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Electric Circuits

  1. Oct 2, 2013 #1
    1. The problem statement, all variables and given/known data

    Hi. I have an electric circuit attached below. The question is to find the value Vg in order for the interconnection to be valid. The answer is -2V.
    My question is, why is the voltage minus?
     

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  2. jcsd
  3. Oct 2, 2013 #2

    Simon Bridge

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    You did the calculation - if you read the diagram correctly you set the [+] terminal to have a higher voltage than the [-] terminal. The minus sign means that the terminals are drawn the wrong way around.
    As to "why", you may have done the calculation wrong or maybe that's just the way the physics works out for that configuration.
     
  4. Oct 2, 2013 #3
    I doubt there is miscalculation, because the book had already given the answer key.
     
  5. Oct 2, 2013 #4

    gneill

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    Show how you would determine the potential of the controlled source on the left.
     
  6. Oct 2, 2013 #5
    ib=8A, Vx= ib/4 = 8/4=2V
     
    Last edited: Oct 2, 2013
  7. Oct 2, 2013 #6

    gneill

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    Check the defined direction of ib. Is the 8 A source really driving current in the direction indicated?
     
  8. Oct 2, 2013 #7
    Oh. You mean they are in opposite direction. So the current ib is negative, right?
     
  9. Oct 2, 2013 #8

    gneill

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    Right.
     
  10. Oct 2, 2013 #9
    Good. Thanks for the help.
     
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