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J & K CET Engineering J and K - CET Engineering Solved Paper-2013

  • question_answer
    A parallel plate capacitor of capacitance 5 microfarad is charged to \[120\text{ }V\]and then connected to another uncharged  capacitor. If the potential falls to \[40\text{ }V,\] and capacitance of the second capacitor is

    A)  5 microfarad      

    B)  10 microfarad

    C)  15 microfarad     

    D)  20 microfarad

    Correct Answer: C

    Solution :

    Change, \[Q=CV\] Given,  \[C=5\mu F=5\times {{10}^{-6}}F,\,V=120V\] \[Q=5\times {{10}^{-6}}\times 120\] Also, \[5\times {{10}^{-6}}\times 120=40\times C\] \[\Rightarrow \] \[C=\frac{5\times {{10}^{-6}}\times 120}{40}=15\times {{10}^{-6}}F\] \[\Rightarrow \] \[C=15\,\mu F\]


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