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Re: Confused by a derivation.



I think textbook authors, rightly or wrongly, show this both ways...
sometimes within the same text. I am looking at Tipler, 4th Ed. which is
what I am teaching from right now. I am on pages 708 and 709.

Equation 23-25 says E outside the surface of a conductor is sigma/epsilon
(not 2epsilon). At the page turn he talks about contributions from charges
on the other side of the conductor, which is in line with what Bob and Joel
are talking about. But on page 708 he also says... "However, the positive
surface charge density on the outside surface is not disturbed - it is still
uniform - because it is shielded from the cavity by the conductor." That
phrase would seem to voice the other viewpoint.

By quoting a textbook I am not trying to say this view is the right view or
the best view... I am just pointing out that I find this viewpoint expressed
in textbooks that are currently enjoying widespread use.

Bob... can you shed any light on how you got the q1 -q2 - q3 - q4 = 0 that I
asked you about?


Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817