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BCECE Engineering BCECE Engineering Solved Paper-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)  10 A                     

    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 demagnetized. 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 \[n=\frac{N}{l}=\frac{60}{0.12}=500\,\text{turn/m}\] \[\therefore \]  \[i=\frac{H}{n}=\frac{4\times {{10}^{3}}}{500}=8.0\,A\]


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