Re: Displacement current

On 03/01/99 19:11:44 you wrote:
>Original Poster: "Dr. Resonance" <Dr.Resonance-at-next-wave-dot-net> 
>to: Rich Hull
>Displacement currents do exist and they do have a magnetic field.  A common
>example of displacement current is a EM wave, ie, radio.  It has both a
>magnetic and electric component.  At UW (Wis) and Sandia they measure
>displacement currents and magnetic fields in plasmas almost on a daily

The question before us is that of displacement current in a dielectric.  
Would you explain displacement current in an EM *wave*, ie, radio?  Certainly 
a radio wave traveling in free space is not in a dielectric.  There is some 
confusion as to magnetic and electric componets of a radio wave being 
identified as a displacement current.  Would you please explain why magnetic 
and electric componets of a radio wave are regarded as displacement currents?

Plasmas are not dielectrics either.  They are highly conductive and certainly 
EM currents are readily conducted by them.  No need for displacement currents 
to explain anything here.  I'm sure magnetic fields are present in plasmas and
are detected routinely detected by the above institutions.  But, once the 
plasma conducts it's just plain EM.  Same as a TC plasma discharges caused by 
electrostatic potentials.  RWW

>A SQUID is not the proper type of probe for this type of experiment.  The
>problem is that the magnetic field is very small even though the current is
>very high --- the current is spread out through the entire plate area and
>usually only amounts to 1/2 to 1 ampere per cm squared even in caps firing
>thousands of amperes in discharge mode.  The current density is very small
>and the SQUID would be a very poor choice as a measuring instrument for this
>magnetic field.  In this experiment you described the SQUID would only
>measure 1/2% (or less) of the total magnetic field in the area and may not
>produce any results at all --- as you described.

I disagree.  Squids are sensitive in the extreme.  Detecting even even 1/2%
of the magnetic field in an area is not at all challenging for a squid.  They 
are the most sensitive magnetic field detectors known to man.  RWW

>The second problem is a vacuum has a very low dielectric constant.  To
>properly conduct this type of experiment a very high dielectric constant
>material such as barium titanate would be used and microwaves would also be
>employed.  It can and is daily measured in a vacuum but with microwaves not
>low frequency waves --- the magnetic field value is so low at low
>frequencies it is nearly impossible to measure -- at least extremely

Aren't displacement currents by definition of equal magnitude to the currents 
they are supposed to displace?  Why would they be so small and difficult to 
detect?  At any frequency?  If Maxwell is right, they should be detected at
frequency and very easily.  Things really get strange when you excite matter 
with very high frequencies such as microwaves.  There are mutiple resonances 
on a molecular, atomic and nuclear levels.  I'm sure everyone has heard of
magnetic resonate phenomena.  Same goes for vacuums.  It is impossible to
a very good, let alone absolute, vacuum here on earth.  I'm sure manmade 
"vacuums" contain enough gas molecules to resonate when stimulate by a strong 
electromagnetic field such as a microwave.

Also, do our TCs vibrate at microwave frequencies?  Wouldn't the energy
in nongrounded sparks, which you claim is from displacement currents, far
any possible displacement current produced in a low dielectric air at the
low frequencies of our TCs?  RWW

>Maxwell's frequencies were relatively low even after Hertz proved their
>existence.  Only during the "big bomb" research during WWII did accurate
>methods of measuring displacement currents develop using magnetrons and
>better dielectrics.
>This data from my old group at UW-Wisconsin.
>Also, if you happen to have the reference on Dr. Bartlett's work one of them
>would like to look it up for reference.  Please advise.

Please provide the references and data you cited from your old group at UW 
and Sandia confirming the existence of displacement currents in dielectrics
discribed by Maxwell.  I'm sure Richard Hull will do the same.

Richard Wall