Equivalent Capacitance Between Points a and b for Group of Capacitors

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Homework Help Overview

The discussion revolves around finding the equivalent capacitance between two points in a circuit containing multiple capacitors. Participants are examining the configuration of capacitors and how they relate to each other in terms of series and parallel connections.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to visualize the circuit by combining capacitors and questioning the arrangement of capacitors after simplification. There are discussions about labeling capacitors for clarity and identifying whether certain capacitors are in series or parallel based on their connections.

Discussion Status

The discussion is ongoing, with participants providing diagrams and asking for clarification on the arrangement of capacitors. Some guidance has been offered regarding the identification of series and parallel configurations, but no consensus has been reached on the specific setup of the capacitors in the original circuit.

Contextual Notes

Participants are navigating the complexity of the circuit layout and the implications of current flow on capacitor arrangement. There are mentions of assumptions that may affect understanding, and the need for clearer labeling in diagrams has been highlighted.

AznBoi
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Homework Statement


Find the equivalent capacitance between points a and b for the group of capcitors connected as shown below.

http://img250.imageshack.us/img250/7816/40ha4.th.png


Homework Equations


Series/Parallel combinations.


The Attempt at a Solution



I don't get how the two parallel capacitors, after being combined, are positioned in the circuit. Here's my attempt after combining a few capcitors.

http://img250.imageshack.us/img250/4610/401gx0.th.png
 
Last edited by a moderator:
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I'm not sure I can follow your second diagram correctly without making a few assumptions (which may be wrong). Perhaps you can give each cap in the original circuit a label and label your attempt according to the original circuit.
 
ranger said:
I'm not sure I can follow your second diagram correctly without making a few assumptions (which may be wrong). Perhaps you can give each cap in the original circuit a label and label your attempt according to the original circuit.

Yeah, I should have labled them. I just reduced the 3 parallel capacitors. I'm mostly unsure of where the 2 upper parallel capacitors will be set up. Will it just be a line like my attempt?
 
AznBoi said:
Yeah, I should have labled them. I just reduced the 3 parallel capacitors. I'm mostly unsure of where the 2 upper parallel capacitors will be set up. Will it just be a line like my attempt?

What 3 parallel capacitors?

The upper part of the original circuit has more that two caps in parallel.
 
ranger said:
What 3 parallel capacitors?

The upper part of the original circuit has more that two caps in parallel.

Sorry about that. Here is my whole attempt. I circled the capacitors that I combined and the black arrow is the result. I have a question. Are the capacitors that I pointed to all parallel? How do you tell the difference between parallel and series capacitors? They all seem to be on the same wire.. thanks.

http://img201.imageshack.us/img201/198/40kd8.th.png
 
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To simplify the case of whether components are in series or parallel (dont worry, what's applies here works for caps also). Think of them as being resistors. Consider this diagram (ignore the formulas):
http://upload.wikimedia.org/wikipedia/en/4/47/Cdr.GIF
You see a current, IT, entering the two resistor branch. Now are these two resistors in parallel or series? Why?
Knowing this, you will be able to answer the question you circled.
 
Last edited by a moderator:
ranger said:
To simplify the case of whether components are in series or parallel (dont worry, what's applies here works for caps also). Think of them as being resistors. Consider this diagram (ignore the formulas):
http://upload.wikimedia.org/wikipedia/en/4/47/Cdr.GIF
You see a current, IT, entering the two resistor branch. Now are these two resistors in parallel or series? Why?
Knowing this, you will be able to answer the question you circled.

Well from your provided diagram, it's pretty obvious that it is parallel because the total current is branched out into 2 separate onces and then coming back together. However, in this problem, the capacitors are like: [l] and it seems like they are in series because they don't exactly branch out, it is the same wire.. So are the capacitors that I circled for the first step in series? the ones on: [ and ]
 
Last edited by a moderator:
Well taking the original diagram (upper left), the two caps are not in parallel. Let's say we trace a current coming from the node a. The current splits into three parts. One going left, down, and right. The current that flows left flows through two caps, so these two now have the same current flowing through them. The one that flows down flows into one cap, the one that flow right flows into two caps, so these two now have the same current flowing through them. All three currents then rejoin at the base of these 5 caps and flow into the second set...

So we have Ileft[tex]\not=[/tex]Idown[tex]\not=[/tex]Iright, therefore these three bracnches must be in...? How about two caps each in the upper left and right branch? So we have to consider two things, whether the branches are in series/parallel and whether the caps on the individual branches are series/parallel. Just tracing a current should be enough to figure this out.
 
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