Q 12-05-003NEETNEET 2024Top questionMedium
An iron bar of length L has magnetic moment M. It is bent at the middle of its length such that the two arms make an angle $60°$ with each other. The magnetic moment of this new magnet is:
Answer: (D) $\dfrac{M}{2}$
Concept. Bending a magnet keeps the pole strength $m$; only the straight-line distance between the poles changes, and $M = m \times$ (pole separation).
Step 1. Original magnet. $M = mL$.
Step 2. Geometry after bending. Each arm is $\dfrac{L}{2}$ long and the arms meet at $60°$. The two arms and the line joining the ends form an equilateral triangle, so the poles are now $\dfrac{L}{2}$ apart.
Step 3. New moment.
$$M' = m \cdot \frac{L}{2} = \frac{M}{2}$$
Answer. $\dfrac{M}{2}$ (Option D).
Solution by Sreeraj P, M.Sc Physics