# RC Circuit 2

1. Oct 1, 2009

### deerhunt713

Three resistors and a capacitor are in a circuit with a battery:
R1 = 23 Ω
R2 = 13 Ω
R3 = 15 Ω
C = 6.2 µF
V = 17 V
The switch has been closed for a long time. What will the charge be on the capacitor 195 μs after the switch is opened?

picture
https://online-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/fall09/homework/06/11_paired/image.gif [Broken]
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 4, 2017
2. Oct 1, 2009

### kuruman

WHat are your thoughts on the matter? Is this a charging or discharging capacitor 195 μs after the switch is opened? What are the relevant equations to describe this?

3. Oct 4, 2009

### deerhunt713

ok well the capacitor is fully charged, so the voltage of the capacitor is the same as the battery, from there i can find the max charge. then i used the equation Qmax(1-e^(t/CR))
where i used 28 for the resistance. but thats not giving me the right answer

4. Oct 4, 2009

### kuruman

Try again. The voltage across the capacitor is the same as across the series combination R2+R3. That's not the voltage across the battery. What is it?

5. Oct 5, 2009

### willem2

That's not the only problem. The current through C is not the current through either R1 or R2+R3 so you can't use those in Qmax(1-e^(t/CR) either.

I recommend replacing V, R1, R2 and R3 with their Thevenin equivalent.