will we find a
negative scalar quantity accompanied by the claim that the negative sign
indicates a change in direction, as you have done. Eugene Hecht also
did not claim that interference could be a cause for energy to reflect
or otherwise change direction, as you have done. Such claims are
blatently false.

Power and irradiance are derived and dependent quantities, not
fundamental independent quantities in nature. And although an
automobile moves at some speed, the scaler quantity itself is not
something which moves. Similarly, power and irradiance do not
physically propagate and they do not physically interact. 'They' do not
reflect, refract, diffract, disperse, interfere, or act upon other
'powers' or 'irradiances'. JC Maxwell and others observed that it is
electric and magnetic fields which propagate, interact with matter, and
add algebraically and vectorially. When fields physically interact with
matter, we can measure their effect and can quantify such things as
voltage, current, and heat, and hence calculate such things as power or
irradiance. But it is actually the fields themselves which
algebraically sum. Of course the interference equation accurately
expresses power and irradiance. The fact that power and irradiance
generally go as the square of the fields allows us to correctly make
certain additional mathematical assumptions. One must still be careful
not to mistake an effect for a cause. But it is the 2nd Amendment, the
internet, and the absence of peer review which afford men the freedom
and means to work equations and describe physical phenomena in any way
they like.

73, ac6xg