A series combination of $n_1$ capacitors, each of capacity $C_1$ is charged by source of potential…

A series combination of $n_1$ capacitors, each of capacity $C_1$ is charged by source of potential difference $4 \mathrm{~V}$. 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
  1. $16 \frac{n_2}{n_1} C_1$
  2. $\frac{2 C_1}{n_1 n_2}$
  3. $2 \frac{n_2}{n_1} C_1$
  4. $\frac{16 C_1}{n_1 n_2}$

Solution

Equivalent capacitance of $n_2$ number of capacitors each of capacitance $\mathrm{C}_2$ in parallel $=n_2 C_2$ Equivalent capacitance of $n_1$ number of capacitors each of capacitances $\mathrm{C}_1$ 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 $ \begin{aligned} & \text { i.e., } \frac{1}{2}\left(\frac{C_1}{n_1}\right)(4 V)^2=\frac{1}{2}\left(n_2 C_2 \text { b }^2\right. \\ & \therefore C_2=\frac{16 C_1}{n_1 n_2} \\ & \end{aligned} $

Asked in: JEE Main 2012 (12 May Online)

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