Calculating Capacitance and Charge in Connected Capacitors

[tag16]

Homework Statement

Four capacitors are connected as shown here: http://i4.photobucket.com/albums/y103/thepastryman/HWa.jpg (a) Find the equivalent capacitance between points a and b (b) Calculate the charge on each capacitor, taking delta Vab= 15.0V

note: the actual numbers are not the same as those in the diagram. Stating from the top moving from left to right they are: 15.0 micro farads, 3 micro farads, 20 micro farads and 6 micro farads

Homework Equations

parallel: Ceq= C1+C2

series: Ceq=1/C1+1/C2

The Attempt at a Solution

I just used the above equations to find part a, is that right? For part b, would you just use Q=cv or is it more involved then that?

 

[willem2]

I just used the above equations to find part a, is that right? For part b, would you just use Q=cv or is it more involved then that?

I hope you used $$\frac{1}{C_{eq}}= \frac{1}{C_1}+\frac{1}{C_2}$$

if you have 2 parallel capacitors you can just use Q = CV for both of them.

If you have 2 series capacitors, you need the fact the charge of a both of the capacitors is equal to the charge on their equivalent capacitors. (because the same current goes through all of them)
This also assumes all capacitors started uncharged.

 

[tag16]

This is what I did for part a: (1/C1+1/C2)^-1= (1/15microF+1/3microF)^-1= 1.42x10^-7

Ceq= 6microF+20microF+1.42x10^-7

is that right?

For part b I know for series capacitors that the charges are all equal I just don't know how that would effect the set up to my equation to solve the problem.