Q. Two bar magnets with magnetic moments $2\ M$ and $M$ are fastened together at right angles to each other at their centres to form a crossed system, which can rotate freely about a vertical axis through the centre. The crossed system sets in earth’s magnetic field with magnet having magnetic moment $2M$ making an angle $\theta$ with the magnetic meridian such that
A) $\theta = \tan^{- 1}\left( \frac{1}{\sqrt{3}} \right)$
B) $\theta = \tan^{- 1}\left( \sqrt{3} \right)$
C) $\theta = \tan^{- 1}\left( \frac{1}{2} \right)$
D) $\theta = \tan^{- 1}\left( \frac{3}{4} \right)$
Explanation
(c) $\Rightarrow \tan\theta = \frac{M}{2M} = \frac{1}{2} \Rightarrow \theta = \tan^{- 1}\left( \frac{1}{2} \right)$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.