State the Biot-Savart law which gives the magnetic field B at a distance r from a current element. Hence obtain an expression for the magnetic field BQ due to a point charge Q moving with constant velocity v (assumed non-relativistic). Point charges Q and Q’ are constrained to move along the x-and y-axes, respectively, with the same uniform speed v. At time r = 0 both charges are at the origin. At time t calculate the Lorentz force F on Q’ due to the magnetic field of Q.