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Re: Flat conductors (was I need help).



1) Correction: the current at 300 volts was 11 mA, not 5.5 mA,
as posted about two hours ago. This is probably irrelevant, as
far our problem is concerned. But it shows that the new sheet
has exactly the same R as the one I used before. The sheet is
very linear (in terms of the mA versus volts) up to at least
300 V.

2) There is one question I keep asking but nobody answers.
Is it because nobody knows what to say or because I did
not make myself clear? Perhaps the question is silly but I
would like to know why. (Actually David did answer on
February 24 but his explanation was above me.) Let me
try one more time; perhaps it will generate a clearer
explanation. I am probably not the only one who was not
able to understand David's vanishing tensor, etc.

In air, or on an acetate sheet, two small silver dots separated
by a distance much larger than their diameters, would produce
a field of a 3D dipole (except very close to circles). The electric
field lines would not be confined to a single 2D plane because
all meridian planes are identical. An electric current, of the
order of pA would be flowing, more or less along the E lines
in the 3D space.

If the resistance of the acetate sheet were progressively lowered
then more and more current would flow through the sheet and
less and less above and below it. Eventually we would have a
flat conductor carrying practically all the electric current. The
distribution of E is no longer like for a 3D dipole, it is like
that of a 2D dipole (two infinitely long cylinders perpendicular
to the 2D sheet). It looks like if the electric current, in process
of changing its path, also changed the configuration of E. The
current is saying to the field "I become 2D and you must do
the same." Why is it so?

The only way I can rationalize this is to assume that static
surface charges associated with the steady state flow are
responsible for what really happens. How else can this be
explained? Static charges, by the way, were discussed here
recently in a thread whose name was "Chabay/Sherwood."
Ludwik Kowalskil