Folks this is thread has devolved into one of the various mythologies of
mis-used language: Let us remember that "fields" don't really exist; they
are inventions -- mathematical constructs if you will -- which are supposed
to make our calculations easier. Like many such constructs in other
places, it is OK to use anthropological language but only as long as one
realizes what it rally happening.
|... 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.
Well maybe yes, but remember that to calculate what happens to the
electron, one considers _only_ a "field" due to all _other_ sources -- It
makes no sense to talk about an electron which is moving in a field due to
it's own charge.
|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.
I have no idea what "sucking energy" might mean. The _only_ way for an
electron to gain energy is for something to do work on the electron.
Energy is not just floating about to be "sucked".
|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?)
It makes no sense to me to say that "energy flows out of the E-field.
Perhaps others can explain this to me and use terms that make sense.
Certainly there is no "energy" _in_ the field to flow anywhere.
|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.)
"Dumping energy" -- one could say "doing work", but one would have to say
how that work is done.
|> 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
We all should have learned by now that "old textbooks" are full of
mythology and mythological language and hand waving. Sometimes this hand
waving solves engineering problems -- often it does not.
Etc, etc, etc etc.
|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