[Circuits] Computing the Thevenin Equivalent #2

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Discussion Overview

The discussion revolves around determining the equivalent resistance in a circuit as part of a homework problem related to Thevenin equivalents. Participants explore the configuration of resistors in relation to independent sources and node positions.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the two resistors are in series after turning off independent sources, based on the absence of other elements.
  • Another participant proposes moving the 60 Ohm resistor to analyze the configuration with respect to specific probe points, questioning whether the resistors are in series or parallel.
  • Some participants assert that the resistors appear to be in parallel, while also noting that they can be perceived as in series depending on the position of the 60 Ohm resistor.
  • A participant emphasizes that the position of the nodes is crucial to determining the configuration, stating that the resistors are indeed in parallel.
  • There is a side discussion about the implications of removing the load and how that affects the classification of the resistors as series or parallel.
  • One participant notes that the classification depends on the context and specifies that if only the two resistors are considered, they are in series, resulting in a total resistance of 90 Ohms.

Areas of Agreement / Disagreement

Participants express differing views on whether the resistors are in series or parallel, depending on the configuration and context provided by the node positions. No consensus is reached on a definitive classification.

Contextual Notes

Participants highlight the importance of node positions and the context in which series or parallel classifications are made, indicating that assumptions about connections can lead to different interpretations.

ainster31
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Homework Statement



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Homework Equations


The Attempt at a Solution



I am trying to find the equivalent resistance for part b.

First, we turn off independent sources. We open circuit the 2A source and we close circuit the 30V source. We're left with two resistors. Are they in series or parallel and why? I think it is in series because there's no other elements other than the two resistors.
 
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Slide the 60 Ohm resistor down and to the right, into the position where the 30V source used to be. Now do the resistors look like they are in series or parallel, with respect to the two probe ponts 1 & 2?
 
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berkeman said:
Slide the 60 Ohm resistor down and to the right, into the position where the 30V source used to be. Now do the resistors look like they are in series or parallel, with respect to the two probe ponts 1 & 2?

They look like they're in parallel but I can also make them look like they're in series by sliding the 60 ohm resistor even further past the (2) node.
 
ainster31 said:
They look like they're in parallel but I can also make them look like they're in series by sliding the 60 ohm resistor even further past the (2) node.

But then you've changed the question. The position of the 1 & 2 nodes is given to be where they are with respect to the two resistors. They are indeed in parallel. :smile:
 
berkeman said:
But then you've changed the question. The position of the 1 & 2 nodes is given to be where they are with respect to the two resistors. They are indeed in parallel. :smile:

But I removed the load so (1) and (2) aren't connected to anything.

As a side-question, what if we ignore (1) and (2), would the resistors be in series or parallel?
 
ainster31 said:
But I removed the load so (1) and (2) aren't connected to anything.
I don't understand what that means.

As a side-question, what if we ignore (1) and (2), would the resistors be in series or parallel?

It all depends. You have to specifiy in series or parallel with respect to what. That circuit reduces to just the two resistors connected nose-to-tail by wires. If that's all there is, they are in series to make a total of 90 Ohms going around the loop.
 
I think I get it. Thanks.
 

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