Source Transformations: Find Vth & Rth

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Discussion Overview

The discussion focuses on finding the Thevenin equivalent circuit using source transformations. Participants are attempting to determine the Thevenin voltage (Vth) and Thevenin resistance (Rth) while navigating the legality of their transformations and the correctness of their steps.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • Some participants express uncertainty about the legality of their source transformation steps, particularly in finding Vth.
  • One participant claims to have correctly determined Rth but questions the correctness of their method for finding Vth.
  • Another participant points out an error in the transformation of a voltage source to a current source, emphasizing that the associated resistor must be in parallel with the current source.
  • There is a suggestion to work from one end of the circuit to the other in stages, converting between source types as necessary to simplify the circuit.
  • Participants discuss the potential to "swallow up" resistors through transformations to simplify the analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the transformations. Multiple competing views on the steps and legality of the transformations remain, and the discussion is unresolved regarding the correct approach to finding Vth.

Contextual Notes

Participants have not fully resolved the assumptions regarding the circuit configurations and the specific steps taken in their transformations. There are indications of missing details in the transformations that could affect the outcomes.

jdawg
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Homework Statement


Find the thevenin equivalent circuit by performing source transformations only.

Homework Equations

The Attempt at a Solution


Answers: Vth=60v and Rth=30.
I managed to get Rth correct, but I'm not sure if everything I did was "legal". I can't seem to find Vth.
 

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jdawg said:

Homework Statement


Find the thevenin equivalent circuit by performing source transformations only.

Homework Equations

The Attempt at a Solution


Answers: Vth=60v and Rth=30.
I managed to get Rth correct, but I'm not sure if everything I did was "legal". I can't seem to find Vth.
In the 3rd circuit, your transformation of V into I is wrong since the resistor and current source(transformed) are not in parallel. But you don't need a 3rd step. I think in the 2nd circuit itself, the answer is obvious (60V).
 
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Your third step is incorrect. When a voltage source is transformed into a current source the associated resistor must end up in parallel with the current source. Also, you should work from one end of the circuit to the other, towards the output, in stages.

Your first step, converting the 4 A source to a 40 V source allowed you to "swallow up" one 10 Ω resistor. The logical next step would be to convert this "new" voltage source and resistance back to a current source allowing you to "swallow up" more of the circuit with simple parallel or series combinations. Don't be afraid to convert back and forth between source types if it allows you to make progress in reducing the circuit.
Fig1.png
 
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Thanks, I'll try reworking it!
 

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