Rho (greek letter, not sure on spelling)

[Bad-Wolf]

I don't quite understand how to use rho charge per volume. I understand the applications of lamda and sigma as sigma is useful Gauss's Law and lambda is easy when dealing with wires and such. However, how the hell do you use charge per volume? I mean charges only occupy the surfaces of conductors... What law or physical concept can I use to determine how a sphere with volume charge density rho would effect well anything.

Basically, what laws or tricks do I use when working with rho? How could a sphere have a volume charge density when all the charges are on the surface to begin with?

 

[UTDphysmace]

I believe charge per unit volume applies when you are dealing with an insulating object that has had a charge applied to it. As my prof would say, when you apply a charge to an insulating object, the charge stays where you put it. so if you have an insulating object with the charge evenly distributed throughout, it stays there, rather than moving to the surfaces, thus charge is equally distributed through the volume of the object.

please anyone correct me if I'm wrong.