Q. A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc of a circle of radius r subtending an angle of 60° at the centre. The new magnetic dipole moment will be
A) M
B) (3/π)M
C) (2/π)M
D) M/2
Explanation
[Solution from source] Pole strength stays m with M = ml. The arc length l = r(π/3), so r = 3l/π. The poles are now joined by a chord subtending 60°, whose length equals r, so M′ = m × 3l/π = 3M/π. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.