Roy Lewallen wrote:
John Popelish wrote:

That's easy. RMS current is an AC measurement of current along the
conductor. Over any integer number of cycles, the total movement of
charge is zero. The current spends half the time going one way, and
half the time going the other way. This applies to both standing and
traveling wave induced currents. The only current that describes a
net movement of charge in a single direction is DC.


I see that Cecil is still having trouble with RMS, as well as with
current. Otherwise he couldn't have come up with the nonsense question

He seems to confuse energy in the wave traveling along a conductor
with the current it induces along that conductor, as it travels. I
have had a few such mental blocks and made a fool of myself a couple
times because I was sure I was right. But when the light finally came
on, lots of related things suddenly crystallized in my mind and I
jumped to a better understanding. One of my regrets is that I didn't
go back and apologize to my 7th grade science teacher for arguing with
him with so little tact, when I found out a year later that he had
been right and it was I who had been laboring under a misconception.
Same thing happened, on a different topic, in 8th grade science. So I
think I understand his attitude. I just hope that he sees that my
intentions are honorable, in this discussion. I am not attacking him,
but working for his understanding. I may be mistaken and end up
having another seventh grade moment here, but I'm not trying to
embarrass him.

In what direction is the RMS value of standing wave current flowing?

The RMS value of current doesn't flow. Charge flows, and current is the
rate at which it flows. RMS is one way of expressing the magnitude of a
time-varying current. In a steady state environment of pure sinusoidal
waveforms, any current can be expressed as Ipk * cos(wt + phi) where Ipk
is the peak value of the current, w (omega) is the rotational frequency,
and phi is the phase angle. This gives you precisely the value of
current at any instant in time, t. You can equally well express it as
Irms * cos(wt + phi) where Irms is the RMS value of the current. Nothing
is lost or gained by choosing one convention or the other, and using RMS
doesn't require abandoning the time varying or phase information. (In
EZNEC I chose to use RMS; NEC uses peak. They differ only by a constant
factor of the square root of 2. Both report phase angle along with
amplitude.) In either case, if you know or assume w, the current at any
instant is known if you know phi and either Ipk or Irms.

A point of clarification to John's posting:

When a standing wave exists on a transmission line, the phase of the
voltage or current is fixed (other than periodic phase reversals) with
position only if the end of the line is open or short circuited.
Otherwise, the phase of voltage and current will change with position.

Is that because the result is not a pure standing wave (superposition
of two equal and oppositely traveling waves), but a superposition of a
pair of traveling oppositely traveling waves of different amplitudes?