Subject:  Re Faraday's cage
Date:     Tue, 15 Jul 1997 093217 -0500 (CDT)
From:     "Peter Heindl" <IFG-sa@netactive.co.za>
To:       Multiple recipients of list <emf-l@mail.llion.org>
--------------------------------------------------

Hello there,

Haldun is right, a Faraday cage does not have to be earthed, a car standing
on rubber tyres, in dry weather or in rain, is a perfect Faraday cage! Let
lightning strike! - Your antenna and car radio, might however not be so
lucky.

BTW, did you know that for IONS contrete walls also work similar to a
FARADAY
CAGE? This could be harmful to your health, too. It causes the so called
CONCRETE SYNDROME, as described in a German book I have!
- Sorry no time for translation right now! - Remind me at a later stage in
about 2 months or so, when my urgent work should be finished.

Best regards.
   Peter

----------
> From: Haldun Ozaktas 
> To: Multiple recipients of list 
> Subject: Re: Faraday's cage
> Date: 09 July 1997 15:43
>
>
> > 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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