JEE Main & Advanced Physics Electrostatics & Capacitance JEE PYQ-Electrostatics and Capacitance

  • question_answer
    A series combination of\[{{n}_{1}}\] capacitors, each of capacity \[{{C}_{1}}\] is charged by source of potential difference 4 V. When another parallel combination of \[{{n}_{2}}\]capacitors each of capacity \[{{C}_{2}}\] is charged by a source of potential difference V, it has the same total energy stored in it as the first combination has. The value of \[{{C}_{2}}\] in terms of \[{{C}_{1}}\]is then         [JEE ONLINE 12-05-2012]

    A) \[16\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]

    B) \[\frac{2{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]

    C) \[2\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]

    D) \[\frac{16{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]

    Correct Answer: D

    Solution :

    [d] Equivalent capacitance of \[{{n}_{2}}\] number of capacitors each of capacitance \[{{C}_{2}}\] in parallel\[={{n}_{2}}{{C}_{2}}\]
    Equivalent capacitance of\[{{n}_{1}}\] number of capacitors each of capacitances \[{{C}_{1}}\] in series.
    Capacitance of each is \[{{C}_{1}}=\frac{{{C}_{1}}}{{{n}_{1}}}\]
    According to question, total energy stored in both the combinations are same
    i.e.,\[\frac{1}{2}\left( \frac{{{C}_{1}}}{{{n}_{1}}} \right){{\left( 4V \right)}^{2}}=\frac{1}{2}\left( {{n}_{2}}{{C}_{2}} \right){{V}^{2}}\]
    \[\therefore \]\[{{C}_{2}}=\frac{16{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]


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