Question on Thevenin's Theorem

Discussion in 'Homework Help' started by mngeow, Nov 27, 2010.

  1. mngeow

    Thread Starter New Member

    Jan 28, 2010
    4
    0
    I have an exam coming up on circuit theory & analysis,there's this one question I can't seem to get right.

    [​IMG]

    The answers:

    [​IMG]

    Vab=Vth=V(8-j15)=V(6+j10) this is what I used to get my Vth.

    For Zth I used R(8-j15) // R(6+j10).

    What am I doing wrong?
     
    Last edited: Nov 27, 2010
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    It appears you are assuming points A and B have the same voltage.
     
  3. mngeow

    Thread Starter New Member

    Jan 28, 2010
    4
    0
    What do you mean?
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Warning - it's after bar hours for me... ;)
     
  5. mngeow

    Thread Starter New Member

    Jan 28, 2010
    4
    0
    Hmm,thats the only way I could think of to get Vab,since R(8-j15) // R(6+j10).
    What should the correct Vab be then?
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    You have 2 unknowns (A and B).

    You know the source voltage across both series circuits that source both A and B.

    Simultaneous equations or matrix solution is what I'm thinking.
     
  7. mngeow

    Thread Starter New Member

    Jan 28, 2010
    4
    0
    You can use simultaneous equations?!?!
    So far I've only learnt mesh analysis and the usual ohms law/kirchhoffs law so I'll have to get the answer using either one of those.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Solving the two equations is an algebraic step, not something that EE teaches, other than the required math courses for EE.
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
Loading...