On Jan 26, 9:07*am, Cecil Moore wrote:
Keith Dysart wrote:
Computing Pf and Pr will yield 50 W forward and 50 W reflected.
And yet no current is flowing anywhere. The voltage on the line
is completely static.

Why would you compute Pf and Pr when no DC current is
flowing?

To facilitate learning about how the equations work and
what they may mean.

It is an invalid thing to do

Not at all. The equations don't just stop working at 0 frequency.

In their general form F(t), there is no hint at all that F can
not be a constant. Or, if you prefer, a square wave with a width
several times longer than the length of the line.

and unrelated to reality.

Anything unreal will also be unreal for the specific case of
sinusoids.

And yet some will claim that 50 W is flowing forward and 50 W
is flowing backwards.

I know of no one who will claim that for static DC.
There are obviously no photons being emitted and
therefore, no waves.

You really should try to stop thinking about photons
for just a short while. All the behaviours of a transmission
line can be understood and characterized without reference
to photons.

Analysis using classic circuit principles works quite fine
and has no difficulty at low frequencies.

Your example is unrelated to standing waves on an
RF transmission line where energy is in motion,
photons are continuously being emitted and absorbed,
and current and voltage loops are active.

There is no standing wave, but the example is quite
valid none-the-less. If you like, consider it as a
long pulse. And if you only want sinusoids, Fourier
will convert the pulse to sinusoids which you can,
using superposition, use to solve the problem.

The simplicity of the constant voltage makes it
easy to check your results.

One must realize the limitations of one's model.
The wave model obviously fails where there are no
waves.

Think of it as a long pulse. That should satisfy your
need to have 'waves'.

...Keith