a question on norton method..

Discussion in 'Homework Help' started by transgalactic, May 15, 2008.

  1. transgalactic

    Thread Starter Active Member

    Apr 29, 2008
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    0
    http://img391.imageshack.us/my.php?image=img8855ew6.jpg

    why "I" is negative??
    i know that KCL says that the sum of the currents that goes in
    equals the sum of the currents that goes out

    here i dont know what current goes into the node
    and what current goes out??
    i dont know how you decided the direction of each current

    i am new to this stuff
    and i think that the "I" current is pointed up
    so it goes into the node
    the second current the goes threw "R1" also come into the node
    because the currect goes from the plus of the battery to minus of the battery

    where did i go wrong??

    i cant see the conventions here

    i cant see how the currents flow using these conventions

    in what case we have e-v and in what v-e
    ???
     
  2. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    You pick the direction of the currents. If you pick backwards from actual current flow, the answer will come out negative. It will be correct.

    In this case, you are saying that all of the currents are going out. Since none are going in (because you said), the other side is 0.

    \frac{e - V}{R_{1} is the current going out through R1.
    \frac{e}{R_{1} is the current going out through R2.
    And since you are talking about currents going out, you must use -I

    You could just put it on the other side of the equation and it would be positive. But through simple algebra you can see that they are the same.
     
  3. Caveman

    Active Member

    Apr 15, 2008
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    0
  4. transgalactic

    Thread Starter Active Member

    Apr 29, 2008
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    but this is normal KVL equation

    why it called the norton method???
     
  5. Caveman

    Active Member

    Apr 15, 2008
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    0
    It is not called the norton method. That was my point. And it doesn't really use KVL. It primarily uses KCL at the various nodes to provide a methodical process for solving these kinds of circuits.
     
  6. transgalactic

    Thread Starter Active Member

    Apr 29, 2008
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    0
    this example is for using norton method on a circuit

    where does the norton stuff come out??
     
    Last edited: May 15, 2008
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  8. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    The premise of Norton Theorem is that you can reduce (simplify) a linear circuit to a single current source and parallel resistance (the Norton Equivalent Circuit) driving a load.

    See: http://www.allaboutcircuits.com/vol_1/chpt_10/9.html

    Also see the related Thevenin Theorem: http://www.allaboutcircuits.com/vol_1/chpt_10/8.html

    And finally the Norton-Thevenin Equivalences: http://www.allaboutcircuits.com/vol_1/chpt_10/10.html

    Dave
     
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