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Are C1, C2 and C3 connected in parallel, or C2, C3 in parallel and C1 in series with C23?

Btw it appeared as a question in the basic physics Albanian A-levels yesterday. You had to find the equivalent capacitance, given C1 , C2 and C3.

EDIT: Recently some users are saying the three capacitors are in parallel, which opposes the official answer issued by the test makers (that is C1 in series with C23). Since I don't know the exact answer, please be more specific in your explanations on why it should be as you think it is. And this wasn't my test by the way, I'm just curious to see what its general difficulty is. :D

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3 Answers

up vote 7 down vote accepted

The three capacitors are connected in parallel. There are only two nodes in this circuit. A series connection requires at least three. The equivalent capacitance is just the sum of the three capacitances.

UPDATE: The circuit can be redrawn such that the parallel connection is manifest.

redraw

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Does your answer that the three of them are in parallel go with my idea I have commented at @dingo_d 's? – menislici Jul 1 '12 at 13:47
See the redrawn schematic I've added to my answer – Alfred Centauri Jul 1 '12 at 14:34
Yeah, that's what I thought too. If I had taken the test, I would have done it this way (yours), but the official answer I downloaded from the government website had it the other way, which puzzled me. I don't know if it's just their mistake though. However, Is there a fixed, standard way of determining whether a connection is in parallel or series? Could you point out any link that explains that? After this I even started to doubt my skills in such a basic thing... – menislici Jul 1 '12 at 14:43
If two circuit elements are connected in series then all of the current through one element is through the other, i.e., there is only one path for current through the two elements. If this isn't so, they aren't connected in series. If two circuit elements are connected in parallel, then the same (same as in identical, not same as in equal) voltage is across both circuit elements. – Alfred Centauri Jul 1 '12 at 15:13
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No No No, you can see that alla capacitors are connected in parallel. In fact, what you have to do is to start from a node and follow the branches. I mean start from a node and when you encounter a divergence that's parallel, otherwise that's serial connection, until you reach the ending node. Sorry for my bad English, hope you got the idea.

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Hmm start from a node and fol? I don't get it. Could you be more specific please? – menislici Jul 1 '12 at 13:48
Sorry, obviously I was writing somewhere else, comment updated. – Moussâb Jul 1 '12 at 14:28
up vote -2 down vote

I would say that C1 is connected in series with C23, which are connected in parallel...

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Actually I looked up the answers this morning and your answer was correct. Still I'm somehow baffled because if c1 would be a little more on the left, that is in the last vertical wire, the situation would look like 3 capacitors in parallel. Would moving C1 cause such a difference? – menislici Jul 1 '12 at 9:35
No I don't think that it would. The way I saw it, you start at the first one, and go along the wire, and look at how they 'branch'. You would still start at C1 and see that there is a branching that goes to the C2 and C3. You are actually using Kirchoff's circuit law. – dingo_d Jul 1 '12 at 9:43
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I adamantly disagree. – DJBunk Jul 1 '12 at 23:06
Yeah, I see now, I didn't start at the node, which was my mistake. If you start at the node than you get parallel connection... – dingo_d Jul 2 '12 at 17:35

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