Re: All that glisters is not gold

[William Beaty <billb@ESKIMO.COM>]

On Fri, 12 Feb 1999, Brian McInnes wrote:

> Paul, As I see it the problem with the plain old electric
> field is that, although it will explain the local
> acceleration of electrons along the wire, it doesn't really
> explain the transport of energy from the battery to the
> load.

Hi Brian!

As I understand it, the e-field doesn't REALLY explain the acceleration of
the electrons, since the KE of those electrons seems to appear from
nowhere. If we look at the field lines around an accelerating electron in
a field, we find changing e-field, which is the same as circular b-field,
which when crossed with the static e-field, gives an inward-directed
Poynting vector field.  The electron is "sucking energy" from the e-field
as it accelerates, and the e-field is slightly weaker after the electron
has passed.  The poynting-vector field seems to paint a clear picture of
how this energy is moving around.

When the electron is driven by the field, energy flows out of the e-field
and into the electron (the flow looks like it has a contracting torus
shape surrounding the electron, but perhaps it is actually spherical?)
When the electron drives against the field and deccelerates (such as after
a classical electron has bounced backwards from a lattice vibration or an
ion), then the electron is dumping energy into the field as it slows down.
(These backwards-moving electrons would charge up the entire circuit,
while the forwards-moving ones cause the whole circuit to discharge.)

>  That's why I like to invoke an electromagnetic field
> and the poynting vector (as apparently William Beatty does,
> judging by his contribution where he describes this model in
> excellent detail).

I didn't start it, I got it from a fairly old textbook which had a
treatment of the poynting-vector field surrounding a resistor.  The EM
energy in that situation contracts inwards around the resistor, like a
shrinking cylinder-shape. If the wires are like 1-ohm resistors
themselves, then we can draw a picture of the "lines" of energy flow.  If
we draw a schematic diagram, then we sketch in the e-field lines which
extend between different parts of the circuit, then it becomes trivia to
sketch in the "field lines" of the energy flow.  The poynting-vector
"lines" are simply the field that's perpendicular to the e-field in our
2-dimensional sketch.  Imagine a "charged" capacitor that's heating a
resistor.  The poynting-vector "stuff" comes flowing out of the dielectric
of the capacitor, pours along through the empty space that's surrounding
the pair of conductors, then dives into the resistor, entering its
surface perpendicularly from all directions.

I was forced to come up with this mental image because I wanted to answer
the question "what doees electricity look like?"  If "Electricity" equals
EM energy, then we can sketch a diagram of the flow of "Electricity" in
the space surrounding a DC circuit (and then quickly notice that this is
just like conventional RF twinlead waveguide stuff, but operating at DC!)

Weird delerious vision:  our entire civilization is run by radio waves.
Low frequency radio waves.  Guided by twinlead waveguides.  At 60Hz.  :)
(what would happen if an AC electric generator was connected to an
enormous dipole antenna, with 1/4 wavelength dimensions at 60Hz?  The
"electricity" energy-stuff would flow from the generator, run along the
connecting wires, then spew right out into space!)

Some of these issues are clearer if AC is involved: the electrons
generally sit in one place and wiggle, somewhat similar to air molecules
during a sound wave.  Do the electrons also move fast?  Yes, but then so
do the air molecules.  Judging from microscopic examination of air
molecules, we might predict that human being experience constant fierce
hurricain-like winds.  Instead we just experience air pressure and gas
diffusion phenomeona.  I like to imagine that electric circuitry is
similar:  the Drift Velocity is akin to wind or to water flow.  The actual
particle velocity is akin to the Brownian Motion movements of the fluid,
and is usually ignored when we work at a macroscopic scale.  High velocity
electrons do store "heat", and they might create electrical white-noise,
but at the same time they behave as if they are unmoving, just as a parcel
of air behaves as if it is unmoving when the wind does not blow.

((((((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))))
William J. Beaty                                  SCIENCE HOBBYIST website
billb@eskimo.com                                  http://www.amasci.com
EE/programmer/sci-exhibits          science projects, tesla, weird science
Seattle, WA   206-781-3320          freenrg-L taoshum-L vortex-L webhead-L