NEET Sample Paper NEET Sample Test Paper-82

  • question_answer
    Circular loop of a wire and a long straight wire carry currents\[{{I}_{c}}\,and\,\,{{I}_{e}}\], respectively as shown in figure. Assuming that these are placed in the same plane. The magnetic field will be zero at the centre of the loop when the separation H is

    A)  \[\frac{{{I}_{e}}R}{{{I}_{c}}\pi }\]                             

    B)  \[\frac{{{I}_{c}}R}{{{I}_{e}}\pi }\]

    C)  \[\frac{\pi {{I}_{c}}}{{{I}_{e}}R}\]                             

    D)  \[\frac{{{I}_{e}}\pi }{{{I}_{c}}R}\]  

    Correct Answer: A

    Solution :

    Magnetic field at the centre O of the loop of radius is \[{{B}_{1}}=\frac{{{\mu }_{0}}lc}{2R}\] Magnetic field due to the straight wire at the centre is \[{{B}_{2}}=\frac{{{\mu }_{0}}le}{2\pi H}\] For net field to be zero \[{{B}_{1}}={{B}_{2}}\,\,\,\Rightarrow \,\,\frac{{{\mu }_{o}}{{l}_{c}}}{2R}=\frac{{{\mu }_{o}}{{l}_{e}}}{2\pi H}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,H=\frac{{{l}_{e}}R}{\pi {{l}_{c}}}\]


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