A bar magnet of lenth `l` and magnetic dipole moment 'M' is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be

Options

A. `M/2`
B. `M`
C. `3/piM`
D. `2/piM`

Explanation

Before bending, strength of each pole,
`m=M/l`
On bending, as shown in figure, distance between poles `=AB=2rsin. (60^@)/(2)=r`
`:.` New magnetic moment, `M^'=mxxr`
`M^'=M/lxx(l)/(pi//3)=(3M)/(pi)`
choice (c) is correct.