NEET Sample Paper NEET Sample Test Paper-55

  • question_answer
    A conducting loop of radius R is present in a uniform magnetic field B perpendicular the plane of the ring. If radius R varies as a function of time ?t?, as \[R={{R}_{0}}+t\]. The e.m.f., induced in the loop is-

    A) \[2\pi ({{R}_{0}}+t)B\]

    B) \[\pi \left( {{R}_{0}}+t \right)B\] clockwise

    C) \[2\pi \left( {{R}_{0}}+t \right)B\] anticlockwise

    D) zero

    Correct Answer: C

    Solution :

    \[e=B\,\,\frac{dA}{dt}\] \[=B\,\,\frac{d}{dt}\,\,=\,\,(\pi {{r}^{2}})\] \[=\,\,B\,\pi \,\frac{d}{dt}\,\,\,{{({{R}_{0}}+t)}^{2}}\] \[=\,\,B\,\pi \,\frac{d}{dt}\,\,\,({{R}_{0}}^{2}+{{t}^{2}}+2\,\,{{R}_{0}}t)\] \[=\,\,B\pi \left( 2t+2{{R}_{0}} \right)\] \[=\text{ }2\pi B\left( t+{{R}_{0}} \right)\] As flux in -ve z direction is increasing hence induced current should be anticlockwise.


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