JCECE Engineering JCECE Engineering Solved Paper-2004

  • question_answer
    If the condenser shown in the circuit is charged to \[5\,\,V\] and left in the circuit, in \[12\,\,s\] the charge on the condenser will become:

    A) \[\frac{10}{e}coulomb\]                              

    B) \[\frac{{{e}^{2}}}{10}coulomb\]

    C)  \[\frac{10}{{{e}^{2}}}coulomb\]                              

    D)  \[\frac{e}{10}coulomb\]

    Correct Answer: A

    Solution :

    Key Idea: Exponential decay of charge takes place. In a \[C\text{-}R\] circuit, discharging takes place. The \[q\text{-}t\] equation is                 \[q={{q}_{0}}{{e}^{-t/RC}}\] where \[R\] is resistance, \[C\] is capacitance and\[{{q}_{0}}=C{{V}_{0}}\] Hence,  \[q=C{{V}_{0}}{{e}^{-t/RC}}\] Given,   \[{{V}_{0}}=5V,\,\,C=2F,\,\,t=12s,\,\,R=6\Omega \] \[\therefore \]  \[q=2\times 5{{e}^{-12/6\times 2}}=\frac{10}{e}\]coulomb


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