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. Notice what happens as a → ∞.