# Homework Help: Equivalent Capacitors and their charges:

1. Sep 15, 2009

### spriter

1. The problem statement, all variables and given/known data
Hi, I'm trying to solve this problem on MasteringPhysics:

This circuit is given, and it says C-eq for the circuit is 9.22 microfarads:

http://img143.imageshack.us/img143/3475/walker4ech21pr118.jpg [Broken]

The question is to find C in the figure knowing C-eq is 9.22 microfarads.

2. Relevant equations
C-eq series = 1/C-eq = 1/C1 + 1/C2 + ...
C-eq parallel = C1 + C2 + C3 ...

3. The attempt at a solution

At first I tried to take the three center capacitors to be parallel (The 7.22, 4.25, and 8.35) and find the Ceq of them and then take the other two to be in a series with this C-eq. But when I do that, I get a negative value for C.

Then I tried to take the C, 12.0 uF, and 8.35 uF to be in a series, combine them and then have that C-eq be parallel to the other two, but that also gives me a negative value.

Thank you.

Last edited by a moderator: May 4, 2017
2. Sep 15, 2009

### rl.bhat

In the circuit diagram no three capacitors are either series or parallel.
Here 12μF and 8.35μF are in series. Equivalent of these capacitors is in parallel with 4.5 μF.
Combination of these capacitors is in series with C. Finally all the above is in parallel with 7.22 μF. The whole combination is equal to 9.22 μF. Write down the correct equations and solve for C.