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Re: Flat conductors



Here's my R(t) data from ca. 20020302 for a square of Pasco paper with
an opposite pair of Ag "electrodes."

The first column is the temp. (deg. F) the second the inverse of the
resistance * 10000.

It fits the eq. 1 / R = a * (1 - exp(-b * t)) + c

Since I don't have values for SD, I can't supply a Chi-square. The
temp. resolution is ~ 3 F deg.; the resistance 0.01 k ohm. I found
the paper very sensitive to humidity. Only data taken above RT was
valid (repeatable and internally consistent)


260 2049
265 2045
260 2045
255 2041
250 2035
245 2041
240 2030
230 2024
220 2016
210 2010
200 2002
190 1992
180 1984
170 1973
160 1961
150 1949
140 1931
135 1923
130 1912
125 1913
120 1913
114 1866
110 1856
105 1839
104 1832
100 1815
92 1759
90 1753
90 1748
85 1698
80 1643
64 1516

bc





Ludwik Kowalski wrote:

The temperature coefficient of resistivity for carbon is known
to be negative. Pasco paper can be used to demonstrate this.
Here are my data showing that R (V/mA) goes down when
the temperature increases.

volts mA temp
============================
50 19.1 room
75 30.0 slightly warmer
100 42.5 clearly warmer
150 70.5 very hot
200 99.9 too hot to hold

As you can see, the temperatures were not measured. I waited
several minute after each change of voltage (till the current
stopped changing). I was afraid that the sheet might burst
above 200 V. It would not be hard to measure T but I did
not do it. Worth sharing? I hope so. My resistor was defined
by two concentric circles silver-painted on Pasco paper. The
radii were 1.5 cm and 6 cm. I will tell you more about this
circular geometry in another message.
Ludwik Kowalski