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Re: Displacement Current Revisited

All,

        I haven't been following the displacement current thread really
well but
I think these may be the currents that my VI antenna picks up.  The antenna is
really two antennas.  One is sensitive to voltage or E fields and the other is
sensitive to current displacement.  This is demonstrated by the fact that the
wave forms are 90 out of phase from each other.

Just a thought,

        Terry



At 07:49 PM 3/12/99 +0000, you wrote:
>
>  To All -
>
>  Now that I have told the List that displacement currents don't exist I
>find after more research that these currents may exist in a different form
>compared to the regular currents we are accustomed to using when working
>with Tesla coils. If this is correct I owe apologies to the coilers who
>believed that displacement currents existed even though they were not clear
>in their understanding of these currents that are different.
>
>  Displacement currents around a Tesla coil may be real. However, coilers
>will probably never be able to measure them or use them in their
>calculations.  Currents are moving charges and there are moving charges
>surrounding all energized Tesla coils so coilers would be interested in
>knowing more about them.
>
>  Maxwell's equations are of a very general nature and can be used with
>several concepts of the electromagnetic field. One of these concepts appears
>to be in  the use of displacement currents. It is my understanding that
>certain equations derived from Maxwell's theories are based on moving charge
>DENSITIES. These densities are in the form of charges per unit volume.
>Displacement currents, therefore, would be current densities in a
>dielectric. In other words the moving charges around operating Tesla coils
>can be considered as displacement currents in the air (dielectric) around
>the coil.
>
>  The standard ammeter measures current intensities (quantities) not current
>densities (quantities per unit volume) so the displacement currents around
>Tesla coils cannot be be measured with the standard ammeter. This means that
>the equations using displacement currents could not be solved unless certain
>assumptions are made about the displacement currents.
>
>  Unlike currents in a conductor the density of displacement currents in a
>dielectric reduces as the distance increases. These currents (moving
>charges) must be measured by a different method. One method would be to
>place a special probe in the path of the moving currents which would induce
>an electrical effect in the probe to operate a meter, lamp, etc. The meter
>indication would reduce as the probe is moved away from the coil unlike the
>ammeter in a conductor circuit.
>
> The moving charges or displacement currents around the Tesla coil are
>called the electromagnetic field radiating from the Tesla coil. Note that
>the electromagnetic field is normally measured by radio engineers (or
>coilers) with a field strength meter measuring the "E" electric field not
>the current created by the "B" magnetic field!!?
>
>  The bottom line is that there appears to be a different type of current
>called displacement currents surrounding the Tesla coil. Coilers will not be
>able to measure these displacement currents with ammeters but they can
>possibly be measured with meters sensitive to other electrical effects.
>Coilers will also not be able to calculate these currents unless they are
>capable of solving the difficult theoretical equations.
>
> If we are to understand how a Tesla coil operates we wiil need to know more
>about the electromagnetic field surrounding the Tesla coil. I would be
>interested in hearing what other coilers think about the above. It should
>also be noted that more testing of these fields is required by the coilers
>with the coils and necessary measuring equipment.
>
>  There is much more to this story. Some of it came from "The Theory of the
>Electromagnetic Field" by David Cook and published by Prentice-Hall Inc. The
>rest is pure speculation by an electrical power engineer not a radio engineer.
>
>  John Couture
>
>--------------------------------------