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Displacement current
Dr Resonance wrote:
"It's not magic -- it's physics. A Tesla coil produces "displacement
currents" in air because the air represents a dielectric while the
terminal
represents a plate of a capacitor. The second plate is represented by
isotropic capacitance and plate to ground capacitance of nearby room
walls,
etc. A displacement current has unique and different properties than
normal
air to ground currents which produce the wandering spark phenomonea of
Tesla
oscillators.
You might read some early Maxwell for good descriptions of displacement
currents."
*********************************
All,
It is interesting to note that in Maxwell's day he invented the
displacement current on a whim as a logical and common sense item, even
though there is absolutely no conductive item in a capacitor's
dielectric to support the classic current seen in wires and metallic
conductors. It also made his equations a full featured set. This
current is found in all capacitor dielectrics, according to theory.
However, in a vacuum dielectric capacitor, it appears to generate no
magnetic field between the plates!!!!
This was most troubling to Maxwell and he wrote to several scientifc
friends that he hoped some proof of exisitance of the vacuum
displacement current's demanded magnetic field might be found in his
lifetime. It was not to be done however. As recently as 1994 Dr. D.F.
Bartlett of the Univ of Colorado made the attempt using an ultra
sensitive SQUID between two plates of a flat plate capacitor in vacuo.
.
He found 'zippo' mag field during charge or discharge. (this is a
though experiment as the wires to the cap and metallic plate elements
will create a field as we all know.) Being a lock step physicist he
struggled for an explanation in his paper. Ortherwise all sorts of
skeletons come out of the closet...(action at a distance, etc) He went
into an arcane mathematical diatribe using the now, for the most part,
disgarded Amperian current force laws to say that the circuit currents
in their flow and ebb create canceling mag fields via the plates. (most
folks cleave only unto the lorentz law which is in direct conflict with
ampere's old law.) The Lorentz laws somehow don't generate canceling
fields....Gee, sure wish they did.
Maxwell could see logical delema this in his own life time and was
adverse to using the Amperian current laws as they produce forces not in
line with his theory. It vexed him mightily and to his dying day he was
most concerned about the demanded, but seemingly missing magnetic field
in the interplate vacuum dielectric.
So by all means, read up on the displacement current. It is dished out
in huge helpings to all us engineers. Fortunately we don't need to fret
about mag fields inside our dielectrics so we never "auto-generate" the
question. Physicsists, however, are not so lucky.
While reading up on the THEORY it might be wise to heed the words of
Sir Frances Bacon from his essay on studies.................
."Read not to contradict or confute, nor to believe and take for
granted, nor to find talk and discourse, but to weigh and consider".
Richard Hull, TCBOR