Re: Why does electrostatic attraction in water decrease?

[Pentcho Valev <pvalev@BAS.BG>]

"John S. Denker" wrote:

> Some additional remarks:
>
> 1) I haven't seen the exact phrasing of Panofsky's
> example.  Conflicting versions have been posted.
>
> 2) I can nevertheless guess and probably come
> pretty close to fingering the underlying physics.
> There are a zillion problems of this sort, all
> rather similar.
>
> a) You can figure out what the answer is pretty easily
> using energy considerations.
>
> b) When people start asking about details of the
> mechanism, all the details reside in the fringing
> fields.
>
> In this case, to see the role of fringing fields,
> punch a small hole right in the middle of one of the
> capacitor plates.  Does the high-pressure water
> between the plates leak out through the hole?  No.

How do you know? Please see fig. 6-7 on p. 112 in Panofsky. A capacitor
with vertical plates is only partially immersed into a pull of liquid,
and the liquid inside the capacitor has risen high above the surface of
the pull. Now punch a hole in one of the capacitor plates, above the
surface of the pull but below the surface of the liquid inside the
capacitor. Will the liquid leak out through the hole? I would be very
surprised if it does not.

I am afraid the discussion goes directly to the second law of
thermodynamics - a topic I hate because it always generates personal
attacks but never science. Perhaps a calmer problem is the following. Is
it justified to identify the dielectric constant that one places in the
Coulomb law, for two charges immersed in a liquid dielectric, with the
dielectric constant participating in the expression for the voltage of a
capacitor with a box filled with the same liquid dielectric between the
plates? If Panofsky's pressure does exist, the two quantities reflect
entirely different physical events.

Pentcho