How Do You Approach an Irregularly Shaped DC Circuit Problem?

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Homework Help Overview

The discussion revolves around an irregularly shaped DC circuit problem involving multiple resistors and their equivalent resistances. Participants are attempting to understand how to approach the problem and clarify the relationships between the resistors based on the provided circuit diagram.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants express confusion about how to set up the equations for the circuit, with some attempting to derive relationships between resistors based on their interpretations of the circuit layout. Questions arise regarding the correct application of series and parallel resistor combinations.

Discussion Status

The discussion is ongoing, with participants sharing their interpretations and calculations. Some have identified potential errors in their approaches, while others are questioning the assumptions made about the circuit's configuration. There is no explicit consensus yet, but participants are engaging in clarifying the problem's requirements.

Contextual Notes

Some participants reference the Y-delta transform, suggesting that the problem may involve deriving transformations that are relevant to their coursework. There is also mention of the circuit not being symmetrical, which influences the equations formed.

Elbobo
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Homework Statement


http://img144.imageshack.us/img144/9724/tricircuitxv4.jpg
http://g.imageshack.us/img144/tricircuitxv4.jpg/1/


Homework Equations



Re = R1 + R2 + R3

The Attempt at a Solution



I don't really understand this problem. I'm not sure how to approach it. I thought 5 = Rb + Rc, and I did that for all the rest of the resistors to solve the system but that was wrong.

Can someone just help me understand what the problem is asking and what it gives?
 
Last edited by a moderator:
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I would interpret it to mean that

Ra + Rb = 6

etc.

3 equations - 3 unknowns
 
That's exactly what I did, and got a nice rational number - 3.5 (the answer is almost never rational). It's wrong.
 
Elbobo said:
That's exactly what I did, and got a nice rational number - 3.5 (the answer is almost never rational). It's wrong.

I see what's wrong.

Ra + Rb = 6 || (5 + 6)

The equivalent resistance from one to the other includes the alternate series pair in parallel with the direct one.
 
So you're saying Ra + Rb = (1/6 + 1/11)^-1?

Isn't that saying the total resistance of the first circuit equals only the sum of the resistances Ra and Rb?
 
Elbobo said:
So you're saying Ra + Rb = (1/6 + 1/11)^-1?

Isn't that saying the total resistance of the first circuit equals only the sum of the resistances Ra and Rb?

Yes that's the calculation.

No, it's how the resistors are taken. Note the circuit is not symmetrical. You get pair-wise different equations.

There's 6 || 11 and 6 || 11 and 5 || 12
 
Ah ok, thank you.
 
Elbobo said:

Homework Statement


http://img144.imageshack.us/img144/9724/tricircuitxv4.jpg
http://g.imageshack.us/img144/tricircuitxv4.jpg/1/


Homework Equations



Re = R1 + R2 + R3

The Attempt at a Solution



I don't really understand this problem. I'm not sure how to approach it. I thought 5 = Rb + Rc, and I did that for all the rest of the resistors to solve the system but that was wrong.

Can someone just help me understand what the problem is asking and what it gives?

This is known as the Y-delta transform (though this question is probably to get you guys to derive the transformation to be covered in class!):
http://en.wikipedia.org/wiki/Y-Δ_transform
 
Last edited by a moderator:

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