What happens to the node after a source transformation?

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Discussion Overview

The discussion revolves around the effects of source transformation in electrical circuits, specifically focusing on the behavior of currents at nodes before and after the transformation. Participants explore concepts related to current division, the impact of resistances, and the verification of source transformation correctness.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether the current entering node 5 before the transformation should equal the current entering node 4 after the transformation, suggesting a value of 34.50 mA.
  • Another participant asserts that the currents are not equal due to the presence of multiple paths for current division at node 5 before transformation, and explains how the transformation affects the current supplied by the voltage source.
  • A participant asks if the two resistors (4 ohm and 2 ohm) can be added together, indicating a potential misunderstanding of their configuration.
  • Responses clarify that the resistors are not in series, which affects how they can be combined in calculations.
  • One participant acknowledges that the current entering the main circuit remains the same before and after the transformation, but emphasizes the importance of including the resistance in the analysis.
  • Another participant suggests a method to verify the transformation by comparing currents entering unchanged circuit elements and recommends visualizing the source with its impedance.

Areas of Agreement / Disagreement

Participants express differing views on the equality of currents at the nodes before and after the transformation, with some asserting that they should be equal while others argue that the presence of resistances alters this relationship. The discussion remains unresolved regarding the exact implications of the source transformation on current values.

Contextual Notes

There are limitations in the discussion regarding assumptions about circuit configurations and the specific roles of resistances in the source transformation process. The mathematical steps involved in verifying the transformation are not fully resolved.

garr6120
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I have one circuit and another with a source transformation figure a and b respectively. My question after transforming the 30 mA source shouldn't the current going into node 5 equal the current going into node 4?

Screen Shot 2017-10-12 at 12.27.36 AM.png

Figura a. Before the transformation of the source

Screen Shot 2017-10-12 at 12.27.14 AM.png

Figure b. After the source transformation.

To clarify my question shouldn't the current going into the node before the transformation (34.50 mA) equal the the current going into the node after the transformation so again 34.50 mA)? If the two current's aren't supposed to be equal explain what concept I am missing about source transformation and how I can check if the source transformation is correct?
 
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garr6120 said:
To clarify my question shouldn't the current going into the node before the transformation (34.50 mA) equal the the current going into the node after the transformation so again 34.50 mA)?
No.
Before source transformation, there are four paths for current division at node 5. During source transformation, one of them (resistance in parallel with the current source) gets shifted in series with the voltage source. So, current supplied by the voltage source= current supplied by current source-current through the parallel resistance (which is now shifted).
Hence,
Current supplied by the voltage source=
30mA-19.5mA=10.5mA.
 
cnh1995 said:
No.
Before source transformation, there are four paths for current division at node 5. During source transformation, one of them (resistance in parallel with the current source) gets shifted in series with the voltage source. So, current supplied by the voltage source= current supplied by current source-current through the parallel resistance (which is now shifted).
Hence,
Current supplied by the voltage source=
30mA-19.5mA=10.5mA.
Can I add the two resistors the 4 ohm and 2 ohm?
 
garr6120 said:
Can I add the two resistors the 4 ohm and 2 ohm?
No.
 
cnh1995 said:
No.
That’s because of the node right?
 
garr6120 said:
That’s because of the node right?
Yes, they are not in series.
 
Just to point something out... garr6120 you are partially right. The current going into the main circuit should and will be the same before and after the source transformation. But you forgot that the 2k resistor is part of the source the way you presented the problem. The current going out from your old and new source should equal each other, but you need to include the resistance.

30-19.5=10.5
 
You can check your work by comparing the current entering the unchanged circuit elements. if you have difficulty, draw a dotted line around your source, including the source impedance. the IO should be the same
 

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