# Resistivity

Question:

I know that the
resistivity of an insulating paper is 10x10

^{9} Wm.

But how do I set up an experiment to find out the resistivity or
to prove it is correct or not ?

## Answer:

The paper that you have
apparently has a resistivity of 10x10

^{9}Wm or 10000
M

Wm.

Lets also assume that you have a digital meter
that will enable you to measure a resistance of around 10 M

W.
(this is quite normal for the meters available in Britain now).

The connection
between resistance and resistivity is:

Resistance = resistivity x length/area.

Now
if the resistance is 10

^{7} W, the resistivity 10

^{10} Wm and the paper is 10

^{-4} m thick then you would need a
piece 0.1 square metres in area with contacts taped to the two faces.
Possible!

Alternatively using a pico ammeter (currents as low as 10

^{-10} A.
You could tape the contacts to the two faces and simply measure the current passing
through the paper with a variety of applied voltages.

So for a piece of your paper 1
cm square with a resistance of 10

^{10}W the current for
a 12V input would be 12/10

^{10} = 1.2 nA (12x10

^{-10} A) – easily within the
range of the meter I have looked at.