Thevenin's theorem

Discussion in 'Homework Help' started by Aoron, Dec 5, 2010.

  1. Aoron

    Thread Starter Member

    Aug 5, 2010
    10
    1
    I know how to implement the method and so on, but i can't make any sense of it. The two ways we find out R(th) and V(th) seem to contradict each other. We find R(th) by looking at the whole resistance of the circuit from R(L) perspective, but the way we find V(th) sounds to me like finding the voltage of the LOOP in which R(L) is in, and not from R(L) perspective. I assumed that V(th) should be more like the voltage drop across the very R(L) resistor itself not the loop in which it is located. I spent much time trying to understand the logic behind the theorem but i need help.

    Appreciate your attention.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    It would be helpful if you could post a sample of a Thevenin Problem that you have encountered. That will give you and our members a point of discussion so that this thread can be more effect to you and others that may have similar questions.

    Remember, if you are confused there are others who share your confusion.

    hgmjr
     
  3. mik3

    Senior Member

    Feb 4, 2008
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  4. Aoron

    Thread Starter Member

    Aug 5, 2010
    10
    1

    I am considering the theorem in general so there isn't really a particular problem. please read my first post in this thread as it describes my issue in details.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    It would still be helpful if you could find a specific problem that would permit a more detailed discussion of the specifics of your question about the Thevenin Method.

    hgmjr
     
    Last edited: Dec 5, 2010
    Aoron likes this.
  6. mik3

    Senior Member

    Feb 4, 2008
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    The Thevenin voltage is the voltage across the two points of interest without the load resistor in the circuit. Use any method you want to calculate that voltage.
     
  7. blah2222

    Well-Known Member

    May 3, 2010
    554
    33
    In short, you are basically simplifying the desired circuit connected to a certain load into a voltage and resistor in series. This essentially is all that the load sees. Though it might seem from the diagrams that V(Th) is the voltage around R(L), it is not. V(Th) is the open circuit voltage that would be seen before the load was connected (open circuit). R(Th) is the value that encompasses the entire resistivity of the circuit before R(L) is set in place.

    With V(Th) and R(Th), the whole functionality of the circuit between the nodes around R(L) can be shown in the simplified series form.

    Hope that helped.
     
    Aoron likes this.
  8. Aoron

    Thread Starter Member

    Aug 5, 2010
    10
    1
    |--R2---|----R3--|
    | **** |****** |
    | *****R1**** R(L)
    O V ***|****** |
    | *****|****** |
    |______|________|

    |--R2---|--------|
    | **** |****** |
    | *****R1**** R(L)
    O V ***|****** |
    | *****|****** |
    |______|________|


    lines & dashes represent wires
    asterisks represent space so nvm them
    O represents voltage source
    R(L) = resistor load

    "blah2222" adressed the type of confusion am facing in making a correct intuitive sense of the theorem. V(th) is said to be the voltage "seen" by R(L) while R(th) is the resistance "seen" by R(L). However, i still can't understand V(th). if some one could follow on from blah2222's "Though it might seem from the diagrams that V(Th) is the voltage around R(L), it is not. V(Th) is the open circuit voltage that would be seen before the load was connected (open circuit). R(Th) is the value that encompasses the entire resistivity of the circuit before R(L) is set in place." i would be grateful.

    Thanks your kind attention
     
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