JEE Main & Advanced JEE Main Paper (Held On 15 April 2018) Slot-II

  • question_answer
    At the centre of a fixed large circular coil of radius \[R\], a much smaller circular coil of radius \[r\] is placed. The two coils are concentric and are in the same plane. The larger coil carries a current \[I\]. The smaller coil is set to rotate with a constant angular velocity \[\omega \] about an axis along their common diameter. Calculate the emf induced in the smaller coil after a time \[t\] of its start of rotation. [JEE Online 15-04-2018 (II)]

    A)                     \[\frac{{{\mu }_{0}}I}{2R}\omega {{r}^{2}}\sin \omega t\]           

    B) \[\frac{{{\mu }_{0}}I}{4R}\omega \pi {{r}^{2}}\sin \omega t\]     

    C) \[\frac{{{\mu }_{0}}I}{2R}\omega \pi {{r}^{2}}\sin \omega t\]

    D)          \[\frac{{{\mu }_{0}}I}{4R}\omega {{r}^{2}}\sin \omega t\]

    Correct Answer: C

    Solution :

    \[\phi =\overline{B}.\overline{A}=BA\cos wt=\pi {{r}^{2}}b\cos wt\] \[\in =-\frac{d\phi }{dt}\] \[=-\frac{d}{dt}(\pi {{r}^{2}}B\cos wt)\] \[=\pi {{r}^{2}}B\sin wt(w)\] \[=\frac{{{\mu }_{o}}I}{2R}\pi w{{r}^{2}}\sin \,\,wt\left( \therefore B=\frac{{{\mu }_{o}}I}{2R} \right)\]


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