"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 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.