Using a bar magnet `P`, a vibration magnetometer has time period 2 sec. When a bar Q (identical to P in mass and size) is placed on top of P, the time period is unchanged. Which of the following statements is true?

Options

A. `Q` is of non-magnetic material
B. `Q` is a bar magnet identical to `P`, and its north pole placed on top of `P`'s north pole
C. `Q` is of unmagnetized ferromagnetic material
D. Nothing can be said about `Q`'s properties

Answer

B

Explanation

`T=2pisqrt(I/(MB_(H)))`. If `Q` is an identical bar magnet then time period of system will be `T^(')=2pisqrt((2I)/((2M)B_(H)))=T`