Consider the plane of the paper to be vertical plane with direction of ′g′ as shown in the figure. A rod (MM′) of mass ′M′ and carrying a current I. The rod is suspended vertically through two insulated spring of spring constant K at two ends. A uniform magnetic field is applied perpendicular to the plane of the paper such that the potential energy stored in the spring, in equilibrium position is zero. If the rod is slightly displaced in the vertically direction from the position of equilibrium, then the time period of oscillation is