Source transformation, find the error

  • #1

Homework Statement


[PLAIN]http://img5.imageshack.us/img5/2959/question2e.jpg [Broken]


Homework Equations


- A current source in parallel with a resistor can be transformed into a voltage source in series with a resistor. R stays the same and Vs = R*Is



The Attempt at a Solution


I have tried it in two ways. Both ways give me different results.

The first way is to transform the two voltage sources into current sources, and do the obvious simplifications to obtain a current source in parallel with a resistor. Then transform that into voltage source with resistor in series: 22.85 volts voltage source with 5.714 ohm resistance in series.

The second way, which is the one I think is wrong, starts like this. Transform the current source in parallel with 10 ohms resistor into a voltage source with 10 ohms resistor. Transform the initial voltage sources into current sources:
[PLAIN]http://img822.imageshack.us/img822/3395/sourcetransfomration2.jpg [Broken]

Why isn't it giving the same result?? To me, every step look perfectly valid.. Surely there is something I don't understand about source transformation.
Thank you
 
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Answers and Replies

  • #2
gneill
Mentor
20,925
2,867
In your second method you've "lost track" of the nodes where output voltage and equivalent resistance are to appear.

attachment.php?attachmentid=40059&stc=1&d=1318767025.gif
 

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