The time period T of oscillation of a magnet is given by T=2π√
I
MB
where, I= Moment of inertia of magnet about the axis of rotation M= Magnetic moment of the magnet B= Uniform magnetic field As the I, B remains the same ∴T∝
1
√B
or
T2
T1
=√
B1
B2
According to given problem, B1=24µT B2=24µT−18µT=6µT T1=2s ∴T2=(2s)√