AMU Medical AMU Solved Paper-2011

  • question_answer
    A 600 pF capacitor is charged by 200 V supply. It is then disconnected from the supply and is connected to another 300 pF capacitor. The electrostatic energy lost in the process is

    A)  zero                                     

    B)  \[4\times {{10}^{-6}}J\]

    C) \[6\times {{10}^{-6}}J\]                                

    D)  \[8\times {{10}^{-6}}J\]

    Correct Answer: C

    Solution :

                     Energy stored in capacitor                 \[{{E}_{1}}=\frac{1}{2}C{{V}^{2}}\]                 \[=\frac{1}{2}\times 600\times {{10}^{-12}}\times {{(200)}^{2}}\]                 \[=12\times {{10}^{-6}}J\] Again \[{{E}_{2}}=\frac{1}{2}(600+300)\times {{10}^{-12}}\times {{(200)}^{2}}\]                 \[=\frac{1}{2}\times 900\times {{10}^{-12}}\times 4\times {{10}^{4}}\]                 \[=18\times {{10}^{6}}J\] Energy lost \[={{E}_{1}}=-{{E}_{2}}\]                 \[=18\times {{10}^{-6}}-12\times {{10}^{-6}}\]                 \[=6\times {{10}^{-6}}J\]


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