# Capacitors Complicated Circuit

1. Mar 4, 2013

### majormaaz

1. The problem statement, all variables and given/known data
In Fig. 26-32, the battery has a potential difference of 20 V.
http://www.webassign.net/hrw/26_32.gif

2. Relevant equations
If Capacitors are in series, then (1/C1) + (1/C2) = (1/Cnew)
If Capacitors are in parallel, then you just add them, C1 + C2 = Cnew

3. The attempt at a solution
I'm not sure how to get the equivalent capacitance from here.
Would I just add the 12/7 to the 2uF parallel from it to make one capacitor? What happens then to the 2uF originally in series with the 12/7 uF?
This is what I did: Combine the 3 and 4 uF capacs, then the 12/7 and 2 uF(parallel), then that and 3 uF (series) and then that with the remaining 2 uF and 3 uF, in series.
I ended up with 0.696, which is apparently wrong. Is there a correct way how to resolve all these capacitors? PEMDAS for circuits? Any help will be appreciated

2. Mar 4, 2013

### majormaaz

Here's a picture showing where I'm stuck at:

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3. Mar 4, 2013

### phinds

Uh ... how did you get 4 in series with 4 = 12/7 ???

4. Mar 4, 2013

### majormaaz

....Thaaaat appears to be my problem. Thanks! I'll have a go at this again

5. Mar 4, 2013

### majormaaz

So, I did the work again, fixing that 3 uF into a 4 uF, and I ended up with getting 12/17 uF, but that's not right either.
Could somebody advise me as to which branches/capacitors I should deal with first, and so on?

6. Mar 5, 2013

### Staff: Mentor

Are you using a calculator?

It is pretty obvious when capacitors are in series, so you might as well start there. (But it doesn't matter where you start.) Re-draw the circuit after each step.

So you have 2x 4µF in series, what equivalent capacitance is that?

I can see a pair of 3µF in parallel.

7. Mar 5, 2013

### phinds

You need to show your work so we can see how it is that you are getting these nonsensical answers

Show step by step how you reduce two 4-uf's in series to a single equivalent cap.

8. Mar 5, 2013

### majormaaz

I hope this picture helps! It goes from left to right, just in case you didn't know.
EDIT: Sorry, wrong picture

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9. Mar 5, 2013

### majormaaz

Here we go! My REVISED work.

#### Attached Files:

• ###### Capac.png
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10. Mar 5, 2013

### phinds

You KEEP not showing your work, just the end results of each step. Let me repeat myself:

You need to show your work so we can see how it is that you are getting these nonsensical answers

11. Mar 6, 2013

### Staff: Mentor

You overlooked my hint? ("I can see a pair of 3µF in parallel")