JEE Main & Advanced JEE Main Paper (Held On 12 May 2012)

  • 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 Main Online Paper (Held On 12 May 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 :

                    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 samei.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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