Question

A charge Q is uniformly distributed only on the fourths portion of a ring of radius R. The elctric potential at centre of ring is

Answer 1

Let us consider a semi-circular ring with uniform charge q with radius r.

Let λ be the charge density of the ring.

Now the electric field dE due to a small length dl at centre O is resolved into two components dEx and dEy.

We see the electric field is directed away from the centre