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WB JEE Medical WB JEE Medical Solved Paper-2006

  • question_answer
    The magnetic flux linked with a coil at any instant t is given by the equation : \[\text{o }\!\!|\!\!\text{ =}\,\text{5}{{\text{t}}^{3}}-100t+300.\]The magnitude of emf induced in the coil after 3 s is :

    A)  10 V                                     

    B)  20 V

    C)  35 V                                     

    D)  70 V

    Correct Answer: C

    Solution :

                     Given, \[\text{o }\!\!|\!\!\text{ =}\,\text{5}{{\text{t}}^{2}}-100t+300\] \[\therefore \]  \[e=-\frac{d\text{o }\!\!|\!\!\text{ }}{dt}\] \[=\frac{-d}{dt}(5{{t}^{3}}-100t+300)\]                 \[=-(15{{t}^{2}}-100+0)\] \[=-15{{t}^{2}}+100\]                 \[\therefore \]  \[\frac{e}{t}=-15{{(3)}^{2}}+100\]                                 \[=-15\times 9+100\] \[=-135+100\] \[=-35\,V\] Minus sign signifies the Lenzs law.


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