# A plastic rod has been formed into a circle of radius R. It has a positive charge $+Q$ uniformly distributed along one-quarter of its circumference and a negative charge of $–6Q$ uniformly distributed along the rest of the circumference as shown in figure. With V = 0 at infinity.

(D) the electric potential at point P, which is on the central axis of the circle at distance z from the center is $-\large\frac{5Q}{4 \pi \in_0 \sqrt {r^2+z^2}}$