Re: electric bulges

["Donald E. Simanek" <dsimanek@eagle.lhup.edu>]

On Fri, 7 Mar 1997 kowalskil@alpha.montclair.edu wrote:

> David Bowman's phrase, " ... any response at the astronomonical driving
> frequency.. " prompted me to think that electricity can perhaps provide
> some analogies for tides. Consider a negatively charged metallic sphere.
> The uniformly distributed electrons represent an "ocean". You bring a
> positive charge into its vicinity and a single "bulge" of electrons is 
> created. Bring a third positive charge into this region and you have a 
> system "driven" by two sources. Is it a useful analogy?
>
> Or consider a metallic sphere which is initially neutral. We can create
> two bulges (+ and -) by electrostaitic induction. Nothing profound, just
> trying to share my thoughts.
>                                             Ludwik Kowalski
>
> > He ends by saying "...and devote my time to more productive things."
>
> A common dilemma. But messages which promote thinking ARE VERY productive.

One problem: gravitation involves masses, which come in only one sign.
Charges come in both signs + and - and the bodies we usually talk about
have both signs of charge in abundance, with only a slight disparity
between them, when the body is charged.

Now if you imagine a spherical blob of charge of only *one* sign in an
external electric inhomogenous field (not constant in strength or
direction) then the initially spherical blob of charge will distort into
an elongated blob, with *two* tidal bulges, just as in the case of an
elastic massive body in an inhomogenous gravitational field. Indeed this
is a standard homework problem in upper level electricity and magnetism
courses.

	-- Donald

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Dr. Donald E. Simanek                            Office: 717-893-2079
Prof. of Physics                    Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745          CIS: 73147,2166 
Home page: http://www.lhup.edu/~dsimanek            FAX: 717-893-2047
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