Question

A bar magnet for dipole moment $M$ is bent to forms a semi-circle. Find new dipole moment :

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

Answer 1

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

Bar magnet is bent to form a semi-circle
$\pi r=l$ or
Radius of circle $r=\frac{l}{\pi }$
new dipole moment $M^{{}^{\prime }}=m\left(2r\right)=\frac{m\left(2l\right)}{\pi }=\frac{2M}{\pi }$