"Dave" wrote in news:ZPmWh.759$dM1.190@trndny07:


"Owen Duffy" wrote in message
...
Roy Lewallen wrote in
:

Correction:

Roy Lewallen wrote:

Superposition means the following: If f(x) is the result of
excitation x and f(y) is the result of excitation y, then the
result of excitation (x + y) is f(x + y). . .

That should read:

Superposition means the following: If f(x) is the result of
excitation x
and f(y) is the result of excitation y, then the result of
excitation
(x + y) is f(x) + f(y). . .
^^^^^^^^^^^
I apologize for the error. Thanks very much to David Ryeburn for
spotting it.


Fine Roy, the maths is easy, but you don't discuss the eligible
quantities.

As I learned the superposition theoram applying to circuit analysis,
it was voltages or currents that could be superposed.

Presumably, for EM fields in space, the electric field strength and
magnetic field strength from multiple source can be superposed to
obtain resultant fields, as well as voltages or currents in any
circuit elements excited by those waves.

For avoidance of doubt, power is not a quantity to be superposed,
though presumably if it can be deconstructed to voltage or current or
electric field strength or magnetic field strength (though that may
require additional information), then those components may be
superposed.

The resultant fields at a point though seem to not necessarily
contain sufficient information to infer the existence of a wave, just
one wave, or any specific number of waves, so the superposed
resultant at a single point is by itself of somewhat limited use.
This one way process where the resultant doesn't characterise the
sources other than at the point seems to support the existence of the
source waves independently of each other, and that there is no
merging of the waves.

Is anything above contentious or just plain wrong?

Owen

yes, superposition is meant to work directly on voltage, current,
electric fields, and magnetic fields. it can be extended by adding
appropriate extra phase terms to power or intensity as cecil prefers
to use.

you are at least partially correct. a measurement at a single point
at a single time can only give the sum of the fields at the instant of
measurement. make a series of measurements at a point over time and

Dave, I was continuing in the assumed context of coherent sources.

you can infer the existance of different frequency waves passing the
point, but not anything about their direction or possibly multiple
components. add measurements at enought other points and you can
resolve directional components, polarization, etc. assuming your
points are properly distributed... this means that a small probe
(like a scope probe) can only make a record of voltages/currents or
fields at a single point and can't tell anything about direction. add
a second probe and you could detect the direction of travel of waves
on a wire.

Yes, I understand.... Thanks.