Question

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 and angle θ with the magnetic meridian such that

• A. $\theta = \tan ^ { - 1 } \left( \frac { 1 } { \sqrt { 3 } } \right)$
• B. $\theta = \tan ^ { - 1 } ( \sqrt { 3 } )$
• C. $\theta = \tan ^ { - 1 } \left( \frac { 1 } { 2 } \right)$
• D. $\theta = \tan ^ { - 1 } \left( \frac { 3 } { 4 } \right)$

Answer 1

Answer: (C)

$\theta = \tan ^ { - 1 } \left( \frac { 1 } { 2 } \right)$

Answer 2

$\Rightarrow \tan \theta = \frac { M } { 2 M } = \frac { 1 } { 2 } \Rightarrow \theta = \tan ^ { - 1 } = \frac { 1 } { 2 }$