JEE Main & Advanced Physics Magnetism Question Bank Critical Thinking

  • question_answer
    Two magnets of equal mass are joined at right angles to each other as shown the magnet 1 has a magnetic moment 3 times that of magnet 2. This arrangement is pivoted so that it is free to rotate in the horizontal plane. In equilibrium what angle will the magnet 1 subtend with the magnetic meridian

    A)            \[{{\tan }^{-1}}\left( \frac{1}{2} \right)\]

    B)            \[{{\tan }^{-1}}\left( \frac{1}{3} \right)\]

    C)            \[{{\tan }^{-1}}(1)\]

    D)             0°

    Correct Answer: B

    Solution :

               For equilibrium of the system torques on M1 and M2 due to BH must counter balance each other i.e. \[{{M}_{1}}\times {{B}_{H}}={{M}_{2}}\times {{B}_{H}}\]. If q is the angle between M1 and BH will be \[(90-\theta )\]; so \[{{M}_{1}}{{B}_{H}}\sin \theta ={{M}_{2}}{{B}_{H}}\sin (90-\theta )\]            \[\Rightarrow \tan \theta =\frac{{{M}_{2}}}{{{M}_{1}}}=\frac{M}{3M}=\frac{1}{3}\Rightarrow \theta ={{\tan }^{-1}}\left( \frac{1}{3} \right)\]


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