# Capacitor Network

1. Feb 13, 2008

### heartofaragorn

1. The problem statement, all variables and given/known data
In this circuit, what is the potential difference across C4? (Please see attached picture)

2. Relevant equations
C= Q / V
Capacitors in parallel: C2345=C2 + C3 + C4 + C5
Capacitors in series: 1/C total = 1/ C1 + ...

3. The attempt at a solution

I have gone over this problem with 2 different professors and have used the online help extensively, and the correct answer cannot be arrived at. What I have gathered from both the professors at the help is the following sequence:
1. Find Ctotal by adding the capacitors in parallel then adding to C1 in series. This gave an answer of 2.053.
2. Find the total Charge by multiplying Ctotal by 12 Volts, as given in the problem. This gives an answer of 24.636.
3. My prof says that the next step is to say that Qtotal = Q1; the online help says to calculate "Cab" next to find the potential difference at the line "ab" in the picture. Neither answer was correct according to the help. If I solved for "Vab", I received an answer of 2.737, which was deemed incorrect.
4. Prof said that V1 = Q1 / C1 (answer was 8.212); online help said that "Vab" is equal to "V34". I'm pretty sure this is where I went wrong, but I don't know how.
5. Prof said that Vab = 12-V1 (solved for in step 4). I received an answer of 3.788.
6. Vab is still equal to V34, so I can see that V34 should equal 3.788. According to the online help, IT DOESN'T.
7. Even with the answer of 3.788, I tried to solve for V4 by using the equation Vab = Q3/C3 + Q4/C4 with Q3 = Q4 since they are in parallel. I solved the equation algebraically and I may have messed up there. I received a final answer of 2.525 Volts...of course, it was wrong.

I have been working on this problem for days and it's making me nuts. Any help would be most appreciated! :yuck:

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