Re: Electrostatic shielding

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

If the cage is a grounded conductor, then since the field in the
conductor at equilbrium must be zero, charge will move from ground to
the inside surface of the conductor.  Thus the field outside the
conductor will always be zero.  If the conductor isn't grounded, then
the result will be an induced charge on the outside of the conductor and
the field outside the conductor will not be zero.  So for this sort of
shielding, the conductor needs to be grounded.

Shielding the inside from the outside does not require grounding since
the field inside depends on the enclosed charge, and in this model there
isn't any.

cheers

joe

On Wed, 31 Jan 2001, Lemmerhirt, Fred wrote:

> Can anyone share a reference to a favorite explanation of "electrostatic
> shielding" (at the level of calculus-based introductory physics)?
>
> Also, in the process of seeking a satisfactory explanation, I tried A. D.
> Moore's little book on electrostatics.  In Moore's discussion of Faraday's
> cage experiment, he says:
>
> " . . . .  He proved that any electric field he might set up outside of the
> cage had no effect whatever on detection instruments placed inside.
> Likewise, fields set up inside had no effect outside."
>
> Is that last statement correct?  (Maybe the answer depends on whether the
> cage is "grounded" or isolated?)
> ______________________________________
> Fred Lemmerhirt
> Waubonsee Community College
> Sugar Grove, Illinois
> flemmerhirt@mail.wcc.cc.il.us <mailto:flemmerhirt@mail.wcc.cc.il.us>
> http://chat.wcc.cc.il.us/~flemmerh/physics.html
> <http://chat.wcc.cc.il.us/~flemmerh/physics.html>