# Re: Displacement current

```At 10:02 PM 3/3/99 -0700, you wrote:

Re: Displacement current

>Original Poster: rwall-at-ix-dot-netcom-dot-com
>
>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.

...

>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.

I think it is. Change the Eeff of space, or any other medium, and you change
its impedance, which is how much current will flow in it when an EMF or
voltage is applied. If space had 0 Eff, it would reflect all radiation, like
a perfect mirror.

>  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?

IIRC, displacement currents are an excuse to explain how waves can travel in
a vacuum, why it can support electric and magnetic fields. The model with
its fictitous charge-carrying current is created to explain behavior similar
to that of metalic conductors which were investigated & modeled first.
Consider that perspective, that the displacement current is an excuse,
invented as an explanation. Waves do travel through space. Your eyes are the
proof. Reactive currents must flow for this to occur, even if currents
flowing through the 'ether' or transient polarizations of electron-positron
pairs.

>Plasmas are not dielectrics either.

They can be. A strong magnetic field in a plasma will divert electrons &
protons from following a strait path through the plasma, so when high
frequency fields are present, the plasma appears capacitive. In combination
with the inductance of the path, you can set up resonances (ion & electron
cyclotron frequencies).

Similarly quartz crystals and other resonant devices can have extremely
large 'effective' inductances, even though their is no magnetic field.
Energy is oscillating in mechanical stress and momentum, rather than the
magnetic fields and current in this case.

>Also, do our TCs vibrate at microwave frequencies?

They vibrate at visible frequencies too, otherwise they would be invisible :-)
As the frequency goes into the X-ray region, electrons don't couple as well
anymore and the coil starts to turn invisible :-)

If magnetic fields can't be detected between the plates of a
plane-capacitor, maybe its because the B-field is circular and cancels; only
where the field diverges at the plate fringes do the field lines not cancel
each other.

I proposed taking a sheat of magnetic rubber, magnetized with the top of the
sheet one pole and the bottom of the sheet the other, and after cutting a
pattern into it, wrap it around a ping-pong or tennis ball.

Would you not have a magnetic monopole magnet? I think so. But I can't test
it because the rubber magnet sheet you buy is alternately polarized. I would
like to see a simulation (movie) of the field around a sheet as is is
deformed into a sphere. Then I might realy believe the field will disapear
when warped from a plane to a sphere.

```