A light brass wire of total resistance R=1ohm is wound around a disc of plastic (den =1 gm/cc) &suspended so as 2 make an essentially undamped torsion pendulum of period T = 10 sec.......The disc is initially at rest in a uniform magnetic field , B=10,000Gauss , with B in d plane of d loop,i.e. theta = 90.......At time t=0,switch S is switched to M and then at t1=10^(-4)sec switched to N....Find d amplitude of d ensuing oscillations as a function of t..............

A torsional pendulum, or torsional oscillator, consists of a disk-like mass suspended from a thin rod or wire. When the mass is twisted about the axis of the wire, the wire exerts a torque on the mass, tending to rotate it back to its original position. If twisted and released, the mass will oscillate back and forth, executing simple harmonic motion. This is the angular version of the bouncing mass hanging from a spring. This gives us an idea of moment of inertia. We try to calculate the moment of intertia of a ring given the moment of a disc. We can also verify the perpendicular axis theorem and compare it with theoretically calculated values. The working is based on the torsional simple harmonic oscillation with the analogue of displacement replaced by Angular displacement θ, Force by Torque τ and the dpring constant by torsinal constant κ.