Question

The magnetised wire of moment $M$ and length $l$ is bent in the form of semicircle of radius $r$. Then its magnetic moment is

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

Answer 1

The correct option is C $\frac{M}{\pi }$

We have length= l, moment=M

Therefore magnetic moment; $m=Ml$

Now l changes to semicircle

therefore $l=\pi r$

$⟹r=\frac{l}{\pi }$

Now new magnetic moment

$=M\times r=\frac{Ml}{\pi }=\frac{M}{\pi }$