A plastic rod has been bent into a circle of radius R = 5.10 cm. It has a charge Q1 = +3.60 pC uniformly distributed along one-quarter of its circumference and a charge Q2 = -6Q1 uniformly distributed along the rest of the circumference.
(a) What is the electric potential at the center C of the circle?
(b) What is the electric potential at point P, which is on the central axis of the circle at distance D = 6.71 cm from the center?