Bar Magnet & Magnetic Moment question from NEET 2024

Answer: (a)

1. Pole strength $m = M/L$ is unchanged; $M' = m\times$ chord.
2. Arc $L$ subtends $60^\circ = \pi/3$: $r = \dfrac{3L}{\pi}$.
3. With $60^\circ$ at the centre the triangle is equilateral, so chord $= r = \dfrac{3L}{\pi}$.
4. $M' = \dfrac{M}{L}\cdot\dfrac{3L}{\pi} = \dfrac{3M}{\pi}$
5. So the answer is (a) $\frac{3M}{\pi}$.