We have a straight magnetised wire with magnetic moment M. If we bend the wire to give it a shape as shown in the figure, with all parts equal in length, then what will be the new magnetic moment of the wire?

Explanation

We can see in the figure that the distance between poles has become AB,
`AB = sqrt( (L/5)^2 + ( (2L)/(5))^2) = (L)/(sqrt5)`
M = mL
`M_("net") = m ((L)/(sqrt5)) = (M)/(sqrt5)`