How Do You Determine the Equivalent Capacitance in Complex Circuits?

[gfd43tg]

Homework Statement

Reduce the circuit below into a single equivalent capacitor at terminals a,b. Assume all initial voltages at t = 0 are zero.

Homework Equations

The Attempt at a Solution

Okay, this is the circuit I had in mind when I made this thread earlier
https://www.physicsforums.com/showthread.php?p=4684447#post4684447

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?

 

[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.

 

[gfd43tg]

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

 

[gfd43tg]

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?

 

[PhysicoRaj]

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

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

 

[PhysicoRaj]

is the current on a capacitor the same on both sides of the capacitor for one component?

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

 

[CWatters]

Maylis - Your answer in #4 looks correct.

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?

Yes. Electrons going I one side repel electrons out of the other side.