Oops, I forgot to add one more comment to my last message about the
capacitor result.
Finally, suppose the two plates (with +/-Q/2 on each side) are
insulators so that the charges cannot rearrange when they are brought
near each other. Does this change anything? No (except in the bulk of
each plate as you might expect):
+ + + + + +
===========
+ + + + + +
- - - - - -
===========
- - - - - -
If you now superpose all four fields (+/-s/2)/(2*eps0) due to these
infinite sheet charges, you will get exactly the same answer as if
the plates were conductors.
I wanted to add this, so Ludwik does not get the impression that
charge rearrangement has anything much to do with the story.
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu http://physics.usna.edu/physics/faculty/mungan/