# Finding the thickness of graphite in a circuit

janegoldberg

In class, I "drew a circuit" with a pencil. When the LED was moderately bright about 9mA was flowing and so (since I was using a 9V battery), the resistance was about 1 kΩΩ.
At this point, the distance 𝐿L between the battery and the LED was about 10 cm and the width of the pencil line was about 1cm. If the conductivity of the graphite was about 𝜎𝐶≈1000σC≈1000S/m , estimate the thickness (i.e. height above the paper) of the line I drew.