The work done in carrying a charge q once round a circle of radius r with a charge Q at the centre is

The work done in carrying a charge 'a' once round a circle of radius 'a' with a charge Q at its centre is

The work done in carrying a charge Q_(1) once round a circle of radius R with a charge Q_(2) at the centre is

Work done to carry a charge q once along the circular path of radius r with charge q' at its centre, will be

A unit positive charge is moved along the circumfer-ence of a circle of radius, r with a -5muC charge at the centre at the centre of the circle. Then, the work done in the process is "______" .