Two bar magnets of the same length and breadth but having magnetic moments `M` and `2M` are joined with like poles together and suspended by a string. The time of oscillation of this assembly in a magnetic field of strength `B` is `3` sec. What will be the period of oscillation, if the polarity of one of the magnets is changed and the combination is agnain made to oscillate in the same field ?

Explanation

As magnetic moment is a vector, so when magnets are joined with like poles together `M_(1)=M+2M=3M,` so
`T=2pisqrt(((I_(1)+I_(2)))/(3MB)) …….(1)`
When the polarity of one of the magnets is reversed, `M_(2)=M~2M=M,`
so `T'=2pisqrt(((I_(1)+I_(2)))/(MB)) ..........(2)`
Dividing `Eq.(2)"by"(1)`,
`(T')/(T)=sqrt3, i.e.,T'=(sqrt3)T=3sqrt3 sec`