What is the charge density on the insulator?

[Luke0034]

Homework Statement

Insulator has a 3 cm radius and is a sphere. It has a total charge of -4.2 uC. I need to find the charge density of the insulator.

Homework Equations

sigma = total charge / volume... I think?

The Attempt at a Solution

After using the above equation, I got -3.714E-8 C/m

I am just not sure if this is the correct charge density for the insulator. I know that for conductors, I think the equation would be charge/area, but I think since an insulator contains the charge throughout the sphere and not just on the surface, you'd have to use volume correct? I am correct in my answer and thinking?

 

[BvU]

Thinking is good, but I can't see your calculation (telepathic powers lacking) and the dimension of the answer seems a bit strange to me. Value also.