A bar magnet of magnetic moment M is bent into a semicircular form. Its new magnetic moment will be:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 2M/\pi \)
The magnetic moment is the pole strength times the straight-line distance between the poles, \( M = m \times L \). Bending the magnet does not change the pole strength, but it brings the poles closer.
The length \( L \) now forms a semicircle of radius \( r \), and the poles sit at the two ends of its diameter.
\( \displaystyle L = \pi r \;\Rightarrow\; r = \frac{L}{\pi} \)
\( \displaystyle M' = m \times 2r = m \times \frac{2L}{\pi} = \frac{2M}{\pi} \)
Note: A similar question was also asked in CUET (UG) 2024 on 16-05-2024 (Slot 1).