Re: Displacement Current Demonstration

Hello Benj...

You don'yt have to decode the .gif files. I did a re-posting of the
derivation. I apologize for the inconvenience, but I did not know how to
imbed equations in a posting. Now I do!

Part of the problem with Displacement Current is that the magnetic field
supposedly associated with it is *very* weak. All the "derivations" that I
have seen set out to "prove" that the magnetic field inside the gap between
two capacitor plates is the same asit if the gap had been filled with a
conductor.

But in a real capacitor, the gap is extremely small. So the task is to
measure the (supposed) magnetic field inside the gap (a mm or so in width)
in an environment containing meters of wires containing magnetic fields
caused by the exact same current's frequency and phase. This task makes
finding a needle in a haystack seem trivially simple by comparison.

Enclosing the capacitor in a black box and attempting to measure what is
inside seems doomed to failure. Magnetic fields from the capacitor would
meld together with fields from the connections such that it would make the
task of measuring H inside a capacitor look simple!

And yes, I am convinced that the shape of the capacitor will control the
shape of the fields. That's what my post labeled "Field Finder Software" is
all about. So far, I have received no replies. #SIGH#

Bill
"Benj" <bjacoby@xxxxxxxxxxx> wrote in message
news:1174429514.720323.176860@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Bill Miller wrote:
Hello Benj...

If Displacement Current is not the *cause* of a magnetic field, thus
satisfying the well known Dell cross H = J + dD/dt, then where the *H*
does
the H come from?

It appears that it comes from the motion of charges as they are drawn
toward
the surface/"pushed" away from the surface by the E field. I have put
together a fairly short description of what happens in a capacitor and it
is
shown below: (I think... I've not tried to append rich text before.)

Forgive me that I haven't yet decoded your .gifs and followed your
arguments, but I still want to comment before I do that.

Yes, the question where indeed does the H come from. And it's worse
than that. If you look for example in a textbook like Plonsey and
Colin you'll find the usual statements that that if you have a "black
box" with a capacitor in it and you measure the magnetic field about
it, you can't tell what kind of capacitor is in there even though
Ampere's law fails if you compute it through the gap of the capacitor.
The displacement current is supposed to make the whole thing work.

So the question in my mind is indeed where does the H come from and
furthermore, if it comes from charge motion on the capacitor plates,
shouldn't it then create a magnetic field outside the "black box"
which is dependent upon the GEOMETRY of the given capacitor rather
that the implied "can't tell what's in the box" scenario?

These were the musing that got me wondering if indeed anyone had
actually tried any of these displacement current "black box"
experiments and tried to see if a field was indeed generated
independent of the capacitor geometry? And especially if an H field
can be generated in free empty space from a changing E field which is
the theory behind electromagnetic radiation. What kind of mechanism
can we imagine that would do that?

Benj



.

Relevant Pages

  • Re: Displacement Current Demonstration
    ... Bill Miller wrote: ... the gap is extremely small. ... measure the magnetic field inside the gap ... displacement current directly, so to speak. ...
    (sci.physics.electromag)
  • Re: Displacement Current Demonstration
    ... Part of the problem with Displacement Current is that the magnetic field ... have seen set out to "prove" that the magnetic field inside the gap between ... But in a real capacitor, ... a vacuum if it carries electron pairs constrained to ...
    (sci.physics.electromag)
  • Re: Displacement Current Demonstration
    ... But in a real capacitor, the gap is extremely small. ... measure the magnetic field inside the gap ... displacement current directly, so to speak. ...
    (sci.physics.electromag)
  • Re: Cancel displacement current?
    ... Robert kenworth wrote: ... magnetic field in opposition to the intenal B field of the capacitor? ... across the capacitor's plates. ...
    (sci.electronics.design)
  • 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. ...
    (sci.physics.electromag)
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