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Railways RRB (Assistant Loco Pilot & Technician) Solved Paper-2 (2014)

  • question_answer
    The magnetic field at a distance r from a long wire carrying current i is \[0.4\] tesla. The magnetic field at a distance 2 r is

    A)  \[0.2\]tesla                  

    B)  \[0.8\]tesla

    C)  \[0.1\]tesla                  

    D)  \[1.6\]tesla

    Correct Answer: A

    Solution :

    \[B=\frac{{{\mu }_{0}}i}{2\pi r}\Rightarrow 0.4=\frac{{{\mu }_{0}}i}{2\pi r}\] \[B'=\frac{{{\mu }_{0}}i}{2\pi (2r)}=\frac{1}{2}\frac{{{\mu }_{0}}i}{2\pi r}=\frac{1}{2}\times 0.4=0.2\]tesla


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