Resistance of a Cylinder

In this formula, length and area are geometric properties of the cylinder; the ratio L/A has dimensions of reciprocal length. The Greek symbol "rho" above stands for resistivity, a property of the material making up the cylinder, usually reported in ohm-cm. The separation of the dependence of a physical quantity into geometric and material parts is typical.

Note that the resistivity determined for Play-Doh ranged from 10 to 20 ohm-cm, depending on the color. Compare this with a good conductor: copper has a resistivity of 0.000002 ohm-cm. Thus 10 cm of Play-Doh has the same resistance as one million meters of copper wire of the same diameter!