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Re: Capacitor charge, were is it?

Tesla List wrote:
> 
> > Subject: Re: Capacitor charge, were is it?
> 
> >From gowin-at-epic-1.nwscc.sea06.navy.milMon Oct 28 21:42:42 1996
> Date: Mon, 28 Oct 1996 09:52:27 -0500
> From: Dan Gowin <gowin-at-epic-1.nwscc.sea06.navy.mil>
> To: tesla-at-pupman-dot-com
> Subject: Re: Capacitor charge, were is it?
> 
> Tesla List wrote:
> >
> > >From ed-at-alumni.caltech.eduSat Oct 26 23:37:23 1996
> > Date: Sat, 26 Oct 1996 10:04:22 -0700 (PDT)
> > From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Capacitor charge, were is it?
> >
> > "There is a classic problem in which two identical capacitors are connected
> > with a switch. Before the switch is thrown one capacitor has a certain
> > voltage, the other none. If we give numbers, let's say C=1uF and V=1000V on
> > the first capacitor. The energy is (cv^2)/2 = 0.5 joules. Now after the
> > switch is closed both capacitors will have v/2 = 500V across them. This can
> > actually be done. But now the energy in the system is half the original
> > value.
> > (1uf*500^2)/2 = 0.125 joules/cap times two caps = 0.250 joules. Were is the
> > other half?"
> >         The rest of the energy was dissipated in resistive losses while
> > the current flowed.  If there were no resistance in the circuit there
> > would be an undamped train of oscillations due to the inductance of
> > the interconnecting leads.  No laws of nature violated.
> > "The classic things I've been taught have me confused with the actual
> > workings of nature. If two charged plates (air dielectric) have a certain
> > charge Q and then a dielectric is inserted between them with a K>1, the
> > voltage should decrease since the charge hasn't changed but the capacitance
> > has increased."
> >         An even simpler experiment is to consider a capacitor (say
> > two spheres) which is charged to some voltage.  If you separate
> > the plates (spheres, etc) the voltage difference between them rises,
> > while if you bring them closer together the voltage difference is
> > reduced.  Conservation of charge holds.  People have built high-
> > voltage electrostatic generators in which a rotating variable
> > capacitor was charged in the high-capacitance state, and then
> > discharged as the capacitance was reduced and the voltage raised.
> > Ed Phillips
> 
> All,
>         If I remember my history correctly, Benjamin Franklin used an
> electro static device that relied on the principal of charged plates.
> This
> device consisted of a jar with a cork lid, and a copper hook protruded
> through the lid with a ball attached to the external end. On the hook
> end
> inside the jar, a peice of copper foil was folded in half and draped
> over
> the hook. The idea being, if a charge was placed on the foil, the two
> halves would repell each other and the foil would open up.
> 
>         The above, It would seam, enforce the idea that in a capacitor the
> charges (i.e.: Electrons and holes) are indeed contained with the
> metallic
> plates. The old world knowledge of our grandfathers still holds true
> today.
> Ed Phillips and all of the others that have pointed this out are
> correct.
> 
> D. Gowin


D.,

Don't confuse coulombic forces with charge.  They are related but not 
exactly the same.  A number of interesting experiments are brought to 
mind, but the actual transfer of charge to the metal occurs in this 
instance from an INSULATOR DIELECTRIC to the metal stucture down into the 
jar where the coulomb forces cause like charges to repel thus the leaves 
separate.  the instant the CHARGE DIELECTRIC ROD IS REMOVED, the leaves 
fall back together (try it!).  

I would be remiss not to tell the hole tale.

The above was charge by contact.

Charge by induction is also possible.  This is really neat.

Take the electroscope and approach with a CHARGED DIELECTRIC 
ROD and the leaves separate as above.  Now with the rod still held 
near the ball, touch the ball only with your other hand or a ground wire. 
 The leaves collapse.  Remove the wire or your hand from the ball.  They 
stay collapsed.  Slowly pull the charged rod away and the air surrounding 
the ball becomes charged to the opposite polarity and the leaves 
magically open up again with no rod there.  The charge is in the air and 
not the metal or leaves.  This charge will slowly leak off in still dry 
air.  A radioactive alpha emitting source held near the Air/Ball 
interface will slowly discharge the air and the leaves will fall much 
more rapidly than in dry air.

This is more of the isolated isotropic capacity discussion than the true 
two plate capacitor scenario.  Real elecricity which can do work can 
actually be pulled off of the metallic rod/ball/leave assembly, but it is 
draining the charge from the air and not from energy stored in or on the 
metal itself.

It is just too bad that we all seemed to get this screwy idea that 
charges can be stored in or on metals.  They Can't!  It is a 
phraseological debacale due to our limited real world abilities to see 
what really happens.  We see real energy apparently coming off the metal 
and so we say it is charged when it is not.  It is merely the real world 
conduit for energy transfer from a seemingly inert dielectric.  We are 
fixated on electrical circuits of metal only.

Richard Hull, TCBOR