# Potential energy - Purcell

1. Jun 18, 2006

### ffdbzathf

A spherical volume of radius, a, is filled with charge of uniform density, p. We want to know the potential energy, U, of this sphere of charge, that is, the work done in assembling it. Calculate it by building the sphere up layer by layer, making use of the fact that the field outside a spherical distribution of charge is the same as if all the charge were at the center. Express the result in terms of the total charge, Q, in the sphere.

2. Jun 18, 2006

### arildno

That was a nice rendition of your exercise question!

Now, going over to the really big issue:
Have you done anything at all?

3. Jun 18, 2006

### ffdbzathf

Exercise question? This is not for school dude...it's june, school is over. I'm working out of a book called Electricity and Magnetism by Purcell, by myself, and have gotten stuck on this question. Thank you so much for being helpful.

4. Jun 19, 2006

### siddharth

The forum rules require you to show your work (or thoughts/ideas) before you get help.

Also, if you drop the sarcasm, people might be more tempted to help