Two positive charges Q and 4Q are placed at points A and B respectively, where B is at a distance d units to the right of A. The total electric potential due to these charges is minimum at P on the line through A and B. What is (are) the distance (s) of P from A?

A charged particle of mass m₁ and charge q₁ is revolving in a circle of radius r. Another charged particle of charge q₂ and mass m₂ is situated at the centre of the circle. If the velocity and time period of the revolving particle be v and T respectively, then