Re: Displacement Current Referances

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Antonio,

At 11:15 AM 3/9/2002 -0300, you wrote:
>Tesla list wrote:
>> 
>> Original poster: "SF by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><sfusare-at-adelphia-dot-net>
>> 
>>     Here are a few referances that some may find interesting per the
>> debate on the displacement current
>> and the presence or absence of an associated B field:
>> 
>> D. F. Bartlett (Professor - University of Colorado Boulder), "Conduction
>> current and the magnetic field in a circular capacitor"
>> American Journal of Physics #58 (12), p 1168 - 1172 (1990) (Squid
>> detects no B field to accompany displacement current
>> in a slowly discharging capacitor. B field that is detected is fast case
>> can also be described using the conduction current flowing
>> in the plates)
>
>I looked at this paper today, and also at some of its references.
>They appear to be correct (and AJP is a serious peer-reviewed journal). 
>In the described cases, all the magnetic field can be explained by 
>currents in the wires and capacitor plates.
>(As I was already suspecting...).
> 
>> Granted that an academic title does not automatically confer competence.
>> Also granted that both Dr. Jefimenko
>> and Dr. Bohren completely avoid mention of the unpleasant side effects
>> of the theory they posit (so how does
>> a TEM wave propagate?). But the works (Jefimenko's in particular) are
>> very well done and bear reading by
>> those on both sides of this debate.
>
>I think that the trick is that these analyses assume "quasi-static"
>conditions, where there is no irradiation, the potentials at all
>conductors are uniform, and everything happens instantaneously.
>When these conditions are not met, the "displacement current" 
>appears, with its associated magnetic field. The conditions that 
>make this happen are quite difficult to reproduce experimentally
>in a way that allows easy measurements, and also difficult to analyze 
>precisely. 
>I am thinking about an experiment to show what really happens.
>
>Look here (and look at the comment at the end):
>http://www.physics.umd.edu/deptinfo/facilities/lecdem/k2-63.htm
>
>Antonio Carlos M. de Queiroz
>
>

The lab demonstration appears to have been set up and was working great!...
 Until someone said that you couldn't measure the magnetic fields of
displacement currents :o)))  Then "some discussion" occurred that "some
sort" of "general electromagnetic pickup" was going on...  Thus, it is now
a lab demonstration to "perhaps demonstrate something" :-))  "almost" as
bad as the plant experiment ;-D

Apparently they could not resolve the issue either...

This is much like the experiment we were thinking about where we would use
the Pearson current monitor to "look" for the magnetic field.
Unfortunately, the metallic coil we place between the plates is going to
bend and twist the electrostatic E fields terribly and generally mess
things up.

We either need a small ground potential (hooked to scope) sensor directly
in the center of the plates (where a ground potential has minimal effect
within a balanced AC* field) or an electrically isolated magnetic sensor.
But first we must determine the magnitude of the fields we are looking for
to be sure they are within the ability to measure and do a few other sanity
checks just so we know the nature of the beast we are searching for.  I
don't worry too much about conduction currents since I can control their
direction and maybe cancel them out at least in the mid plane of the capacitor.

In general, this setup up is nice, simple, and, reproducible.  We should be
able to "fix" it to eliminate the "some sort of general electromagnetic
pickup" problem and clearly show the displacement current magnetic field.
Unless, of course, it is not there.  In that, case we will see nothing.  If
such an experiment can be formulated, the results should be definitive.
However, as Scott's references point out, some pretty high powered folks do
not seem to have done this seemingly simple thing...  I guess we should be
very afraid ;-))

*maybe that should be ApC field.  "Alternating perhaps Current" field :O))

Cheers,

	Terry