Re: Capacitor energy experiment

[Michael Burns-Kaurin <mburns-k@SPELMAN.EDU>]

I will try asking Bob's question in a different way.  Suppose I have two 1
F capacitors, each with potential difference 1 V.  What physical difference
between the capacitors makes one of them "store" 1 J while the other
"stores" 0.5 J?

Michael Burns-Kaurin
Spelman College





                      David Rutherford
                      <drutherford@SOFT        To:       PHYS-L@lists.nau.edu
                      COM.NET>                 cc:
                      Sent by: Forum           Subject:  Re: Capacitor energy experiment
                      for Physics
                      Educators
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                      02/12/2003 08:20
                      PM
                      Please respond to
                      Forum for Physics
                      Educators






Bob LaMontagne wrote:
> David Rutherford wrote:
>
> > Bob LaMontagne wrote:
> > > For the capacitor, excluding mechanical deformation energy losses,
etc., the
> > > energy is in the field - the electrons cannot store energy internally
- they
> > > are point objects. Others on the list have calculated the thermal KE
> > > associated with the electrons themselves and it was  negligible
compared to
> > > 1/2 CV^2.
> >
> > I'm not interested in what list members may have calculated;
> > calculations cannot be used as evidence. Obviously the energy
associated
> > with the heat dissipated by the resistor, during charging, is not
> > negligible, it is 1/2 CV^2 (I'm assuming it has actually been
measured).
> >
>
> David - If you reread what I said - I'm not refering to the resistor at
all. I am
> simply challenging you - since your accepted an energy of 1/2 CV^2 in the
> capacitor in your recent posting - to show how an identical capacitor
with the
> same charge (and therefore field) could have any other value for it's
energy even
> if it were charged without a resistor, i.e. from another capacitor - or
an
> inductor in a switched circuit - or any of the other proposals that
people have
> brought up on this list.

I _only_ agree that the energy in the capacitor is 1/2 CV^2 if the
energy dissipated during the charging of the capacitor is 1/2 CV^2.
Otherwise I _don't_ agree.

> Again, I'm curious only about your claimed value for the
> energy stored in the capacitor - even after it has been disconnected from
the
> charging circuit and removed far from its location.

It depends on how much energy was dissipated during the charging of the
capacitor.

--
Dave Rutherford
"New Transformation Equations and the Electric Field Four-vector"
http://www.softcom.net/users/der555/newtransform.pdf

Applications:
"4/3 Problem Resolution"
http://www.softcom.net/users/der555/elecmass.pdf
"Action-reaction Paradox Resolution"
http://www.softcom.net/users/der555/actreact.pdf
"Energy Density Correction"
http://www.softcom.net/users/der555/enerdens.pdf
"Proposed Quantum Mechanical Connection"
 http://www.softcom.net/users/der555/quantum.pdf