Re: Flat conductors (was I need help).

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Late (I sent only to LK)

I just measured a 10 X 10 cm square (the Ag paint on one pair of
opposite edges) and obtained ~ 7 k ohm.  Then suddenly realized that
ohms / sq. is measured in the interior of a large sheet.  So used Ag
lines one cm separated by one cm in the middle of a 10 X 10 square of
the paper and got ~ 2 K ohm.  A far cry from Pasco's claim.  BTW I
measured using calipers (not cheapies ~ $ 100) and a 50 mill thickness
gauge, 0.14 and 0.142 mm (the thickness gauge has 10 X higher
resolution.), and, therefore, the resistivity is ~ one ohm - m not far
from yours.  However, since graphite is supposed to have a resistivity
of 4 => 11 micro ohm - m, "we" have a problem.  I also measure a #1
(extra soft) pencil "lead"  and obtained ~72 micro ohm -m;  #2  76
.....   And 0.5 mm mechanical lead => ~ six micro-ohm m right in the
middle of the claimed value.


I've measured three (half) equipotentials due to a coupala dots (not
very I slipped and they are ~ 1.8 mm max. - irregular - diameter)
equispaced on the sheet separated by 8 cm.  Even the innermost one is
not circular (4.5 X 6.0 mm).  How do you want me to report it?  A small
file size gif?

bc



Ludwik Kowalski wrote:

> 0.32 ohm*m comes from mu own measurement of R for strip
> of 10 cm between two silver dots. The strip thickness, 0.013
> mm was measured with a micrometer.
>
> Bernard Cleyet wrote:
>
> > Oh oh  I must be missing something.  My references give
> > carbon's resistivity as about 10 micro-ohm -m
> >
> > My Pasco instruction sheet just gives the resistance of the
> > paper (5 => 20 ohm per square).
>
> I was reading Carl's last year message and it occurred to me
> that his setup has one advantage; it allows rho to be changed
> gradually by several orders of magnitude (by changing the
> concentration). It would be interesting to see the line pattern
> from this setup for two small cylinders (or wires) immersed
> in the electrolyte and separated by 10 cm, as in the geometry
> chosen for Pasco paper. What would the effect of rho be?
> Ludwik Kowalski