# Help distinguishing between series and parallel capacitors

• paulrb
In summary, the conversation discusses the rules for combining capacitors in series and parallel. The speaker struggles with understanding when to combine in series and when to combine in parallel, but they find a trick to help them determine this. The trick involves being able to go from one terminal of the first element to one terminal of the second element without crossing a junction in the wire. The conversation also clarifies that for parallel, there are two conditions that must be satisfied: being able to go from both terminals of the first element to both terminals of the second element without crossing a junction. The question is then raised if there can be a circuit that is neither series nor parallel.
paulrb
Edit: I found out how to solve this but I'd still appreciate some tips (see bottom).

## Homework Equations

Capacitors in series:
Q = Q1 = Q2 = ...
V = v1 + v2 + ...
1/Ceq = 1/C1 + 1/C2 + ...

Capacitors in parallel:
Q = Q1 + Q2 + ...
V = V1 = V2 = ...
Ceq = C1 + C2 + ...

## The Attempt at a Solution

I tried combining the capacitors C1 and C2 on the left and right sides together in parallel, but apparently that is not correct. I have trouble understanding when to combine in series and when to combine in parallel. It says to combine in parallel if the capacitors appear to be connected like the rungs of a ladder. In this problem, they appear to be connected like the rungs of a ladder, yet they are in series.

Is there some "trick" to understanding when to combine in parallel and when to combine in series? Thanks for your help.

Edit: Upon searching more in this forum, I found a post where someone said capacitors are only in parallel if there is nothing between the capacitors except wire. So in this case, C3 is between C1 and C2, thus C1 and C2 cannot be parallel. Is this correct? If so, I would solve by combining C1 and C2 in series on each side, then combining those with C3 in parallel. Also on the bottom, combine C2 and C2 in parallel, then combine that result with the previous result in series. I did that, and got the right answer. However, if there's any kind of tricks you use to understand how to combine capacitors, I would appreciate it if you'd still share them.

Last edited:
L_landau
paulrb said:
Edit: I found out how to solve this but I'd still appreciate some tips (see bottom).

## Homework Equations

Capacitors in series:
Q = Q1 = Q2 = ...
V = v1 + v2 + ...
1/Ceq = 1/C1 + 1/C2 + ...

Capacitors in parallel:
Q = Q1 + Q2 + ...
V = V1 = V2 = ...
Ceq = C1 + C2 + ...

## The Attempt at a Solution

I tried combining the capacitors C1 and C2 on the left and right sides together in parallel, but apparently that is not correct. I have trouble understanding when to combine in series and when to combine in parallel. It says to combine in parallel if the capacitors appear to be connected like the rungs of a ladder. In this problem, they appear to be connected like the rungs of a ladder, yet they are in series.

Is there some "trick" to understanding when to combine in parallel and when to combine in series? Thanks for your help.

Edit: Upon searching more in this forum, I found a post where someone said capacitors are only in parallel if there is nothing between the capacitors except wire. So in this case, C3 is between C1 and C2, thus C1 and C2 cannot be parallel. Is this correct? If so, I would solve by combining C1 and C2 in series on each side, then combining those with C3 in parallel. Also on the bottom, combine C2 and C2 in parallel, then combine that result with the previous result in series. I did that, and got the right answer. However, if there's any kind of tricks you use to understand how to combine capacitors, I would appreciate it if you'd still share them.

The trick is this:

If you want to see if two circuit elements are in series (this applies to capacitors, resistors, anything): try the following:

If you can get from one terminal (one side) of the first element to one terminal of the second element without ever crossing a junction in the wire (a point where two or more wires connect), then those two elements are in series. It does not matter if along the way you go through another circuit element (a battery, a resistor, a capacitor, etc), as long as you don't cross a junction. You don't have to be able to do that for both terminals of the two elements. As long as you can get from one of the terminals fo the first element to one of the terminals of the second element without crossing ajunction, they are in series.

Thank you, that really clears a lot up for me. But just to clarify: is the reverse of that true as well? - If you cross a junction no matter which side you choose, the capacitors/resistors/etc. must be in parallel.

paulrb said:
Thank you, that really clears a lot up for me. But just to clarify: is the reverse of that true as well? - If you cross a junction no matter which side you choose, the capacitors/resistors/etc. must be in parallel.

No, it's a bitmore involved for parallel.

You have to satisfy two conditions. You must be able to go from one terminal of the first element to a terminal of the second element without crossing any other circuit element but while crossing one junction AND you must be able to do the same for the second terminal (you must be able to get from the second terminal of teh first element to the second terminal fo the second element without crossing any other circuit element but while crossing a junction).

For the series, there is only one condition. But for parallel, the two terminals must satisfy the rule.

I have a question based on this. Can there be a circuit that is neither series or parallel? Such as if there conditions for parallel held for one terminal of the first element, but for the other terminal, there are 2 junctions and another circuit element in the path to the second terminal of the second element?

Last edited:
gwingfan2 said:
I have a question based on this. Can there be a circuit that is neither series or parallel? Such as if there conditions for parallel held for one terminal of the first element, but for the other terminal, there are 2 junctions and another circuit element in the path to the second terminal of the second element?

It's a difficult topology to imagine as a circuit element will necessarily connect between 2 nodes of a circuit. If you have a single loop then the elements will necessarily be connected in a string or in series. Once you have multiple loops then you must give consideration to the Kirchhoff and Ohms law considerations. Of course you can always simply circuits with equivalent substitutions, but ultimately these are all derived from the solutions to the circuit equations aren't they?

Attached is a sample circuit, also, note that all the capacitors have equal capacitance except fot the one on the top left, which is less than the others.

#### Attachments

• circuit.txt
254 bytes · Views: 546

## 1. What is the difference between series and parallel capacitors?

In series capacitors, the capacitors are connected end-to-end, with the positive terminal of one capacitor connected to the negative terminal of the next. In parallel capacitors, the capacitors are connected side-by-side, with all positive terminals connected together and all negative terminals connected together.

## 2. How does the capacitance change in series and parallel capacitors?

In series capacitors, the total capacitance is equal to the reciprocal of the sum of the reciprocals of each individual capacitor's capacitance. In parallel capacitors, the total capacitance is equal to the sum of each individual capacitor's capacitance.

## 3. Which configuration is better for increasing the overall capacitance?

Parallel capacitors are better for increasing the overall capacitance as the total capacitance is simply the sum of the individual capacitances. In series capacitors, the total capacitance will always be less than the capacitance of any individual capacitor.

## 4. How does the voltage change in series and parallel capacitors?

In series capacitors, the voltage is divided among the capacitors, with each capacitor having a different voltage. In parallel capacitors, the voltage across each capacitor is the same as the voltage across the entire circuit.

## 5. Which configuration is better for handling high voltage?

In terms of voltage handling, series capacitors are better as the voltage is divided among the capacitors, reducing the voltage across each capacitor. This means that each capacitor only needs to handle a fraction of the total voltage. In parallel capacitors, each capacitor must handle the full voltage of the circuit, making it more susceptible to breakdown.

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