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Potential -- Find the potential at node 3

  1. Aug 12, 2014 #1

    Rectifier

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    Gold Member

    The problem
    What is the potential at node 3, if the potential at node 1 is 0?

    XEOtcWF.jpg

    The attempt
    If I start at node 1 and move towards node 3
    1->2
    -5V
    2->3
    +(-3V)
    1->3
    -5+(-3)=-8V

    If I start at node 3 and move towards node 1
    3->2
    -(-3)
    2->1
    5
    3->1
    3+5=8V

    I am not really sure what is right here.
     
  2. jcsd
  3. Aug 12, 2014 #2

    berkeman

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    Staff: Mentor

    The problem looks overconstrained and inconsistent. Where is it from?

    And when you go in the direction of - to +, that is an increase in potential. I get 2 different answers for going the 2 different ways from node 1 to node 3...
     
  4. Aug 12, 2014 #3
    KVL in the loop, starting at 3..
    3->2
    -3v(rise)
    2->1
    -5v(fall)
    1->4
    -9v(fall)
    4->3
    17V(rise)
    -3-5-9+17=0, so the voltage in the loop adds up.

    Now from V3->V2->V1
    V3-3-5=0
    V3=8V
    Now from V3->V4->V1
    V3-17+9=0
    V3=8V

    Seems okay to me?
     
  5. Aug 12, 2014 #4

    berkeman

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    Staff: Mentor

    Ah, I see what fooled me. They labeled the right-hand voltage as negative, instead of relying on the +/- signs to determine the direction of the voltage. That's very non-standard in electronics, but I guess I should have seen that trick part of the question. Thanks for clearing that up! :smile:
     
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