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Re: Capacitor charge, were is it?
Tesla List wrote:
<huge header snip>
> > All,
> > I brought up the point of the electrometer that Benjamin
> > Franklin used as a simple example of a device that contains no
> > dielectric. There are also simple instance were a charge can be
> > placed on normally nonconductive substances (i.e.: a rubber mat).
> > But this all roots itself back to a fundamental law of physics
> > we should all remember. Electron flow (i.e.: the bucket effect),
> > resides on the surface of an object. For example a wire containing
> > multple conductors will have less resistance than a solid conductor
> > will have. The reasons for this result are simple, more surface
> > area. This is also the same for capacitor construction. More surface
> > area to collect the charge and less distance between the plates
> > tends to increase the potential.
> >
> > In the reverse, more dielectric does not mean more charge
> > and more metal in the plates does not mean more charge. The key
> > here is surface effect.
> >
> > What does this mean? Well the charge is not in the dielectric! And
> > the charge is not in the plates either! Its on the surfaces of these
> > two different materials.
> >
> > Enough!
> > D. Gowin
>
> D.
>
> You have hit on what I have been saying all along about the dielectric/
> metal interface being the point of charge separation... IN A CAPACITOR
> AND A CAPACITOR ONLY! IF A CHARGED CAPACITOR IS DISMANTLED, THE CHARGE IS
> ONLY FOUND IN THE DIELECTRIC AND ZERO CHARGE IS RETAINED BY THE PLATES.
>
> Thus, you are right and wrong at the same time!
>
> Only a dielctric can store charge! In a capacitor the charge separation
> occurs at the metal/dielectric interfacial points. It is still held
> totally within the dielectric, however, until some closed metallic
> circuit conditon occurs and the energy enters the metal plates and goes
> off to do real work. The dielectric or space within the dielectric gives
> this charge up to a willing conductor in a closed circuit which can
> neutralize the charge held on the opposite side of the dielectric and not
> on the opposite plate of the capacitor. Sounds like semantics, but only
> one explaination works to explain experimental evidence.
>
> Richard Hull, TCBOR
Again, it's quite confusing to use the words 'energy' and 'charge'
interchangeably!! They really are very different things.
May I suggest that a section of above rebuttal should read:
_____________________________________________________________________________
"You have hit on what I have been saying all along about the dielectric/
metal interface being the point of charge separation... IN A CAPACITOR
AND A CAPACITOR ONLY! IF A CHARGED CAPACITOR IS DISMANTLED, THE _energy_ IS
ONLY FOUND IN THE DIELECTRIC AND ZERO _energy_ IS RETAINED BY THE PLATES.
Thus, you are right and wrong at the same time!
Only a dielctric can store (electrical)_ENERGY_! In a capacitor the..."
_____________________________________________________________________________
This makes a lot more sense to me, since _any_ isolated object with a
different number of positive and negative charges has a net charge,
regardless of its conductivity.
The electric field that emanates from any charged object contains a certain
amount of energy (not charge), depending the the dielectric constant of
the medium (1.00 for vacuum) and the total potential drop.
-GL