# Resistance of a holow sphere

1. Sep 21, 2009

### lockedup

1. The problem statement, all variables and given/known data
Determine a formula for the total resistance of a spherical shell made of material whose conductivity is $$\sigma$$ and whose inner and outer radii are r1 and r2. Assume the current flows radially outward.

2. Relevant equations
$$\sigma$$ = 1/$$\rho$$

R = ($$\rho$$*l)/A

3. The attempt at a solutionSince the current is moving outward, l (length) is going to be the difference of the radii. How do I account for the changing surface area?

The solution is (r1 - r2)/(4$$\pi$$*$$\sigma$$*r1*r2)

EDIT: *facepalm* I spelled hollow wrong...