Re: [Phys-L] Graphite resistivity

[Bernard Cleyet <bernard@cleyet.org>]

> 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.