JEE Main & Advanced Physics Magnetism Question Bank Magnet and its Properties

  • question_answer
    The work done in turning a magnet of magnetic moment 'M' by an angle of 90° from the meridian is 'n' times the corresponding work done to turn it through an angle of 60°, where 'n' is given by              [CBSE PMT 1995; MP PET 2003]

    A)            1/2

    B)            2

    C)            1/4

    D)            1

    Correct Answer: B

    Solution :

                       \[{{W}_{1}}=MB(\cos {{0}^{o}}-\cos {{90}^{o}})=MB(1-0)=MB\]                    \[{{W}_{2}}=MB(\cos {{0}^{o}}-\cos {{60}^{o}})=MB\left( 1-\frac{1}{2} \right)=\frac{MB}{2}\]            \[\therefore \ {{W}_{1}}=2{{W}_{2}}\Rightarrow n=2\]


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