2.(30%) For two concentric spherical shells with radius a and b, respectively (a < b), there is a linear dielectric material between them with dielectric constant . If the inner shell (r= a) carries uniform charge Q (2a) Compute the electric field E. (2b) Compute the polarization P. (2c) Show that the inner shell (r= a) has charge Q' = (co/e)Q, the so-called shielding effect.