JCECE Engineering JCECE Engineering Solved Paper-2014

  • question_answer
    A charge \[q\] coulomb makes \[n\] revolutions in one second in a circular orbit of radius r. The magnetic field at the centre of the orbit in\[N{{A}^{-1}}{{m}^{-1}}\]is.

    A) \[\frac{2\pi rn}{q}\times {{10}^{-7}}\]

    B) \[\left( \frac{2\pi q}{r} \right)\times {{10}^{-7}}\]

    C) \[\left( \frac{2\pi q}{nr} \right)\times {{10}^{-7}}\]

    D) \[\left( \frac{2\pi nq}{r} \right)\times {{10}^{-7}}\]

    Correct Answer: D

    Solution :

    Magnetic field at the centre                 \[B=\frac{{{\mu }_{0}}nl}{2r}\]                 \[B=\frac{2{{\mu }_{0}}nl}{4r\pi }\times \pi \]                 \[B=\frac{2{{\mu }_{0}}nl\pi }{4\pi r}\]                 \[B=\frac{2\pi nl}{r}\times {{10}^{-7}}\]       \[\left[ \because \frac{{{\mu }_{0}}}{4\pi }={{10}^{-7}} \right]\]                 \[B=\left( \frac{2\pi nq}{r} \right)\times {{10}^{-7}}\]  \[[\because \,\,q=lt]\]


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