Series & Parallel Capacitors: How to Tell?

[Instinctlol]

Hi,
I was wondering how you can tell if 2 capacitor is in series or parallel with each other? I have seen some configuration where it looks like they are in parallel but they are not. Is there any specific way to tell?

 

[PeterO]

Hi,
I was wondering how you can tell if 2 capacitor is in series or parallel with each other? I have seen some configuration where it looks like they are in parallel but they are not. Is there any specific way to tell?

I would be interested to see a picture of that circuit.

I hope you are not getting confused by calculating overall capacitance - it is the opposite formula of resistors.

ie resistors in Series R = R₁ + R₂ + R₃.

Capacitors in Parallel C = C₁ + C₂ + C₃

WHEREAS

Resistors in parallel 1/R = 1/R₁ + 1/R₂ + 1/R₃

Capacitors in series 1/C = 1/C₁ + 1/C₂ + 1/C₃
I

 

[Instinctlol]

I thought C₃ and C₄ are in parallel but they are in series. What makes it in series?

In this picture, I think that C₁ and C₃ are in parallel because the ends are connected to the same potential V_a (points a and b is V_ab). Is this correct?

If you can explain it in a way that relates to my reasoning, that would be great. Thank you!

 

[PeterO]

I thought C₃ and C₄ are in parallel but they are in series. What makes it in series?

In this picture, I think that C₁ and C₃ are in parallel because the ends are connected to the same potential V_a (points a and b is V_ab). Is this correct?

If you can explain it in a way that relates to my reasoning, that would be great. Thank you!

example 1: C₃ and C₄ are in series on their little branch - the path goes through C₃ and then through C₄.

If we begin at the common connection of C₃ and C₄ ; the Right hand side of your picture ; then if you pass from there, through either capacitor, you do NOT end up at the came point electrically speaking - C₂ gets in the way.

If you re-draw the first circuit with points a and b on each side [like example 2] rather than both on the left with the circuit looping round, it will be much clearer I feel.

That re-drawing of complicated circuits in a straight line can make it muck clearer.


Example 2.
Assuming your connection from d to c represents just a wire, then C₁ and C₃ are in parallel with each other, and C₂ and C₄ are in parallel with each other

 

[Instinctlol]

.

If we begin at the common connection of C₃ and C₄ ; the Right hand side of your picture ; then if you pass from there, through either capacitor, you do NOT end up at the came point electrically speaking - C₂ gets in the way.

What do you mean when you say end up at the same point?

 

[PeterO]

What do you mean when you say end up at the same point?

Try this

If you imaging the two junctions in the circuit are labelled d at the top and c at the bottom, then if you leave d, passing through C₃, the only way to c is to pass through C₄ also, showing they are in series.
Note that C₂ is in parallel with that pair, as passing through C₂ is the alternate way to get to that point c

 

[PeterO]

What do you mean when you say end up at the same point?

I forgot; I didn't say the same point, I said the same point electrically.

In your example 2, points c and d are electrically the same - they are connected by a piece of wire.

 

[Instinctlol]

So let me try to summarize, if anything is connected with the same wire (no other potential is involved), it is series. In example 2, C₁ and C₂ are NOT in series because of the wire_cd.

And something is connected parallel if the same potential enters such as C₂ and C₄ in example 2.

 

[PeterO]

So let me try to summarize, if anything is connected with the same wire (no other potential is involved), it is series. In example 2, C₁ and C₂ are NOT in series because of the wire_cd.

And something is connected parallel if the same potential enters such as C₂ and C₄ in example 2.

Reasonable description - certainly in example 2, C₁ and C₂ are NOT in series.

You could re-draw Example 2 as a circuit with two hexagons with each having a flat top and bottom, and sloping sides.

a is the side vertex of the left hexagon, the two hexagons touch at the centre vertex, and b is the right hand vertex of the right hexagon.

C₁ is in the top side of the left hexagon
C₃ is in the bottom side of the left hexagon
C₂ is in the top side of the right hexagon
C₄ is in the bottom side of the right hexagon

drawn that way, the parallel/series relation between the components is obvious; the left hand parallel connection is in Series with the right hand parallel connection.

 

[Instinctlol]

I think I understand now, thanks a lot!

 

[PeterO]

I thought C₃ and C₄ are in parallel but they are in series. What makes it in series?

If you can explain it in a way that relates to my reasoning, that would be great. Thank you!

Describing this circuit starting at a.

First you pass through C₁ [so C₁ is in series with the rest of the circuit.

You then have a choice of passing through C₂ or C₃, so those two are potentially in parallel.
If you choose the C₃ path, then you must continue through C₄, showing that C₃ and C₄ are in series with each other.
You then get to a junction wher the parallel branches finish, so C₂ was in parallel with the C₃ / C₄ combination.
The only place to go now is through C₅, so like C₁, it is in series with the rest of the circuit.

 

[Instinctlol]

Here is a more complicated problem. Did I do this correctly?

 

[Instinctlol]

I think instead of doing the parallel first on the bottom, I think it would be correct to do it in series then parallel

 

[PeterO]

Here is a more complicated problem. Did I do this correctly?

Bottom left,

The 16 & 24 are in series with each other (net 9.8 )
The 24 & 6 are in series with each other (net 4.8 )

Those two combinations are in parallel with each other (net 14.6)

Top example:
The 9 & 15 are certainly in parallel
The 4,8&12 are certainly in parallel
each of those combinations are part of a greater circuit, which alters depending on the switch position [open or closed]

Bottom right - certainly those 2 are in series.

 

[PeterO]

I think instead of doing the parallel first on the bottom, I think it would be correct to do it in series then parallel

Correct! [I misread your 24 as 2 so had to correct my answer]

EDIT: that analysis if for the switch in the open position.
The answer is quite different when the switch is closed