- #1
[Circuits] Finding the Thevenin and Norton Equivalents #3
Click For Summary
Discussion Overview
The discussion revolves around finding the Thevenin and Norton equivalents in a circuit analysis context. Participants are addressing a specific issue related to obtaining a negative value for the Thevenin resistance (Rth) and the implications of current direction and voltage polarity in their calculations.
Discussion Character
- Homework-related
- Technical explanation
- Conceptual clarification
Main Points Raised
- One participant expresses confusion over obtaining a negative value for Rth and questions what went wrong in their calculations.
- Another participant suggests that the issue may relate to the direction of the current being injected into the circuit versus the polarity of the resulting voltage across the terminals.
- A participant speculates that their mistake might be due to the orientation of the 1A current source, questioning if it should have been pointing in the opposite direction.
- Another response clarifies that the orientation of the current source is not necessarily a mistake if the polarity of the voltage is correctly assigned, emphasizing the importance of understanding terminal designations when measuring voltage.
Areas of Agreement / Disagreement
Participants do not reach a consensus on the specific error leading to the negative Rth value. There are multiple viewpoints regarding the implications of current direction and voltage polarity, indicating that the discussion remains unresolved.
Contextual Notes
Participants reference the definitions of resistance and voltage measurement, but there are unresolved assumptions regarding the circuit configuration and the specific calculations performed.
- #2
gneill
Mentor
- 20,989
- 2,934
ainster31 said:
No doubt it has to do with the direction of the current that you're "injecting" into the circuit versus the polarity of the resulting voltage across the terminals. The resistance of a component (or circuit for that matter) is defined as the current into the port divided by the resulting potential across that port. The polarity of the voltage "measurement" is such that the terminal where the current is injected is taken to be positive:
Attachments
- #3
ainster31
- 158
- 1
So my mistake was that the 1A current source was pointing down when it should've been pointing up?
- #4
gneill
Mentor
- 20,989
- 2,934
ainster31 said:
Not a mistake per se, not if you take it into account when you assign the polarity of the voltage. You are looking for the potential at terminal a with respect to terminal b, so automatically that implies that the a terminal is the where you'd put the + lead of your meter (if you were measuring it). You are driving the current into the b terminal, so it becomes the "+" terminal for the resistance determination. That's contrary to the desired arrangement, and will result in a reversed sign for the voltage Vab.
Similar threads
- · Replies 1 ·
Engineering
Find the Thevenin equivalent circuit
- · Replies 42 ·
- · Replies 7 ·
- · Replies 12 ·
- · Replies 4 ·
- · Replies 10 ·
Engineering
How do I find Vth with the node voltage method?
- · Replies 10 ·
Engineering
Finding Current in a Thevenin Circuit
- · Replies 5 ·
- · Replies 15 ·
- · Replies 9 ·