# Effective Capacitance

1. Jun 28, 2008

### purduegirl

1. The problem statement, all variables and given/known data

Three capacitors of capacitance 8, 9, and 5 μF respectively, are connected in series to a 4 V battery. What is the charge on the positive plate of the 9 μF capacitor?

2. Relevant equations

Q = C*E
1/C = 1/C1 + ..
3. The attempt at a solution

I drew out the circuit it would make. I know that to calculate C it is 1/C = 1/C1+1/C2...
I took the general equation for Q= C*E. I did this and got 1.74 uC. But, this is not correct. Could you tell me where I am going wrong?

2. Jun 29, 2008

### alphysicist

Hi purduegirl,

You calculation of the equivalent capacitance is wrong. Your post does not have many numbers, but you seem to have calculated that the equivalent capacitance was about 0.435 $\mu$F, but that is not what 1/C = 1/C1+1/C2... gives.

Do you see what went wrong, and what the equivalent capacitance should be?