# Homework Help: Energy stored in a single capacitor

1. Oct 18, 2012

### lat77

1. The problem statement, all variables and given/known data
For the capacitor network shown in the Figure (Figure 1) , the potential difference across is 12.0 . (Figure is attached by the way)
A)Find the total energy stored in this network. (I already found this to be 158 μJ)
B)Find the energy stored in the 4.80- capacitor.

2. Relevant equations
U=1/2 CV^2

3. The attempt at a solution
I would imagine that you need to subtract the amount of energy in the parallel branches from the total amount of energy of the system, but I don't know how to do this without knowing the charge.

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2. Oct 18, 2012

### misterc

Another equation that I would add to your list is Q = CV (Charge = Capacitance x voltage).

I will give you a hint in the form of two questions:
1) How are the charges in a series capacitor circuit related?
2) How does the charge on one of the capacitors in a series capacitor circuit related to the total charge in the circuit?

3. Oct 18, 2012

### lat77

1) Q=CV as your equation said.
2) (Qtotal/#of capacitors)=Charge per capacitor?

4. Oct 18, 2012

### misterc

Since you got part a), I'll assume you can convert between series, parallel and total capacitance.

So, in your problem, we can model the circuit as three capacitors in series. Correct?

Let's call the three capacitors C1, C2, C3 where C1 = 8.6 uF, C2 = 4.8 uF, and C3 = 7.5 uF. Correct?

Let's call Ceq the total equivalent capacitance = 2.18 uF. Correct?

My questions then are:
How are Q1, Q2, and Q3 related?
How does Q2 (since that's the capacitor in question), relate to Qeq?