BCECE Engineering BCECE Engineering Solved Paper-2008

  • question_answer
    The inductance of a coil is \[L=10\,H\]and resistance \[R=5\,\Omega .\]If applied voltage of battery is 10 V and it switches off in 1 millisecond, find induced emf of inductor,

    A) \[2\times {{10}^{4}}V\]                

    B)  \[1.2\times {{10}^{4}}V\]

    C)  \[2\times {{10}^{-4}}V\]              

    D)         None of these

    Correct Answer: A

    Solution :

    Amount of magnetic flux linked with inductor is \[\phi =Li\] Now, the emf induced-in the inductor is given by \[e=-\frac{d\phi }{dt}=-\frac{d}{dt}(Li)\] \[=-L\frac{di}{dt}\]                 or            \[|e|=L\frac{di}{dt}\] Here, induced current \[=\frac{V}{R}\]                                                 \[=\frac{10}{5}\] \[=2A\] Circuit switches off in 1 millisecond or            \[dt=1\times {{10}^{-3}}s\] and        \[L=10\,H\] \[\therefore \] Induced emf in inductor is         \[|e|=10\times \frac{2}{1\times {{10}^{-3}}}\] \[=2\times {{10}^{4}}V\]


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