Help with this simple nodal analysis issue, please

AI Thread Summary
The discussion revolves around a nodal analysis issue in a circuit diagram, specifically focusing on the voltage across resistor R3. The user correctly calculated V1 and V2 but found a discrepancy in the voltage across R3, obtaining 14.8V while the book states it should be 9.71V. A suggestion was made to convert current sources to voltage sources for simplification, which confirmed the book's value of 9.71V for R3. The user expressed gratitude for the assistance received in clarifying the analysis. The conversation highlights the importance of understanding circuit analysis techniques for accurate voltage calculations.
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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