Nodal Analysis 1 equation 2 Unknowns Problem

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Discussion Overview

The discussion revolves around a nodal analysis problem involving one equation with two unknowns in an electrical circuit. Participants are examining the application of Kirchhoff's Current Law (KCL) and the formulation of equations based on circuit components and their relationships.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about their KCL formulation, leading to a conclusion of 0=0, and questions whether voltage sources can be treated as a supernode.
  • Another participant challenges the conclusion of 0=0, suggesting that the algebra does not support this outcome.
  • A different participant points out that the initial expression lacks an equal sign, questioning whether currents are being summed correctly at each node.
  • There is a correction proposed regarding the KCL equation, indicating that the original formulation was incorrect and providing an alternative expression.
  • One participant derives a new equation from the corrected KCL, showing that it leads to a non-trivial result, contradicting the earlier conclusion of 0=0.
  • Another participant acknowledges the correction and suggests that a second equation can be obtained from another branch in the circuit.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are competing views on the correctness of the KCL formulation and the resulting equations. The discussion remains unresolved regarding the proper application of nodal analysis in this context.

Contextual Notes

There are limitations in the discussion, including potential missing assumptions in the KCL formulation and the dependence on how nodes and branches are defined in the circuit analysis.

eatsleep
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http://imgur.com/W9sWTv7V=IR, that is all I think
3. I have put my ground at the bottom branch. I have tried to write a KCL for the top branch but end up with 0=0 when I substitute in equivalencies. My KCL: (V1+5Ix-0)/20+2+Ix=0. (V1+5Ix)/20=-2-Ix. So 0=0. I am not sure if I am writing my KCL correct also I know I am missing something.

Can I make the voltages sources and the top node for a supernode?
 
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I think you are being hasty in concluding that you first equation develops into 0 = 0. The algebra doesn't support this conclusion.
 
Your first expression isn't even an equation - where's the = sign?

It says to use nodal analysis. Are you summing currents to zero at each independent node?

(I myself don't ever use KCL. I sum currents at each node to zero - is that KVL? I don't know. Never heard of a supernode either).
 
SteamKing said:
I think you are being hasty in concluding that you first equation develops into 0 = 0. The algebra doesn't support this conclusion.

Is it correct that (V1+5Ix)/20=-2-Ix ? If so that is where 0=0 comes from
 
If (V1 + 5Ix)/20 = -2 - Ix,
then
(V1 + 5Ix) = 20*(-2 - Ix)
(V1 + 5Ix) = -40 - 20Ix
V1 + 25Ix = -40

which is not 0 = 0
 
eatsleep said:
My KCL: (V1+5Ix-0)/20+2+Ix=0. (V1+5Ix)/20=-2-Ix.

This is wrong. It should be:

(V1-5Ix-0)/20+2+Ix=0
 
With the Electrician's correction, you have one equation. Your second equation comes from the branch on the right side, giving its own equation relating V1 and IX.
 

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