Question

An iron rod of length L and magnetic moment M is bent in the form of a semicircle. Now its magnetic moment will be

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

Answer 1

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

On bending a rod it’s pole strength remains unchanged where as its magnetic moment changes.
New magnetic moment $M^{\prime }=m\left(2R\right)=m\left(\frac{2L}{\pi }\right)=\frac{2M}{\pi }$