# Homework Help: Electrostatics - conductors.

1. Feb 9, 2008

### cosmic_tears

I'll try my best to describe the question, though Enligsh is not my mother-tounge. Hope I'm clear enough!

the problem:
There's a thick spherical shell made of insulated material (like a thick ring), with an inner radius a and outer radius b. The shell is charged with a changing charge density (volumic... if that's how you say it) : P = c/r (r = distance from center, c= given const.)

The shell is coated from the inside *and* from the outside with thin conducting material layers (2-dimentional).

The charge of the outer thin conducting layer is 2*pi*c*a^2
The charge of the inner thin conducting layer is -2*pi*c*b^2

They ask what's the electrostatic energy of the system.

2. Relevant equations

I don't know how to insert equations here, I'm sorry, but anyhow it's not important because I have a theoratical question.

3. The attempt at a solution

There's an equation tying the enrgy to a 3D intergral on all of "space", of the squared electrostatic field the system creates.
However, I'm having trouble understanding what's the significence of the conducting layers. What's their effect on the problem? What's the difference between them being conducting or not? How would the problem be different if they were not conducting?

If I would attempt to solve it, I would just calculate the field using Gaus' law in the area of the inner vacum created by the spherical shell (r<a) (0), in the thick shell itself (a<r<b) and on the outside (b<r), and then use the equation. But I have to assume to fact that the layers are conducting has some meaning...

Any hints? Tips? Greatly appreciated!
I hope I wasn't too vauge!