JEE Main & Advanced Physics Alternating Current / प्रत्यावर्ती धारा Question Bank Self Evaluation Test - Alternating Current

  • question_answer
    The current in an L-R circuit builds up to\[{{(3/4)}^{th}}\]of its steady state value in 4 seconds. The time constant of this circuit is

    A) \[\frac{1}{ln\,\,2}\sec \]

    B) \[\frac{2}{ln\,\,2}\sec \]

    C) \[\frac{3}{ln\,\,2}\sec \]

    D) \[\frac{4}{ln\,\,2}\sec \]

    Correct Answer: B

    Solution :

    [b] \[I={{I}_{0}}(I-{{e}^{-t/\tau }})\] where \[\tau \to \] time constant \[\therefore \,\,\,\,\frac{3}{4}{{I}_{0}}={{I}_{0}}(1-{{e}^{-t/\tau }})\Rightarrow \frac{3}{4}=l-{{e}^{-t/\tau }}\] \[\Rightarrow \,\,{{e}^{-t/\tau }}=\frac{1}{4}\] \[\,\Rightarrow \,\,\,\frac{-t}{\tau }\] In \[e=In\,\frac{1}{4}\Rightarrow \frac{-4}{\tau }=-2\] In \[2\Rightarrow \tau =\frac{2}{In\,\,\,2}\]


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