Re: [Phys-L] Graphite resistivity

[Todd Pedlar <pedlto01@luther.edu>]

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

On Fri, Mar 4, 2016 at 3:23 PM, Lulai, Paul <plulai@stanthony.k12.mn.us>
wrote:

> Hello.
> I am getting ready to do a resistivity lab that I've done for a decade but
> I ran into a problem. The art pencils that I've been using are gone. They
> apparently vaporized along with my packet of materials from an old aapt
> workshop a decade or more ago.
> I remember that art pencils were better because...
> I don't remember...
> I am tempted to pick up softer leaded pencils so the lead would get into
> the cracks of the paper.
> Does anyone have a quick recommendation?
> Thanks for your help.
> Paul.
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-- 
Todd K. Pedlar
Associate Professor of Physics
Luther College, Decorah, IA
pedlto01@luther.edu