The time period T of oscillation of a magnet is given by T=2π√
I
MB
Where, I = Moment of inertia of the 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)√