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NEET NEET SOLVED PAPER 2016 Phase-I

  • question_answer
    A long straight wire of radius a carries a steady current \[\text{I}\text{.}\]The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distances \[\frac{a}{2}\]and 2a respectively, from the axis of the wire is :                                                                                                                                                          

    A)  \[\frac{1}{4}\]                                  

    B)  \[\frac{1}{2}\]

    C)   1                                           

    D)  4            

    Correct Answer: C

    Solution :

                     For points inside the wire \[B=\frac{{{\mu }_{0}}Ir}{2\pi {{R}^{2}}}(r\le R)\] For points outside the wire \[B=\frac{{{\mu }_{0}}I}{2\pi R}(r\ge R)\] according to the question \[\frac{B}{B'}=\frac{\frac{{{\mu }_{0}}I(a/2)}{2\pi {{a}^{2}}}}{\frac{{{\mu }_{0}}I}{2\pi (2a)}}=1:1\]


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