(a) Using Eq. 24-32, show that the electric potential at a point on the central axis of a thin ring (of charge q and radius R) and at distance e from the ring is V = 1/4πε0 q/√z2 + R2 

(b) From this result, derive an expression for E at points on the ring's axis; compare your result with the calculation of or in Section 22-6.