Question

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 :

• A. M
• B. $\frac{M}{2}$
• C. 2M
• D. $\frac{M}{\sqrt3}$

Answer 1

Answer: (B)

$\frac{M}{2}$

Answer 2

When the bar is bent at an angle $\theta = 60^\circ$, the effective magnetic moment is:
$M_{new} = M \cos{\frac{\theta}{2}}$.
Substitute $\theta = 60^\circ$:
$M_{new} = M \cos{30^\circ} = M \cdot \frac{\sqrt{3}}{2}$.
The effective length is halved, so:
$M_{final} = \frac{M}{2}$