Bar Magnet & Magnetic Moment question from MHT CET 2023 (9 May, Shift 2)

Answer: (d)

1. Pole strength $m = M/L$ stays the same; the new moment is $m \times$ (straight distance between the ends).
2. Semicircle of length $L$: $\pi r = L \Rightarrow r = L/\pi$.
3. Distance between ends $= 2r = 2L/\pi$.
4. $M' = \dfrac{M}{L}\cdot\dfrac{2L}{\pi} = \dfrac{2M}{\pi}$
5. So the answer is (d) $\frac{2M}{\pi}$.