Magnetic moment of a thin bar magnet is 'M.' If it is bent into a semicircular form, its new magnetic moment will be _________.

Fill in the blank with the correct answer from the options given below.

$2 M / \pi$

Initial magnetic moment is $ M = mL$

Final magnetic moment is $ M' = m\times 2R $

$ L = \pi R \Rightarrow M' = m\times \frac{2L}{\pi} = \frac{2M}{\pi}$

The correct answer is Option (4) → $2 M / \pi$