A point charge 2q is placed at the center of a ring charge -q of radius a.
(a) Determine q for R > a up to but not including terms in R4 using the expansion formula for 93.
(b) Show by direct calculation that this is correct for any point on the symmetry axis.
(c) Find and sketch a symmetrical arrangement of point charges (multiples) that would produce the same potential as the actual charge distribution does up to the terms in R4.