CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    A capacitor of capacitance value\[1\,\mu F\]is charged to 30 V and the battery is then disconnected. If the remaining circuit is connected across a\[2\,\mu F\]capacitor, the energy lost by the system is

    A)  \[300\,\mu J\]          

    B)         \[450\,\mu J\]

    C)  \[225\,\mu J\]          

    D)         \[245.0\,J\]

    E)  \[100\,\mu J\]

    Correct Answer: A

    Solution :

    Energy \[{{E}_{1}}=\frac{1}{2}{{C}_{1}}V_{1}^{2}=\frac{1}{2}\times 1\times {{10}^{-6}}\times {{(30)}^{2}}\] \[=450\times {{10}^{-6}}J\] Common potential                 \[V=\frac{{{q}_{1}}+{{q}_{2}}}{{{C}_{1}}+{{C}_{2}}}\]                 \[=\frac{1\times 30+0}{1+2}=10\,volt\]                 \[{{E}_{2}}=\frac{1}{2}({{C}_{1}}+{{C}_{2}}){{V}^{2}}\]                 \[=\frac{1}{2}(1+2)\times {{10}^{-6}}\times {{(10)}^{2}}\]                 \[=1.5\times 100\times {{10}^{-6}}\]                 \[=150\times {{10}^{-6}}J\] Loss of energy\[={{E}_{2}}-{{E}_{1}}=300\,\mu J\]


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