1. Two point charges, *q *each, are attached to the ends of a rigid rod of length . The rod is rotated with an angular speed about an axis through the centre of the rod and perpendicular to it. Calculate the electric and the magnetic dipole moment of the system taking the centre of the rod as the origin. What is the total power radiated by this system?

The electric dipole moment about the centre is zero as the position vector of the two (equal) charges are always directed oppositely. Magnetic dipole moment can be calculated by observing that charge 2q is rotating with a time period

, which is equivalent to a current

. The area of the current loop is

. Thus the magnetic moment is given by

. Both the electric and the magnetic dipoles are constant in time and hence there is no radiation emitted by the system.