Keith Dysart wrote:

On Jan 3, 12:55pm, Mike Monett wrote:

[...]

Your explanation is easily proven false. Let's suppose it was
true.

Suppose it was possible to introduce a pulse of charge onto a
conductor.

Since like charges repel each other, what keeps the pulse
together? In other words, what prevents it from destroying
itself?

Then, when the first pulse meets the second, what mechanism
allows them to bounce off each other?

Then, after they have bounced off each other, what mechanism
keeps them together?

All good questions.

For which you have no answers.

But there's more bad news. Here's your original post of Dec 29:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
Subject: Standing-Wave Current vs Traveling-Wave Current
Date: Sat, 29 Dec 2007 14:33:46 -0800 (PST)
From: Keith Dysart
Newsgroups: rec.radio.amateur.antenna

Keith Dysart wrote:

[...]

Consider a 50 ohm transmission line that is 4 seconds long with a
pulse generator at one end and a 50 ohm resistor at the other.

The pulse generator generates a single 1 second pulse of 50 volts
into the line. Before and after the pulse its output voltage is 0.

While generating the pulse, 1 amp (1 coulomb/s) is being put into
the line, so the generator is providing 50 watts to the line.

After one second the pulse is completely in the line.

The pulse is one second long, contains 1 coulomb of charge and 50
joules of energy. It is 50 volts with 1 amp: 50 watts.

Let's examine the midpoint (2 second) on the line.

At two seconds the leading edge of the pulse arrives at the
midpoint. The voltage rises to 50 volts and the current becomes 1
amp. One second later, the voltage drops back to 0, as does the
current. The charge and the energy have completely passed the
midpoint.

When the pulse reaches the end of the line, 50 joules are
dissipated in the terminating resistor.

Notice a key point about this description. It is completely in
terms of charge. There is not a single mention of EM waves,
travelling or otherwise.

Now we expand the experiment by placing a pulse generator at each
end of the line and triggering them to each generate a 50V one
second pulse at the same time. So after one second a pulse has
completely entered each end of the line and these pulse are racing
towards each other at the speed of light (in the line). In another
second these pulses will collide at the middle of the line.

What will happen? Recall one of the basics about charge: like
charge repel. So it is no surprise that these two pulses of charge
bounce off each and head back from where they came. At the center
of the line, for one second the voltage is 100 V (50 V from each
pulse), while the current is always zero. No charge crossed the
mid-point. No energy crossed the mid-point (how could it if the
current is always zero (i.e. no charge moves) at the mid-point.

[...]

So do the travelling waves "reflect" off each other? Save the term
"reflect" for those cases where there is an impedance
discontinuity and use "bounce" for those cases where no energy is
crossing a point and even Cecil may be happy. But bounce it does.

Keith

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
In order for the pulses to bounce off each other, your theory
requires that electrons move at nearly the speed of light.

Unfortunately, they do not. The classical formula for the drift
velocity of electrons in a conductor is:

v = I / (n * a * q)

where

v is the drift velocity of the electrons

I is the current in Amperes

n is the number of electrons per cubic metre, copper = 8.5e28 / m^3

A is the cross sectional area of the wire

Q is the charge of an electron, 1.6e-19C

References:

http://amasci.com/miscon/speed.html

http://physicsplus.blogspot.com/2007...electrons.html

http://resources.schoolscience.co.uk...elech2pg3.html

http://hyperphysics.phy-astr.gsu.edu...ic/ohmmic.html

Using the 1 Amp from your post, if the center conductor has an area
of 0.5 mm^2 (0.5e-6 m^2), the drift velocity is:

v = 1 / (8.5e28 * 0.5e-6 * 1.6e-19)

= 0.0001470 meters per second

So in one second, the electrons move 0.147 mm.

If the propagation constant of your line is 66%, the signal will
propagate at:

Vel = 3e8 * 0.66
= ~200e6 meters/sec

If the pulses meet in the center of the line, that point is about
400 million meters away from the electrons that originally carried
your pulse of charge.

This raises many questions. How can the pulses bounce off each other
if the electrons that carried the charge are 400 million meters
away? Obviously, they can't.

There's more bad news. If two collections of 1 Coulomb each were
concentrated one meter apart, the force between them could be
calculated from Coulomb's Law. In this example, the force is 1.01
million tons:

http://hyperphysics.phy-astr.gsu.edu...ic/elefor.html

This means the pulses could not even come close enough to bounce off
each other. This would certainly wreck any timing analysis you try
to do on the signals.

So your theory fails simple logic tests, it requires invalid
electron velocities, and it fails Coulomb's law.

It is clear the pulses cannot bounce off each other, as you claim
above when you state "But bounce it does."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
But it appears that your underlying suggestion is that charge and
charge flow in the distributed capacitance and inductance can not
be used to analyze transmission lines.

That is not what you proposed. Your post states:

Notice a key point about this description. It is completely in
terms of charge. There is not a single mention of EM waves,
travelling or otherwise.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
And yet I commonly see discussion of current in transmission
lines. Current is charge flow per unit time. Is this all invalid?

Must we abondon measurements of current? Voltage? These are all
based on the assumption of charge being a useful concept.

You are just trying to fog the issue. You cannot use charge by
itself as you claim above.

Keith

Regards,

Mike Monett