# Homework Help: Two Capacitor problem

1. May 14, 2014

### Vibhor

1. The problem statement, all variables and given/known data

Two capacitors $C_1$ and $C_2$ (where $C_1 > C_2$) are charged to the same initial potential difference $V_i$, but with opposite polarity. The charged capacitors are removed from the battery, and their plates are connected as shown in Figure a. The switches $S_1$ and $S_2$ are then closed, as shown in Figure b. Find the final potential difference $V_f$ between a and b after the switches are closed

2. Relevant equations

3. The attempt at a solution

Let Vf be final potential difference.

$V_f = \frac{Q_{1f}}{C_1} = \frac{Q_{2f}}{C_2}$
$Q_1-Q_2 = Q_{1f}+Q_{2f}$
$Q_1-Q_2 = Q_{1f}+\frac{C_2}{C_1}Q_{1f}$
$C_1V_i-C_2V_i = \frac{C_1+C_2}{C_1}Q_{1f}$

$V_f = \frac{C_1-C_2}{C_1+C_2}V_i$

Is this correct ?

#### Attached Files:

• ###### Cap.GIF
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2. May 15, 2014

### ehild

Yes.

ehild

3. May 16, 2014

### Vibhor

Many thanks ehild :)