JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव JEE PYQ-Magnetic Effects Of Current

  • question_answer
    Consider two thin identical conducting wires covered with very thin insulating material. One of the wires is bent into a loop and produces magnetic field \[{{B}_{1}},\] at its centre when a current I passes through it. The ratio \[{{B}_{1}}:{{B}_{2}}\] is:          [JEE ONLINE 12-04-2014]

    A) 1 : 1

    B) 1 : 3

    C) 1 : 9

    D) 9 : 1

    Correct Answer: B

    Solution :

    [b] For loop 0nI\[B=\frac{{{\mu }_{0}}nI}{2a}\]where, a is the radius of loop.
    Then, \[{{B}_{1}}=\frac{{{\mu }_{0}}I}{2a}\]
    Now, for coil \[B=\frac{{{\mu }_{0}}I}{4\pi }.\frac{2nA}{{{x}^{3}}}\]
    at the centre x = radius of loop
    \[{{B}_{2}}=\frac{{{\mu }_{0}}}{4\pi }.\frac{2\times 3\times \left( I/3 \right)\times \pi {{\left( a/3 \right)}^{2}}}{{{\left( a/3 \right)}^{3}}}\]
    \[=\frac{{{\mu }_{0}}.3I}{2a}\]
    \[\therefore \]\[\frac{{{B}_{1}}}{{{B}_{2}}}=\frac{{{\mu }_{0}}I/2a}{{{\mu }_{0}}.3I/2a}\]\[{{B}_{1}}:{{B}_{2}}=1:3\]


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