A thin uniform rod with negligible mass and length `l` is attached to the floor by a frictionless hinge at point `P`. A horizontal spring with force constant `k` connects the other end to wall. The rod is in a uniform magnetic field `B` directed into the plane of paper. What is extension in spring in equilibrium when a current is passed through the rod in direction shown? Assuming spring to be in natural length initially and it remains perpendicular to wall always.