2-15. A spherical charge distribution has a volume charge density which is a function only of r, the distance from the center of the distribution. In other p(r). If p(r) is as given below, determine the electric field as a words, p = function of r. Integrate the result to obtain an expression for the electro- static potential U(r), subject to the restriction that l() = 0. A/r with A a constant for 0r2 R; (a) p = p = 0 for r > R. (b) p po (i.e., constant) for 0 2 r > R; p = 0 for r> R.