Re: Flat conductors (was I need help).

[kowalskil <kowalskil@MAIL.MONTCLAIR.EDU>]

Another diabolic trap? Probably not. What do you think?

I just realized, while comparing my calculation of rho with
that of Bernard, that I confused mm with centimeters. The
paper thickness should have been 0.013 cm, not 0.013 mm.
Consequently the value of rho was not 0.32 but 3.2 ohm*m.
To check this I remeasured rho using the 26 cm strip of 1 cm
width and found rho=3.3 ohm*m. I am glad that nothing
discussed so far depended on the actual value of rho. But,
according to Larry Woolf:

> The room temperature electrical resistivity of carbons and
> graphites can vary between 10^-6 ohm-m and 10^-2 ohm-m
> depending on heat treatment temperature. (See: Ch2. "The
> Electronic Transport Properties of Graphite, Diamond,
> Carbon, and Related Materials" by Ian Spain, ib Chemistry
> and Physics of Carbon, Vol 16, ed. by P. L. Walker and
> P. A. Thrower.

Hmm; that is puzzling. The only way to consolidate the
situation is to assume that the so-called "carbon impregnated"
paper is not uniform and that the conducting layer is much
thinner than the paper. To verify this I measured the resistance
through the paper rather than along the paper surface. I painted
silver dots facing each other through the paper; their diameters
were 4 mm. Then I measured R; it turned out to be 1130 ohms.
For the uniformly impregnated paper the R, for that arrangement,
would be 34 ohms, not 1130 ohms. It is thus clear that what I
was reporting was an apparent rho; the real rho must be much
smaller than 3.3 ohm*m..

Does anybody knows what the carbon solution consists of before
it is used to impregnate Pasco paper. Is this paper manufactured
for students only or for some other uses as well? It is remarkable
that different sheets of the non uniform paper yield practically
identical results. The industrial process seems to be very well
controlled. But I never compared sheets from another batch.
Ludwik Kowalski