charging a spherical shell

[grief]

the problem is: "Calculate the work that must be done to charge a spherical shell of radius R and total charge Q", and I have no idea where to start. You probably have to write some sort of an integral but I don't know how. Can anyone give me a hint?

[grief]

the answer, by the way is ke*Q^2/(2R), if that helps

[Astronuc]

Think about the equivalence of work and energy, and the fact that charging a sphere changes the electric potential energy.

[grief]

I know that work is equal to the change of potential energy, but the potential energy of what? Won't it be just keQ/r^2. How does the fact that it is a spherical shell affect the problem?