A steel wire of length $‘ l ’$and magnetic moment ‘M’ is bent into a semicircular arc, Then new magnetic moment is

$l=\pi r\text{, where }r\text{ is the radius of the semicircle }$

$\therefore r=l/\pi$

Magnetic moment of straight wire, $M=ml$

Magnetic moment of semicircular wire, $M\text{'}=m\left(2r\right)=m2\frac{l}{\pi }=\frac{2}{\pi }M$