JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    A circular coil carrying a current has a radius\[R\]. The ratio of magnetic induction at the centre of the coil and at a distance equal to \[\sqrt{3}R\] from the centre of the coil on the axis is:

    A) \[1:1\]  

    B) \[1:2\]

    C) \[2:1\]                                  

    D) \[8:1\]

    Correct Answer: D

    Solution :

    The magnetic field \[(B)\] at a distance \[x\] from the circular coil is given by                 \[B=\frac{{{\mu }_{0}}ni{{R}^{2}}}{2{{({{R}^{2}}+{{x}^{2}})}^{3/2}}}\] where \[R\] is radius of the coil. At centre,\[x=0;\,\,\,\,\,\,\,\,{{B}_{0}}=\frac{{{\mu }_{0}}ni}{2R}\] At\[x=\sqrt{3}R\] \[\therefore \]\[{{B}_{a}}=\frac{{{\mu }_{0}}ni{{R}^{2}}}{2{{({{R}^{2}}+3{{R}^{2}})}^{3/2}}}=\frac{{{\mu }_{0}}ni}{16R}\] Hence,                  \[\frac{{{B}_{0}}}{{{B}_{a}}}=\frac{8}{1}\]


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