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Re: Ludwik Kowalski's textbook touchstone



I am glad that at least one introductory physics textbook recognized
the situation. Thanks for sharing, Thomas.

THOMAS SANDIN wrote:

I've been mostly a lurker for lo these many years, and sometimes
am so swamped that I can't read any of these discussions. However, when I
am able to, I do seriously consider the ideas expressed. For example, in
1995 we included the following in the 9th edition of _University Physics_
(page 784) as a direct result of Ludwik Kowalski's measurements:

No real dielectric is a perfect insulator. Hence there is always
some _leakage current_ between the charged plates of a capacitor with a
dielectric. We tacitly ignored this effect in Section 25-3 when we derived
expressions for the equivalent capacitances of capacitors in series,
Eq. (25-5), and in parallel, Eq. (25-7). But if a leakage current flows
for a long enough time to substantially change the charges from the values
we used to derive Eqs. (25-5) and (25-7), those equations may no longer be
accurate.

Having received no objections, the same words are in the 10th
edition recently published.
Tom Sandin

On Fri, 5 May 2000, Ludwik Kowalski wrote:

And guess what I am looking for when examining a new textbook?
I hope to see a mention (or at least a footnote) on distribution of
equilibrated charges on capacitors in series. Such charges are not
equal, unless leakage resistances happen to be identical. Authors
of two widely used (and often reedited) textbooks saw my demos
and agreed with the obvious conclusion about the inequality of
charges. They promised to address the issue "in the next edition".
That was five five years ago.
Ludwik Kowalski