Help with this simple nodal analysis issue, please

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Homework Help Overview

The discussion revolves around a nodal analysis problem related to a circuit diagram, specifically focusing on the voltage across a resistor (R3) and the application of Kirchhoff's Voltage Law (KVL). The original poster is attempting to reconcile their calculations with those presented in a textbook.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster is questioning the validity of their calculated voltage across R3 compared to the textbook's value. They express confusion regarding the application of KVL as mentioned in the book. Another participant suggests converting current sources to voltage sources to simplify the analysis.

Discussion Status

Some participants are exploring different methods to approach the problem, with one suggesting a conversion technique that could clarify the situation. The original poster acknowledges the assistance but has not yet confirmed their understanding or resolution of the issue.

Contextual Notes

The original poster has provided circuit diagrams and values for voltages (V1 and V2) but is struggling with the interpretation of the textbook's instructions and the calculations for R3. There is a noted discrepancy between their findings and the textbook's answer.

PainterGuy
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Hi, :)

1: http://img19.imageshack.us/img19/2256/nodaldiagram1.jpg (diagram of circuit and few other details)
2: http://img36.imageshack.us/img36/5405/nodaldiagram2.jpg (solution)

The book asks "Find the magnitude and polarity of the voltage across each resistor".

I was trying to find the magnitude and polarity across R3 in the circuit diagram (please have a look on the link #1).

The values for V1 and V2 are correct. V1 is -14.9v, and V2 is -12.7v. The magnitude for voltage across R3 I found was 14.8v, but the book says it's 9.71v.

I4 is -3.7A (the assumed direction by me was from left to right of screen as is shown in the scan).

The book also says: V_R3 = V1 + 12 -V2. I don't get this step. Is the book applying KVL here, then how. Please help me with this. Many thanks for the help.

Cheers
 
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You may find it simpler to convert both current sources (and their parallel resistances) to voltage sources (i.e., convert Norton to Thevenin). Then you'll have a single loop with only resistances and voltage sources. Easy peasy.

By the way, using this method I see that the voltage across R3 is indeed 9.71V as your book indicates.
 
gneill: Many thanks for the reply. Sorry I wasn't able to says thanks in timely manner. As a matter of fact, I have been busy with some stuff lately. I appreciate your help.

Cheers
 
PainterGuy said:
gneill: Many thanks for the reply. Sorry I wasn't able to says thanks in timely manner. As a matter of fact, I have been busy with some stuff lately. I appreciate your help.

Cheers

No worries. Glad to help.
 

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