Subject: Re Faraday's cage
Date: Tue, 15 Jul 1997 092605 -0500 (CDT)
From: Clas Tegenfeldt <tegen@bemi.se>
To: Multiple recipients of list <emf-l@mail.llion.org>
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At 08:43 1997-07-09 -0500, you wrote:
>> 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.
>
>Another way of putting it is as follows:
snip...
>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)
You talk about generalized shields here, and even they do NOT need "earth"
to
work! What we are talking about is equalisation of charge distribution.
The idea of shielding electric fields from eg. monitors by using a earth
wire
works for LOW frequencies but will not work for high frequencies (above some
tens of megahertz). I would again like to stress that earth has no
special property (okey, we stand on it, but what the heck) but anything that
has a large amount of free electrones will do. Why we use the earth wire is
because it /also/ is connected to the electrical system as a reference. The
only reason that reference also is connected to a grounding rod into the
soil
is because we want protection against lightning! OK?
Clas Tegenfeldt ,,,
(o o)
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