Resistance Through a Hollow Cylinder

[dpeagler]

A hollow cylinder is .012 m long and has an inner radius of 0.005 m and an outer radius of .0175 m. Treat each surface (inner, outer, and the two end faces) as an equipotential surface.

Resistivity of material making the cylinder = 9.68 x 10^-8 Ohm*m

1. At room temperature, what will an ohmmeter read if it is connected between the inner and outer surfaces?

Homework Equations

R=rho/(2pi*L) (ln (b/a))

The Attempt at a Solution

My professor worked this problem out and got 851 Ohms but I cannot figure out how.

Any help is greatly appreciated.

 

[jbsteele]

The answer is 851 Ohms. The formula you need to use is R=rho/(2pi*L) (ln (b/a)), where rho is the resistivity of the material making the cylinder, L is the length of the cylinder, b is the outer radius, and a is the inner radius. Plugging in the given values gives us R=9.68 x 10^-8/(2π(0.012)) ln ((0.0175)/(0.005))=851 Ohms.