Re: Why does electrostatic attraction in water decrease?

["John S. Denker" <jsd@MONMOUTH.COM>]

Pentcho Valev wrote:
> I cannot do the experiment, for many reasons.

Really?  What reasons?  How hard did you try?


> However there is another instructive
> thought experiment
....
> A) The net work gained in steps 1 and 3 is done at the expense of heat absorbed from
> the surroundings. If so, the second law is of course violated.

I see no reason to believe this would happen.

> B) The net work gained in steps 1 and 3 is done at the expense of WORK THE OPERATOR
> SPENDS IN STEPS 2 and 4. This saves the second law, but is somewhat
> counterintuitive.

It seems perfectly intuitive to me.

> Roughly speaking, this means that in step 4, as the operator lifts
> the capacitor, the capacitor is MUCH HEAVIER than in step 2 when the operator lets
> it down.

Not "MUCH" heavier, just heavier enough.

Elementary electrostatics predicts exactly this.
You can do the calculation on a 2-inch square piece of
paper;  why not do it yourself?

Hint:  Do the analysis and constant charge Q rather than
constant voltage V, so you don't need to worry about work
done by whatever is holding V fixed.  The electrostatic
energy is a potential, and is a function of two variables:
the gap g and the area A.  The force is the gradient of
this potential.  There's nothing surprising and nothing
tricky about it.