NEET Sample Paper NEET Sample Test Paper-3

  • question_answer
    The wire loop formed by join in two semi-circular sections of radii \[{{R}_{1}}\] and \[{{R}_{2}},\] carries a current I, as shown. The magnitude of magnetic field at the centre C is:

    A)  \[\frac{{{H}_{o}}I}{2}\left( \frac{1}{{{R}_{1}}}+\frac{1}{{{R}_{2}}} \right)\]

    B)  \[\frac{{{H}_{o}}I}{4}\left( \frac{1}{{{R}_{1}}}+\frac{1}{{{R}_{2}}} \right)\]

    C)  \[\frac{{{H}_{o}}I}{2}\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]

    D)  \[\frac{{{H}_{o}}I}{4}\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]

    Correct Answer: D

    Solution :

        The magnitude of magnetic field due to circular loop which radius \[{{R}_{1}}\] at centre C is \[{{B}_{1}}=-\frac{{{\mu }_{0}}}{4},\frac{I}{{{R}_{1}}}\] Similarly, for radius \[{{R}_{2}}\]                 \[{{B}_{2}}=\frac{{{\mu }_{0}}}{4},\frac{I}{{{R}_{2}}}\]  (direction of current is opposite). Now the resultant magnitude of magnetic field due to circular loop at the centre C is:             \[B={{B}_{1}}+{{B}_{2}}\] (as magnetic field at C due to straight part of the conductor, will be zero). \[\Rightarrow \]               \[B=\frac{{{\mu }_{0}}}{4},\frac{I}{{{R}_{1}}}-\frac{{{\mu }_{0}}}{4}-\frac{I}{{{R}_{2}}}\]                 \[B=\frac{{{\mu }_{0}}I}{4}\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]


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