Extra Problem A4 for 7D [just one this week]. Please upload your solution to the course website by 11:59 Tuesday 5/2/2023 A device consists of a spherical solid insulator with uniform charge density of radius a, and an outer concentric metal spherical shell of radius b. Assume the metal is thin compared to other dimensions (a,b) so no need to worry about the thickness of the shell. The total charge on the inner sphere is +Q and the total charge on the outer shell is -Q. Assume the potential is zero at radius b. So V(b)=0. a) Compute the Electric field for rb is 0 by Gauss's law. Write the expression for E at distances r