A thin magnetic iron rod of length 30 cm is suspended in a uniform magnetic field. Its time period of oscillation is T second. It is broken into three equal parts perpendicular to axis. The time period of oscillation of one part when suspended in the same magnetic field is

T=2πIMBWhere given rod is broken into three equal parts then mass and length becomes one third but pole strength remains same.We know that, Magnetic Moment = Pole Strength ×length ; Moment of Inertia  = Mass ×Length212Hence,  M1=M9 and I1=I27 (MI of each piece)T1=2πI1M1B T1=2π9I27MB=2πIMB13=T3