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  3. BCECE Medical

BCECE Medical BCECE Medical Solved Papers-2006

  • question_answer
    A bar magnet has a coercivity \[4\times {{10}^{3}}A{{m}^{-1}}\]. It is desired to demagnetise it by inserting it inside a solenoid 12 cm long and having-60 turns. The current carried by the solenoid should be :

    A)  8 A              

    B)  6 A

    C)  4.5 A             

    D)  2 A

    Correct Answer: A

    Solution :

    From relation \[B=\mu {{\,}_{0}}H\] or            \[\mu {{\,}_{0}}ni=\mu {{\,}_{0}}H\] or            \[\frac{Ni}{L}=H\] \[\left( \because \,\,n=\frac{N}{L} \right)\] or            \[i=\frac{HL}{N}\] Given,   \[H=4\times {{10}^{3}}A{{m}^{-1}}\]                 \[L=12\,cm=12\times {{10}^{-2}}m\]                 \[N=60\]turns \[\therefore \] \[i=\frac{4\times {{10}^{3}}\times 12\times {{10}^{-2}}}{60}=8\,A\]


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