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JEE Main & Advanced Sample Paper JEE Main Sample Paper-27

  • question_answer
    A bar magnet when placed at an angle of \[30{}^\circ \] to direction of magnetic field induction of \[5\times {{10}^{-2}}T,\]experience of moment of couple  \[25\times {{10}^{-6}}Nm.\] Nm. If the length of the magnet is 5 cm, then its pole strength is:

    A)  \[2\times {{10}^{-2}}Am\]     

    B)  \[5\times {{10}^{-2}}Am\]

    C)  \[2\,Am\]                                 

    D)  \[5\,Am\]

    Correct Answer: A

    Solution :

    We know that, torque \[\tau \,=MB\sin \theta \] \[\Rightarrow \,\,\tau \,=(ml)\,B\sin \theta \] \[\Rightarrow \,\,25\,\times {{10}^{-6}}\,=(m\times 5\times {{10}^{-2}})\,\times 5\times {{10}^{-2}}\,\times \sin {{30}^{0}}\] \[\Rightarrow \,\,m=2\times {{10}^{-2}}\,Am\]


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