Spherical Capacitor: Calculating Capacitance in pF

[professordad]

Homework Statement

A spherical capacitor consists of a spherical conducting shell charge $-Q$ concentric with a smaller conducting sphere of radius $4.0$ cm and charge $Q$. The larger conducting shell has inner and outer radii of $11.0$ cm and $13.0$ cm, respectively. What is the capacitance of the system in pF?

Homework Equations

$C = \frac{Q}{\Delta V}$

The Attempt at a Solution

I don't know what to do when the outer shell has a thickness. I know that when it doesn't have a thickness you would do
$-\int_{r_1}^{r_2} kQ\frac{dr}{r^2}$
where $r_1$ and $r_2$ are the inner and outer radii, respectively. But here what do you do for $r_2$?

Thanks.

 

[Tanya Sharma]

How would -Q be distributed on the outer shell ?