JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Grouping of Capacitors

  • question_answer
    . A capacitor \[4\mu F\]charged to 50 \[V\] is connected to another capacitor of \[2\mu F\] charged to 100 \[V\] with plates of like charges connected together. The total energy before and after connection in multiples of  \[({{10}^{-2}}J)\] is  [MP PMT 1992]

    A)                    1.5 and 1.33                  

    B)            1.33 and 1.5

    C)                    3.0 and 2.67                  

    D)            2.67 and 3.0

    Correct Answer: A

    Solution :

                       The total energy before connection                    \[=\frac{1}{2}\times 4\times {{10}^{-6}}\times {{(50)}^{2}}+\frac{1}{2}\times 2\times {{10}^{-6}}\times {{(100)}^{2}}\]                    \[=1.5\times {{10}^{-2}}J\]                    When connected in parallel                    \[4\times 50+2\times 100=6\times V\] Þ \[V=\frac{200}{3}\]                    Total energy after connection                    \[=\frac{1}{2}\times 6\times {{10}^{-6}}\times {{\left( \frac{200}{3} \right)}^{2}}=1.33\times {{10}^{-2}}J\]


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