Source Transformation Confusion

Discussion in 'Homework Help' started by EE_Bob, Jul 31, 2009.

  1. EE_Bob

    Thread Starter Member

    Jul 21, 2009
    16
    0
    This problem comes from Fundamental of Electric Circuits 3/4e text.
    Find Vo using source transformation.
    [​IMG]

    The first source transformation is the 3 amp current source in parallel with the 4 ohm resistor.

    The book lists this circuit as the correct transformation
    [​IMG]

    This is how I would incorporate the transformation.
    [​IMG]

    Why is my transformation incorrect?
     
  2. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    EE_Bob,

    Do you realize how many books have that exact name? If you want to identify the book, you need to give more details than that. Such as author, publishing date, publisher, etc.

    What makes you think it is? Putting the 4k resistor on one side the voltage source or the other is not going to change the loop current or the voltage around the loop. Not in a series curcuit.

    Ratch
     
  3. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    Ratch is correct that your transformation is not wrong. The main issue with your chosen step is that it does not move you in the direction of greater simplicity, which should be your goal here.

    Just combine the 4 ohm and 2 ohm resistor into one 6 ohm resistor and you will have a simpler circuit. Then decide what additional transforms bring you to a simple problem. Ultimately you want one source, one source resistance and one load resistance with voltage Vo. Then the problem of calculating Vo is easily solved
     
  4. EE_Bob

    Thread Starter Member

    Jul 21, 2009
    16
    0
    Thank you for the quick replies. I was going crazy over that.

    @Ratch, The text is the 4th edition of "Fundamentals of Electric Circuits" by Charles Alexander and Matthew Sadiku copyright 2009.

    Pretty much all of my questions will be from this one text.
    Thx again, till next time,
    -Bob
     
  5. Waffles

    New Member

    Oct 21, 2009
    2
    0
    I hate to bump an old thread but I was wondering why he can switch positions of the 12V and 4 ohm resistor. What makes this valid.
     
  6. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    Waffles,

    In a series circuit, what would be the difference in current when the resistor is on the north or south side of the 12V source? Series current calculations don't care about the positions of the series elements.

    Ratch
     
  7. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,286
    331
    He didn't switch them. The 12V you see on the left after transformation came from converting the 3 amp current source in parallel with 4Ω into a 12 volt voltage source in series with a 4 Ω resistor. This 12V source didn't come from the right side.

    On the right, the 12 volt source in series with 3Ω was transformed into a 4 amp source in parallel with 3Ω. That is, the right side 4 amp source after transformation isn't the 4 amp source that was on the left.
     
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