A thick-walled, conducting spherical shell has charge q = +10 mC, inner radius R1 = 10cm, and outer radius R2 = 50 cm. A point charge Q = -20 mC is located at the center of the shell.
Describe the the charge distribution in the shell.
2. Given answer
+20 mC on the inner surface; zero charge in the interior of the sphere; -10 mC on the outer surface.
The Attempt at a Solution
I know that there can be no net charge with a gaussian surface drawn inside a conductor, so in order to balance out the point charge, there must be +20 mC of charge on the inner surface, and then there should be a net charge of +10 mC on the whole sphere, so there would be +10 mC on the outer surface. I don't understand why the charge in the interior is zero; shouldn't it be -20 mC because of the point charge?