thomas malloy wrote:
...
I thought that grounding was part of the definition of a Faraday Cage.
Not really. The important thing about a Faraday cage is that inside it
you cannot tell anything about electric fields or electric potentials
that exist outside. You can't tell (in theory at least) whether the
cage you are in is grounded, or sitting at 100kV, or on the top of a
Tesla coil and being oscillated plus and minus to many megavolts.
In this Ron's case however there is an "ground" wire entering the cage
and who knows what potential difference exists between the cage and the
wire entering it until he measures it. This is the important thing - it
doesn't matter whether either or neither are grounded - it just matters
what is the AC and DC difference in potential between the wire entering
and a well constructed cage.
As Jed pointed out, a pair of heavy iron frying pans might make a superb
Faraday cage. If you calculate or look up the skin depth from
http://en.wikipedia.org/wiki/Skin_depth, then at the frequency and
thickness obtained the oscillating field is reduced by a factor of 1/e
in comparison to the situation without a shield. At twice this
thickness, the field is reduced by a factor of 1/e^2, and so on.
Robin van Spaandonk wrote:
> ... Note that Tesla lit light bulbs 25 miles away, with no wires,
> using only the ground as common medium. ...
As I understand it there were two conductors - the earth and the
ionosphere. The ionosphere was coupled to capacitively using a tall
mast and high frequency and voltage oscillations. There may have been
some ionospheric resonance involved also, but the whole process is not
something that is really known about and AFAIK has never been done since.
