NEET Sample Paper NEET Sample Test Paper-20

  • question_answer
    In the circuit shown the cells are ideal and of equal emfs, the capacitance of the capacitor is C and the resistance of the resistor is R. X is first joined to Y and then to Z. After a long time, the total heat produced in the resistor will be

    A)  equal to the energy finally stored in the capacitor.

    B)  half of the energy finally stored in the capacitor.

    C)  twice the energy finally stored in the capacitor.

    D)  4 times the energy finally stored in the capacitor.

    Correct Answer: D

    Solution :

    The charge on the capacitor will charge from \[-\varepsilon C\]to \[\varepsilon C\]where \[\varepsilon =emf\]of each cell. \[\therefore \]Total charge flowing through cell \[B=2\varepsilon C.\] Work done by battery \[B={{w}_{b}}=\varepsilon (2\varepsilon c)=2c{{\varepsilon }^{2}}\] Final energy stored in the capacitor\[=E=\frac{1}{2}C{{\varepsilon }^{2}}\] From Energy conservation law, we get \[{{W}_{b}}-\]Heat produced = change in the energy stored in the capacitor \[\therefore \]\[2C{{\varepsilon }^{2}}-\]heat produced \[=\frac{1}{2}C{{\varepsilon }^{2}}-\frac{1}{2}C{{\varepsilon }^{2}}=0\] \[\Rightarrow \]\[2C{{\varepsilon }^{2}}-\]Heat produced = 0 \[\Rightarrow \]Heat produced \[=2C{{\varepsilon }^{2}}\] \[\therefore \]heat produced \[=2C{{\varepsilon }^{2}}=4E\] Hence, the correction option is (d).


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