In previous publications, we illustrated the effectiveness of the method of the inhomogeneous
differential equation in calculating the electric polarizability in the one-dimensional problem. In
this paper, we extend our effort to apply the method to the three-dimensional problem. We calculate
the energy shift of a quantum level using second-order perturbation theory. The energy shift is then
used to calculate the electric polarizability due to the interaction between a static electric field
and a charged particle moving under the influence of a spherical delta potential. No explicit use of
the continuum states is necessary to derive our results.