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Re: [Phys-L] Graphite resistivity



John,
In the past I've measured V, and I with the dmm probes at different
locations along the rod of pencil lead while also measuring L and A of the
rod of pencil lead. We plot the data to get R. We plot other data to get
rho.
In a separate lab, they determine the thickness of the drawn line.
There are additional activities present in the packet from general atomics,
but I was checking in the soft lead for these labs.
Thanks for your help.
Have a good one.
Paul.
On Mar 4, 2016 3:58 PM, "John Denker" <jsd@av8n.com> wrote:

On 03/04/2016 02:23 PM, Lulai, Paul wrote:

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?

I surmise that the procedure involves /drawing/ with the
pencils. This is in quite a different category from
experiments that measure the R of the "lead" while still
in rod form.

For this application you probably want all the conductivity
you can get.

There are a bazillion kinds of "art pencil".
Some are very very soft (compared to the generic pencils they
sell at the supermarket). That means more conductivity.

Some of the really dark art pencils use charcoal black, which
is very soft and very black. In contrast, the stuff they put
in ordinary pencils has a great deal of binder: clay, wax,
glue, and whatnot.

=======

Possibly tangentially relevant: Another way of writing with
carbon is India ink. You can get some seriously dark lines
this way.

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