Re: [Phys-l] RC Discharge

[John Denker <jsd@av8n.com>]

Edmiston, Mike wrote:

[A}
> positive charge on one plate,
> negative charge of equal magnitude on the other plate ... 
> I suspect this is what most students think of
> when thinking of a charged capacitor.

Well, that's what we *want* them to think of, but actually it is
a source of some nontrivial confusion, since:

[B]
>  we can also remove, say, negative charge from each plate, such that
> both plates end up with positive net charge.  

Indeed we can.

=========

This is a classic case of the same word being used with two
meanings that are both similar enough and different enough to
cause maximum confusion.

 Meaning [A] is used in vernacular expressions such as charging
  a battery and charging a capacitor, and is pretty much standard
  in electrical engineering.  It applies to a scenario where
  Kirchhoff's "law" is upheld.

 Meaning [B] corresponds to the fundamental physics view of what
  "charge" is.  It applies to a scenario where Kirchhoff's "law" is
  violated.

When necessary, I use the term "bicharge" to describe the quantity
in scenario [A], to distinguish it from the plain old charge in
scenario [B].  Carrying this idea to the next step would require
speaking of bicharging a battery, and then disbicharging it,
which I admit sounds a bit awkward ... but it makes the point.