Re: Non-conservative forces in a liquid dielectric

[Pentcho Valev <pvalev@BAS.BG>]

Carl Mungan wrote:

> Pentcho wrote:
>
> > Perhaps I should add something about non-conservative forces.
> > Textbooks usually define a
> > conservative force as one which, as you do work against it
> > (isothermally), keeps the energy
> > and does not dissipate it as heat. In contrast, as you do work
> > against a non-conservative
> > force, the energy is dissipated as heat. Then always friction is
> > refered to so that many
> > scientists do not suspect that there could be non-conservative
> > forces other than friction.
>
> I'm not very happy with these definitions.
> I would prefer to replace "heat" with "thermal energy" and take your
> 3rd sentence as defining a "dissipative" force rather than a
> "nonconservative" one.

The problem is much more serious than that. In 1962, two renowned
authors write in a renowned textbook:

"A factor 1/k is frequently included in the expression for Coulomb's law
to indicate this decrease in force. The physical significance of this
reduction of force, which is required by energy considerations, is often
somewhat mysterious. It is difficult to see on the basis of a field
theory why the interaction between two charges should be dependent upon
the nature or condition of the intervening material, and therefore the
inclusion of an extra factor 1/k in Coulomb's law lacks a physical
explanation" (W. Panofsky, M. Phillips, CLASSICAL ELECTRICITY AND
MAGNETISM, Addison-Wesley, Reading, Massachusetts (1962) p. 114)

The authors do not call k "dielectric constant" and their interpretation
of the effect leads to the following conclusion: The decrease of the
force of attraction between two capacitor plates immersed in a liquid
dielectric, mysterious or not, surely has NOTHING TO DO with the
decrease in voltage between the plates. The former effect is due to the
mysterious pressure developing between the plates and pushing them apart
whereas the latter can easily be explained in terms of polarization.
     For the next 40 years, no physics teacher has found it suitable to
ask him/herself: If Panofsky and Phillips are right and the two effects
are essentially different, why don't I explain this to students? Why do
I mislead them so fatally by introducing the same quantitative measure
(the dielectric constant) for two essentially different effects? As
Panofsky's pressure does work (e.g. pushes the plates apart), at the
expense of what energy is this work done? Since this could not be the
electrical potential (the pressure counteracts it), could the energy
source be heat absorbed from the surroundings? In what other cases do
electrochemical systems absorb heat and convert it into work? How about
batteries? They are known to convert CHEMICAL energy into work, but
could that be just one of the numerous illusions in physics education?
The simplest electrochemical cell

Zn2+ (high concentration),  Zn II  Zn,  Zn2+ (low concentration)

surely involves NO CHEMICAL REACTION and yet it could do work. At the
expense of what energy?
     Note that the problems raised concern material taught to freshmen
and college students. Before resolving these problems it would be
premature to argue which force is conservative and which is not so
conservative.

Pentcho