RE: Capacitors store atomic energy! ;)

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

With trepidation, I still continue to enter the fray.

> But (1) has unwanted implications.  Should we say that a neutral hydrogen
> atom, when its electron is pumped up from the ground state, has "stored
> some charge"?  But the atom's still neutral!  A particular configuration
> of charge has been stored, but a configuration of charge is not "electric
> charge".  When I stretch a rubber band, I have stored a particular
> configuration of rubber, but I have not injected any rubber into it.  When
> a hydrogen atom absorbs a photon, we do not say that it has absorbed
> charge, and we should maintain the same consistent treatment for (2-plate)
> capacitors.

As I said, it was a trivial reason; emphasizing the fact that neutral does 
not mean no charge.

> In addition, if we focus always on the charge phenomena regarding
> capacitors, we may forget to describe capacitors from another standpoint:
> capacitors store energy, they are "charged" with EM energy, they release
> EM energy during "discharge", and EM energy is a very different animal
> than electric charge.  Insisting that capacitors store charge can confound
> the roles of energy and charge in the minds of students.  (This certainly
> is what happened to me as a student.)  It's analogous to stating that
> springs store steel.  Very confusing.  Springs store energy in a
> particular *configuration* of steel, but a configuration of steel is not
> steel.  When a spring is "charged" or compressed, no steel is injected
> into it, but energy is.  When a capacitor is "charged", no charge is
> injected into it, but energy is.  At least springs are visible, so some
> sorts of misconception are impossible.  Not so with invisible charge-flow
> and invisible EM energy.

By EM energy, I assume you mean the idea of energy density contained in an 
electric field; which is what I will mean below by "EM energy".

1) I didn't say anything about where my focus is regarding the charging of 
capacitors.  In my classes I do emphasize the idea of energy storage and I 
am very careful to operationally define what charging a capacitor means.

2) Everything in this item should be interpreted under the constraints of 
Maxwell theory in *electrostatic* situations.

In electrostatic situations, energy and charge configuration should be 
confounded as they are equivalent descriptions.  One can compute the total 
electrostatic potential energy by integrating energy density in E-field 
(integrating E field squared) or by directily calculating (integrating) 
coulomb potential of pair-wise interaction between the charges.  It is 
equally valid to regard the energy stored as residing in the E field or in 
the geometric configuration of charges.

3) BTW I never use the bucket analogy for capacitors; probably for all the 
reasons you allude to.

Joel