Electric Field inside a metal sphere

[Squall]

Homework Statement

A solid metal ball of radius 1.5 cm bearing a charge of -16 nC is located near a hollow plastic ball of radius 2 cm bearing a uniformly distributed charge of -4 nC on its outer surface. The distance between the centers of the balls is 8 cm.

What is the electric field at the center of the metal ball due only to the charges on the surface of the metal ball?

Homework Equations

The Attempt at a Solution

am I missing something, because I though that the electric field due to surface charges inside a conductor is zero, therefore shouldn't the answer to this question be the zero vector. I must be missing some concept because the question before this one asks about the net E field and I know that is zero, so how would I figure out the electric field due only to the surface charges. Should I treat the surface as a hollow sphere, that doesn't seem right either.

 

[gneill]

Have a look http://en.wikipedia.org/wiki/Electrostatics" [Broken]at the diagram showing conductive surfaces in an electrostatic field.

 

[DJsTeLF]

Should I treat the surface as a hollow sphere, that doesn't seem right either.

No, as you suspect. If the question says metal ball I think in means a solid sphere of metal; conductor.