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Re: Surface charge distribution



Jack,
The two concentric, uniform spherical charge distributions along with the
single off-center point charge cannot result in the spherical equipotential
surface (or volume) where the conductor is. The inner charge distribution
must be asymmetric.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Jack Uretsky" <jlu@HEP.ANL.GOV>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, December 04, 2002 7:27 PM
Subject: Re: Surface charge distribution


| Hi-
| The only response that I saw just gave an answer without an
| explanation. I suggest that the reverse would be a better practice.
| A charge is placed off-center inside a spherical conducting shell.
| Find the field outside of the shell.
| The issue is: what is the meaning here of (perfectly) "conducting
| shell"?
|
| What is meant is that that the positive and negative charges in the shell
| are free to position themselves so that no currents flow in the shell.
| This requires that the positive charges all get pulled to the inner
| surface, the negative charges are pushed to the outer surface, and the
| charges distribute themselves uniformly - that's the key, uniformly - over
| each surface. Uniformity is required to avoid currents running along the
| surface.
| Note that a spherical Gaussian surface that lies completely within
| the shell (that is, between the inner and outer surfaces of the shell) is
| in a field-free region. The net charge enclosed is zero.
| A similar surface outside of the outer surface of the shell must
| then enclose a net charge equal to the charge that was place inside (of
| the inner surface) of the shell.
| Regards,
| Jack
|
| On Tue, 3 Dec 2002, Fakhruddin, Hasanbhai wrote:
|
| > Hello Everyone!
| >
| > Need help with the following conceptual problem:
| >
| > A conducting shell is initially neutral. A point charge +q is placed
| > OFF CENTER inside the cavity. Is the charge induced on its outer
| > surface symmetric or asymmetric? =20
| >
| > Thanks,=20
| >
| > Hasan Fakhruddin
| > Instructor of Physics
| > The Indiana Academy for Science, Mathematics, and Humanities
| > BSU
| > Muncie, IN 47306
| > E-mail: hfakhrud@bsu.edu
| >
|
| --
| "What did Barrow's lectures contain? Bourbaki writes with some
| scorn that in his book in a hundred pages of the text there are about 180
| drawings. (Concerning Bourbaki's books it can be said that in a thousand
| pages there is not one drawing, and it is not at all clear which is
| worse.)"
| V. I. Arnol'd in
| Huygens & Barrow, Newton & Hooke


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