Subject:  Re Faraday's cage
Date:     Wed, 9 Jul 1997 084515 -0500 (CDT)
From:     haldun@ee.bilkent.edu.tr (Haldun Ozaktas)
To:       Multiple recipients of list <emf-l@mail.llion.org>
--------------------------------------------------

> For the Faradys cage to work properly is does NOT, repeat not, need to be
> "grounded". Ground, earth or soil has nothing to do with Faradys cage.
> What the cage does is to equalize the potential differences at all points
at
> the surface (boundary) of a contained space. Inside that space there is no
> potential differences and thus no electric field.
>
> Clas Tegenfeldt       ,,,

Another way of putting it is as follows:

1) The E-field inside a conductive enclosure will always be zero,
even if not grounded. ("Proof"= step1: The E-field inside the metal must
be zero since if not, charge movement will continue until it is
and the potential everywhere on the conductor is the same. step2: If
one has a closed regions whose boundary is at uniform identical
potential, then the inside is also at the uniform potential by the
uniqueness theorem, and there is no field inside.

2) However, to shield yourself from a source by using a conducting
finite barrier, that barrier must be grounded to be able to attract
from earth the charges to terminate the E-field lines.
(Example: grounded conducting monitor shields)

Haldun

________________________________________________________________________
Haldun M. Ozaktas
Bilkent University                      (90) (312) 266 40 00 / 1619
Department of Electrical Engineering    (90) (312) 266 43 07 (secretary)
TR-06533 Bilkent, Ankara, Turkey        (90) (312) 266 41 26 (fax)
www.ee.bilkent.edu.tr/~haldun           haldun@ee.bilkent.edu.tr


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