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I think this is worth sharing with the list. Give the reference
but do not assume people have access to this book. I suggest
you write the formula and describe how you used it to get
the R of the infinite size sheet of a conductive film of known
thickness. Show numerical calculation for Pasco sheets.
Outlining the derivation is likely to be appreciated by many,
provided it is explained in simple terms.
Ludwik.
Bernard Cleyet wrote:
Damn! I threw out that scrap of paper and must begin again.
I claimed ~ 0.1 ohm you got 0.06 . My calc. remembers entries, so I pushed
the key a jillion times and found more exactly your number 0.0587.....
with conductivity 1/ 0.32 instead of 1 E+5 mho/m and thickness 0.013
instead of 0.2 mm (your revised thickness is because you scraped off the
aquadag and found the diff. between both and the paper only?)
28.9 k ohm
bc
P.s. It's Ln (separation / radius)
Ludwik Kowalski wrote:
You are probably referring to what is on page 42. Note that
in my case a=b (figure 1.29). If I use your formula then
R=0 because ln(b/a)=ln(1)=0. You probably made a typing
error, or something of that kind. My sigma was 1/0.32
and the sheet thickness was 0.013 mm. (What R do you
get after correcting the mistake?)
Ludwik
Bernard Cleyet wrote:
Correct. However, the method is applicable to 2-D.
Find the capacitance per unit length of two cylinders (parallel of
separation l) replace kappa sub zero with the conductivity / unit area
and invert.
e.g. resistance between two coaxial cylinders: C = (2 Pi kappa * l) /
[ ln (b/a)]; R = ln (b/a) / (2 Pi * sigma * l)
where sigma is the volume conductivity
I have all ready to mail. I think you'll appreciate it any way.
bc
P.s. there's another method: a square mesh of resistors with the
number of resistors increased => in the limit to area conductivity.
Ludwik Kowalski wrote:
Hi again, Bernard:
It occurred to me that perhaps the R formula on page 102 refers
to a 3-dimentional system (current flowing between two spheres
and not between two flat electrodes in a conducting sheet). This
would explain why R is nearly 200 smaller than what was
calculated with Bowman's formula. Verify this before sending
me anything. I am interested in 2-dim only, as you know.
Ludwik