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Node voltage analysis problem

  1. Sep 8, 2005 #1
    The question asks me to find [tex]i_o[/tex] and [tex]V_o[/tex]

    I'm not sure how to do it since I dont know which way the current goes on the 8 ohms resistor. any ideas?
     

    Attached Files:

  2. jcsd
  3. Sep 8, 2005 #2

    ranger

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    Current enters from the negative side and exits from the positives. Current always flows from the negative side of the battery (electron convention).

    I wish I could help you more, but I cant see the posted image.
     
  4. Sep 8, 2005 #3
    that's not really true because my book has examples that have current going into the positive side. All that does is switch the voltage from negative to positive, or vise versa,
     
  5. Sep 8, 2005 #4

    BobG

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    The attachment is still awaiting approval. Depending on how complicated the circuit is, you don't know what direction the current is going until you solve the circuit. You pick a direction to set up your equation (and make sure to label you circuit so you remember which direction you picked). If you picked right, the current will be positive. If you picked wrong, the current will be negative.

    You didn't explain what you're trying to do, so without seeing the attachment, it's hard to give a good answer. In general, for node voltage analysis, you can set all the currents as leaving the node (obviously at least one has to be going into the node, but that illustrates just how insignificant the initial direction you pick is). If using mesh current, just set all the currents to go either clockwise or counter-clockwise - doesn't matter which, but things are generally easier to keep straight if all the directions are the same.
     
  6. Sep 8, 2005 #5
    okay, the image is up, any ideas oh how to find I and v?
     
  7. Sep 8, 2005 #6

    BobG

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    Node voltage analysis. Put your ground on the bottom and you only have one node to solve for (Node A). Set all your currents coming out of the top node (this means the current source is giving you -6 Amps).

    You need to make a substitution for Io in the dependent source. If you know ohm's law, you should be able to figure out what to substitute in place of Io.

    Setting up your equation is the hard part. If you set it up right, you only have one variable to solve for. You have a parallel circuit, so vo is easy once you figure out the voltage at Node A.
     
  8. Sep 8, 2005 #7
    ah! okay, forgot that voltage was constant in a parallel circut. I just set the current to add up to 6A and solve for voltage...

    V/2+V/8+V/8=6

    so V=8
    thanks
     
  9. Sep 8, 2005 #8

    ranger

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    Current is the flow of electrons through a conductor. And as we know electrons have a negative(-) charge. This would make perfect sense to have the electrons start off from the negative terminal of the power source and end up at the positive ternimal. So I really cant understand why some books have current flowing from the positive ternimal. That isnt really happening right? I know that we have two conventions used. I too was taught using the conventional method, but I really perfere the electron convention. But I still fail to see why we have two. Anyone care to explain?
     
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