A thick spherical shell (inner radius a, outer radius b) is made of dielectric material with a "frozen-in" polarization P(ār) = (k/r)rĢ, where k is a constant and r is the distance from the center (Fig. 4.18). (There is no free charge in the problem.) Find the electric field in all three regions by two different methods:
(a) Locate all the bound charge, and use Gauss's law to calculate the field it produces.
(b) Use ā§āDā ā dÄ = Q_{f,enc} to find D, and then get E from Dā = εāEā + Pā. [Notice that the second method is much faster, and it avoids any explicit reference to the bound charges.]