Bar Magnet & Magnetic Moment question from MHT CET 2020 (19 Oct, Shift 2)

Answer: (c)

1. Pole strength $m = M/\ell$ is unchanged on bending.
2. Semicircle: $\pi r = \ell \Rightarrow r = \ell/\pi$; end-to-end distance $= 2r = 2\ell/\pi$.
3. $M' = \dfrac{M}{\ell}\cdot\dfrac{2\ell}{\pi} = \dfrac{2M}{\pi}$
4. So the answer is (c) $\frac{2M}{\pi}$.