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JEE Main & Advanced Physics Magnetism Question Bank Self Evaluation Test - Magnetism and Matter

  • question_answer
    A bar magnet having a magnetic moment of \[2\times {{10}^{4}}J{{T}^{-1}}\] is free to rotate in a horizontal plane. A horizontal magnetic field \[B=6\times {{10}^{-4}}T\] exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction \[60{}^\circ \] from the field is

    A) 12 J     

    B) 6 J

    C) 2 J       

    D) 0.6 J

    Correct Answer: B

    Solution :

    [b] Work done\[=MB(\cos \,{{\theta }_{1}}-\cos \,{{\theta }_{2}})\] \[=MB(\cos \,{{0}^{o}}-\cos \,{{60}^{o}})\] \[=MB\left( 1-\frac{1}{2} \right)=\frac{2\times {{10}^{4}}\times 6\times {{10}^{-4}}}{2}=6\,J\]


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