Re: Displacement Current Revisited

to: John, et al

To really understand displacement currents you have to go beyond classical
electrodynamics.  You need to study string theory.  The bad news is the math
is all 2nd order differentials and beyond the scope of many readers of this
list (certainly not all).  Trying to hash this out in classical
electrodynamics is really wasting your time.  Not trying to be negative here
at all --- just stating the facts as I know them to be.   When I was a
student I made the same mistake of trying to understand field theory with
classical electrodynamics and only later realized my folly.



-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Thursday, March 18, 1999 2:27 AM
Subject: Re: Displacement Current Revisited

>Original Poster: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net>
>  Greg, Terry, All -
>  Nothing apparently has happened to the notion that "displacement"
>are still considered to be caused by the changing E field. Cook gives the
>    Id = (eo)(dE/dt)
>  Id = Displacement current density
>  (eo)(dE/dt) = per Maxwell's equations
>  Cook also says that "Maxwell's equations are grounded in experiments".
>  He also writes "we must be cautious, for phenomena presently unknown
>well require modification of these equations in the future".
>  Does anyone know of new experiments that would have changed Maxwell's
>equations? How would this affect the electrical fields around Tesla coils?
>  This still leaves the question for coilers of how to measure the near and
>far electrical fields around a Tesla coil. Apparently this is also a
>question for radio engineers regarding radio transmitter antennas. The
>strength meters are not capable of measuring the near fields. Terman says
>the near fields do exist and are stronger than the E fields near an antenna
>(Tesla coil). Obviously radio engineers would be more interested in the far
>fields than the near fields.
>  Is it correct that Malcolm's LED's were energized by the far fields and
>Bart's lamps were energized by the near fields. How can you prove this?
>  To my knowledge the above issues have not already been hashed out.
>  Is the above too theoretical, not proper, or of little interest for this
>  John Couture
>At 09:02 PM 3/14/99 -0700, you wrote:
>>Original Poster: Greg Leyh <lod-at-pacbell-dot-net>
>>Original Poster: Terry Fritz <twf-at-verinet-dot-com>
>>>   I haven't been following the displacement current thread really well
>>>I think these may be the currents that my VI antenna picks up.  The
>>>really two antennas.  One is sensitive to voltage or E fields and the
>>>sensitive to current displacement.  This is demonstrated by the fact that
>>>wave forms are 90 out of phase from each other.
>>I haven't been following this either, but it seems that Maxwell's Eq's
>>are falling out of favor with some folks?  But they served us so well,
>>for so many years!
>>What happened to the notion that "displacement" currents are caused
>>simply by the changing E field, whether or not there are charged
>>particles present?  Many nifty antennas with low SWR's have been
>>designed and operated under this assumption, and they seem to launch
>>EM radiation quite well, even thru empty interstellar space.
>>Please ignore all this if the issue has already been hashed out.