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Re: [Phys-L] Graphite resistivity



Last month I went all over the city and county looking for a store to buy
ribbons for my old typewriter and my ancient one.

Nobody in any store knew what I was talking about.

Then I asked for india ink, to recharge the old ribbons,
and that was also futile.



On Sat, Mar 5, 2016 at 6:06 PM, Bernard Cleyet <bernard@cleyet.org> wrote:


On 2016, Mar 04, , at 13:30, Todd Pedlar <pedlto01@luther.edu> wrote:

I had a pretty good experience a couple weeks ago using regular 0.7 and
0.5mm HB mechanical pencil leads (actually it's great if you can also get
0.9 and 1.3 from the same company). Simply studying potential drop vs.
current for various lengths and for the different diameters enables a
nice
verification of the relation between resistance, resistivity, length, and
cross-section. Equipment used: DC power supply, banana cables w/aligator
clip ends, micrometer for length and diameter measurements, DVM. Really
quite straightforward to vary the length of the 'resistor' and my
students
did V vs. I plots for 8-10 lengths each, and for all four lead sizes.
Really nice and reproducible results.

TKP


I thought the point of using graphite pencil lead was their negative
resistance. Can one simply Joule heat it and find the R using I and EMF
while heating? the wood case acts as an insulator.

bc notes some leads show diamagnetism also.
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