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Manipal Engineering Manipal Engineering Solved Paper-2011

  • question_answer
    A solenoid has an inductance of 60 H and a resistance of 30\[\Omega \]. If it is connected to a 100 V battery, how long will it take for the current to reach \[\frac{e-1}{e}\]= 63.2% of its final value?

    A)  1 s                                         

    B)  2 s

    C)  e second            

    D)         2 e second

    Correct Answer: B

    Solution :

    Given,\[L=60\,\,H\] \[R=30\Omega\] \[V=100V\] In\[L\text{-}R\]circuit current to reach 63.2% of its final value in time constant. Equation of current in\[L\text{-}R\]circuit                 \[I={{I}_{0}}(1-{{e}^{-Rt/L}})\] Required time = time constant                 \[=\frac{L}{R}=\frac{60}{30}=2s\]


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