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BCECE Medical BCECE Medical Solved Papers-2012

  • question_answer
    A bar magnet has 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 that should be sent through the solenoid is

    A)  8 A            

    B)  10A

    C)  12 A          

    D)  14 A

    Correct Answer: A

    Solution :

    The coercivity of bar magnet is \[4\times {{10}^{3}}A{{m}^{-1}}\] i.e., it requires a magnetic intensity\[H=4\times {{10}^{3}}A{{m}^{-1}}\] to get demagentised. Let \[i\] be the current carried by solenoid having n number of turns per metre length, then                 \[H=ni\] Here      \[H=4\times {{10}^{3}}A{{m}^{-1}}\] and        \[n=\frac{N}{l}=\frac{60}{0.12}=500\] turn/m \[\therefore \] \[i=\frac{H}{n}=\frac{4\times {{10}^{3}}}{500}=8.0\,\,A\]


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