Two bar magnets are tied together side by side and suspended so as to oscillate about their centre of gravity in a horizontal plane. Compare their magnetic moments, when one magnet is reversed the period of oscillations are 12 second and 4 second

A bar magnet is vibrating in uniform magnetic field of induction B about transverse axis passing though its centre. When the value of B is reduced by 3xx10^-5 Wb/m^2 , the period of the vibrating magnet gets doubled. What is the original value of B ?