5. The lower end of the thin uniform rod in the Figure is attached to the floor by a frictionless hinge at point P. The rod has mass m and length L and is immersed in a uniform magnetic field B that is directed into the page. The rod finds an equilibrium position due to the force exerted by a horizontal spring that connects the top of the rod to the wall. The spring extension was zero before the current I was switched on and then extended to a distance of d after the current was on. The rod carries the current I in the direction toward P. The equilibrium angle after the current is switched on is q. Find the spring constant k. (hint: Find the torques due to the magnetic force, weight and the force due to the spring. Take the axis point to be P. You can take the weight acting at the center of the rod. Think about how you are going to calculate the torque due to the magnetic force. Can you use an integration? If not, use an approximation).