Time period of oscillations with a standard rectangular bar magnet the time period of a vibration magnetometer is 4 seconds. The bar magnet is cut parallel to its length into four equal pieces. The time period is, when one piece is used (in seconds) …………

T=2πIMBH=4sec...........(1)When bar magnet is cut in 4 parts along length,  its pole strength and mass becomes (14)th but length remains same.Moment of Inertia = mass×length212 ∴I' = I4Magnetic Moment = pole strength ×length ∴M' = M4New Time Period will be, T1=2πI4M4BH=2πIMBH = 4 sec   [from equation (1)]