Q. A steel wire of length $l$ has a magnetic moment $M.$ It is bent at its middle point at an angle of 60${^\circ}$. Then the magnetic moment of new shape of wire will be
A) $M/\sqrt{2}$
B) $M/2$
C) $M$
D) $\sqrt{2}M$
Explanation
(b) Pole strength $= m = \frac{M}{l}$. When the wire is bent at its middle point $O\ at\ 60{^\circ},$ then as is clear from figure.
[image:5_image43.emf]
$60{^\circ} + \theta + \theta = 180{^\circ}$
$2\theta = 180{^\circ} - 60{^\circ} = 120{^\circ},$
$\therefore OAB$ is an equilateral triangle.
$\therefore AB = 2l^{''} = l/2$
New magnetic moment
$M^{''} = m\left( 2l^{''} \right) = \frac{ml}{2} = \frac{M}{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.