Re: Displacement current
to: Richard WW, Scott, et al
A modern radio wave is certainly has displacement current elements. That is
one reason Maxwell's elegant equations predict the possibility of a radio
wave --- the idea of an electrical current flowing in a dielectric -- such
as a wave with both electric and magnetic components traveling thru the air.
The idea of a current flowing thru an insulator was unthinkable before
Maxwell demonstrated mathematically the concept of displacement current.
Extremely high vacuums are usually dielectrics, ie, non-conductive. A
modern x-ray tube for example has a very high vacuum otherwise it certainly
would not be able to hold off high potentials across its elements.
My comments regarding plasma tanks may has been misconstrued. I was
refering to a research plasma tank in which there is usually a high vacuum
with a plasma across a portion of the tank between electrodes or other
elements. A coaxial beam of microwave energy is usually employed to measure
currents in the plasma and plasma densities.
This is getting a bit off of TC construction, so thanks Terry for allowing
the discussion. This will close my posts on displacement currents.
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Saturday, March 06, 1999 6:24 PM
Subject: Re: Displacement current
>Original Poster: Scott Stephens <Scott2-at-mediaone-dot-net>
>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?
>>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
>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,
>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
>>and electric componets of a radio wave are regarded as displacement
>IIRC, displacement currents are an excuse to explain how waves can travel
>a vacuum, why it can support electric and magnetic fields. The model with
>its fictitous charge-carrying current is created to explain behavior
>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
>proof. Reactive currents must flow for this to occur, even if currents
>flowing through the 'ether' or transient polarizations of electron-positron
>>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
>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;
>where the field diverges at the plate fringes do the field lines not cancel
>I proposed taking a sheat of magnetic rubber, magnetized with the top of
>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
>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.