# Homework Help: Equivalent Capacitance

1. Mar 10, 2014

### Maylis

1. The problem statement, all variables and given/known data
Reduce the circuit below into a single equivalent capacitor at terminals a,b. Assume all initial voltages at t = 0 are zero.

2. Relevant equations

3. The attempt at a solution

My first thought was to take all the capacitors that to me look to be in parallel and combine them. I said that they are in parallel because they share at least 2 nodes on both sides of the components.

Then, I said the capacitors on the left side are in series. There is a lot of doubt in my decision here. I say that because they all 3 share the same node on only one side of their component, so I called them in series.

Then, after that the rest are clearly in series so I combined them.

Also, I wonder why it matters what terminals I choose to find the equivalent capacitance between, and what would happen if I chose different terminals?

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Last edited: Mar 10, 2014
2. Mar 10, 2014

### PhysicoRaj

Your understanding of series and parallel combination is still wrong. After you combined the parallels, you say the left 3 are in series.. how is that? If you have gone through the thread you have linked, it contains an answer to the trick.

3. Mar 10, 2014

### Maylis

I say they are in series because they all share one node on one side of the component.

4. Mar 10, 2014

### Maylis

Alright, I redid it saying the 2C capacitors were in series. However, how do I know the current is the same? I mean, the charges land on the capacitor and don't go to the other side, is the current on a capacitor the same on both sides of the capacitor for one component?

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5. Mar 10, 2014

### PhysicoRaj

That's where you have gone wrong. Only two of them can share a point in series.

6. Mar 10, 2014

### PhysicoRaj

Yes. That's why it is 'current through a capacitor'

7. Mar 10, 2014