# Capacitor Circuit

1. Dec 9, 2009

### 1st1

Capacitor Circuit: Is My Method Correct?

1. The problem statement, all variables and given/known data
Four capacitors, a battery and a switch are assembled in the circuit below. Initially, the switch is set to position A and C4 is uncharged.
At t = 0, the switch is moved to B.
Find Q4, the charge on C4 when the switch is on B.
http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam1/fa09/fig20.gif [Broken]

2. Relevant equations
Q= CV

3. The attempt at a solution

The initial charge on the C3 capacitor = C3 * V1

Now as the switch to moves to B.

The total charges remains the same, but the voltage changes.

Then

Q = ( C3 + C4 ) V2

V2 = Q / ( C3 + C4 )

next with V2 found

Q4 = C4 V2

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Ok, so that is the only way i've been able to figure this out, however, arent the capacitors in series? In that case I would have to change the equivalent capacitance equation to 1/(1/C3+1/C4) which doesn't work out. Can someone please explain whats going on?
Help would be greatly appreciated. Thanks in advance!

Last edited by a moderator: May 4, 2017
2. Dec 10, 2009

### Stonebridge

The question doesn't quite make sense at the moment.
Is the switch first connected to A, and then to B?

3. Dec 10, 2009

### 1st1

Yes, I'm sorry its a three part question and I forgot the main part of the question statement. Fixed now.

Last edited: Dec 10, 2009
4. Dec 10, 2009

### 1st1

Anyone able to help? I've got the answer, I just wanna know if I am doing it correctly and whether the capacitors are considered to be in parallel or in series and why.

5. Dec 11, 2009