Find the energy stored in a uniformly charged solid sphere of radius R and charge q. Do it three different ways:
(a) Use Eq. 2.43. You found the potential in Prob. 2.21.
(b) Use Eq. 2.45. Don't forget to integrate over all space.
(c) Use Eq. 2.44. Take a spherical volume of radius a. What happens as a→∞?