Cecil Moore wrote:
John Popelish wrote:

When you talk about current flowing, you seem to be thinking of
current waves traveling along a conductor. Others seem to be saying
"current" and thinking of charge movement. I think that only the
second is technically correct ...


John, many thanks for some rationality from a cool head.

Conventions aside, that sounds about right. So would you agree
that if there's a forward current of one amp

By this I assume you mean a traveling current wave with an RMS value
of 1 amp.

and a reflected current of one amp,

Meaning a returning current wave with an RMS current of 1 amp.

the net charge movement is zero and therefore
the standing wave current is not "going" anywhere?

Sorry, no. There is no net (average over one cycle) current, whether
the wave is traveling or standing. In both cases the instantaneous
current changes direction every half cycle at any given point. If
there is a standing wave made of a 1 ampere RMS current wave and a 1
ampere RMS returning wave, then the standing wave current will vary
from zero amperes RMS at current nodes to 2 amperes RMS at current
peaks. Looking just at just current, and at only a single point, a
traveling current wave and a standing current wave are
indistinguishable. You cannot tell if the measured RMS current is
made up of a wave traveling in one direction, or the sum of two waves
traveling in opposite directions.

How can something with a constant fixed phase angle of zero degrees "go" anywhere?

The only way to understand a standing wave having a phase of zero
degrees, that makes sense to me, is that it applies to all points
between one current node and the next. The points between the next
two nodes have a phase of 180 degrees (charge is moving in the
opposite direction at all times) with respect to the points between
the first two nodes. So, if you pick some point between a pair of
current nodes, all other points along the standing wave must be either
be in phase with the current at that point, or 180 degrees out of
phase with it. In a standing wave, charge sloshes back and forth in
opposite directions between alternate pairs of current nodes.
Likewise, where the charge piles up and sinks (at the current nodes),
voltage peaks occur because of the charge accumulation or shortage.

Standing waves involve no net wave travel in either direction, though
anywhere except at the current nodes, charge is certainly moving back
and forth along the conductor, during a cycle.


That's unclear to me. Why can't the E-field and H-field simply be
exchanging energy at a point rather than any net charge moving
laterally?

In an isolated EM plane wave, I think this is the case, and
displacement charge in space takes the place of conductor current.
But when a wave is guided by a conductor, we can measure the charge
sloshing back and forth in the conductor in response to those fields.

Take a look at:
http://galileo.phys.virginia.edu/cla...axwell_Eq.html
about half way down.

Here is an excerpt:

(begin excerpt)

"Displacement Current"

Maxwell referred to the second term on the right hand side, the
changing electric field term, as the "displacement current". This was
an analogy with a dielectric material. If a dielectric material is
placed in an electric field, the molecules are distorted, their
positive charges moving slightly to the right, say, the negative
charges slightly to the left. Now consider what happens to a
dielectric in an increasing electric field. The positive charges will
be displaced to the right by a continuously increasing distance, so,
as long as the electric field is increasing in strength, these charges
are moving: there is actually a displacement current. (Meanwhile, the
negative charges are moving the other way, but that is a current in
the same direction, so adds to the effect of the positive charges’
motion.) Maxwell’s picture of the vacuum, the aether, was that it too
had dielectric properties somehow, so he pictured a similar motion of
charge in the vacuum to that we have just described in the dielectric.
This is why the changing electric field term is often called the
"displacement current", and in Ampere’s law (generalized) is just
added to the real current, to give Maxwell’s fourth -- and final --
equation.

(end excerpt)