Re: Displacement Current Demonstration

On 13 Mar 2007 23:26:49 -0700, "Benj" <bjacoby@xxxxxxxxxxx> wrote:

Here's a simple question.

In Elecromagnetics there are lots of relatively simple experiments
that can demonstrate the various principles and fields.

But I've never seen one that can directly demonstrate a displacement
current. The usual argument seems to be that since the displacement
current hypothesis is necessary for Maxwell's equations to predict
electromagnetic radiation and since said radiation is known to exist,
therefore we doan need no steenkin' direct demonstration of a
displacement current.
Maxwell's equations apply best to the far field, where the fields have
no visible means of support. Yes, there we'd have to have displacement
current to complete the equations.
In the antenna ,currents flow to make the H field, so no displacement
current would be needed in the antenna. Near field is too complex to
try to discuss.

But, in a lumped constant device such as a capacitor, you can reason
out displacement current as being AC movement of displacement charge.
The problem becomes one of proving displacement charge.

This is easily done:
Since eps0 is regularly used to design capacitors as C = eps0 A/g
farads, then eps0 is real.
Connect a battery to a vacuum capacitor, and after a brief transient
inrush of current, the capacitor attains battery voltage V.
At this time we can say
E = V/g V/m and D = E*eps0 C/m^2 through the gap
Since there is no longer current, the wires can be disconnected. Now
we know the capacitor is still charged to V, and therefore there is
still a field E = V/g. But where do V and E come from?From the
displacement charges of the D field, where the D field has now become
a source instead of a sink::
E = D/eps0 V/m and V = E*g V
The charges in the gap are still trapped in their polarized positions
and as such are perfect standins for the field E and voltage V. The
field D does in fact produce E and V according to the equations above.

Now if you apply alternating voltage or current instead, the
displacement charge will oscillate in place in the gap and make
current density equal to
J = dD/dt C/m^2s & I = A*J coul/sec
The displacement charges lean right and left alternately to make the
displacment current.

But you may object, where do the charges come from? That's the
question I asked myself, that caused me to do the analysis in my
permittivity paper. And that's how I was led to conclude there was
another space, a dual to our universe.

Does anybody here know of any direct experimental demonstration be it
simple or complex of the existence of a true displacement current.
Even a reference to a paper where someone has done it?
I know a simple experiment but I think I'll wait a bit.
Benj
John Polasek
.

Relevant Pages

  • Re: Displacement Current Demonstration
    ... If Displacement Current is not the *cause* of a magnetic field, ... It appears that it comes from the motion of charges as they are drawn toward ... together a fairly short description of what happens in a capacitor and it is ... The displacement current is supposed to make the whole thing work. ...
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  • Displacement current in MOSFET
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    (sci.electronics.basics)