The Potential outside a Charged Disk The z-axis is the symmetry axis of a disk of radius R which lies in the x- y plane and carries a uniform charge per unit area a. Let Q be the total charge on the disk. (a) Evaluate the exterior multipole moments and show that (9)QiR2P(O)P( 9) R (pr, _471'0r70 r +2 ECOS r> I (b) Compute the potential at any point on the z-axis by elementary means and conrm that your answer agrees with part (a) when 2 > R. Note: Pg(1) = 1