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BCECE Engineering BCECE Engineering Solved Paper-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,   \[H=4\times {{10}^{3}}A{{m}^{-1}}\]                 \[L=12\,cm=12\times {{10}^{-2}}m\] \[N=60\,\text{turns}\] \[\therefore \]  \[i=\frac{4\times {{10}^{3}}\times 12\times {{10}^{-2}}}{60}=8A\]


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