Question

A magnetised wire of magnetic moment $M$ and length $L$ is bent in the form of a semicircle of radius $r$. Then its magnetic moment is:

• A. $\frac{2M}{\pi }$
• B. $2M$
• C. $\frac{M}{\pi }$
• D. $0$

Answer 1

The correct option is A $\frac{2M}{\pi }$

On bending a wire it pole strenth is not affected but its moment changes.
Magnetic moment of straight wire $M=ml$
Radius of bent wire $r=\frac{l}{\pi }$

Magnetic moment of bent wire
$M_{New}=m\left(2r\right)=m\frac{2l}{\pi }=\frac{2M}{\pi }$