Static charge density vs free charge density

[superg33k]

Homework Statement

A solid metal sphere of radius 'a' is concentric with a hollow metal sphere of inner radius '2a'. The space between the spheres is filled with a dielectric material of relative permittivity 'ε' carrying a uniform static charge density 'ρ0'. The charge density is zero outside the spheres.

My question:

In the answers at the back of my book 'p0' is equated to the free charge density 'pf'. Shouldn't it be equated to charge density?

I know I'm getting hung up on the wording but it might show a large gap in my understanding of dielectrics.

Homework Equations

Charge density = free charge density + bound charge density

The Attempt at a Solution

 

[tiny-tim]

hi superg33k!

as you know, an insulator can have a surface charge, and that will be free charge exactly the same as the free surface charge of a conductor …

unlike a conductor (in equilibrium), an insulator can also have free charge in the interior in the same way as it has on the surface (nothing to do with polarisation)

and "dielectric" is just a fancy word for "insulator"!

(the dielectric may of course also have some bound charge, due to polarisation, in the interior)