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Can You Combine Current Sources Question

  1. May 21, 2013 #1
    http://imgur.com/09Rj0ND



    2. V=IR



    3. My real question is if I can combine the current sources. I'm pretty sure you cannot. I have combined the resistors in parallel, but I am not sure what to do next
     
    Last edited by a moderator: May 21, 2013
  2. jcsd
  3. May 21, 2013 #2

    berkeman

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    It depends on the situation, but in this case you cannot, IMO. There are current branches off of the top node, and the right side source is a dependent source.

    If you have two independent current sources in parallel, you would usually be able to combine them.
     
  4. May 21, 2013 #3

    SammyS

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    Display of your image.
    attachment.php?attachmentid=58919&stc=1&d=1369174508.png
     

    Attached Files:

  5. May 21, 2013 #4

    In order to solve this problem, am I correct in first combining the resistors? Then does Ib turn into 1Amp?
     
  6. May 21, 2013 #5

    berkeman

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    Not the way the circuit is drawn. Can you post the original circuit, so we can check that this drawing is correct?

    The way it is drawn is a bit confusing. You show a wire carrying a current Ib, but that wire shorts the top of the two resistors, so there is no wire segment that can carry a current...
     
  7. May 21, 2013 #6
    This is the original drawing, from my teacher
     
  8. May 21, 2013 #7

    berkeman

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    That's unfortunate.

    Well, you can still try to solve it, and hopefully it will yield the correct answer. Write KCL equations for the left node (to the left of the arrow "Ib") and for the right node, first assuming that they are at different voltages. Solve the right side equation to get a relationship between the voltage and the current Ib. Then assume that the two voltages are the same, and solve for the current Ib.

    Seems kind of clunky. I honestly do not know why you were given a circuit drawn like that...
     
  9. May 21, 2013 #8
    Thank you for the help!
     
  10. May 21, 2013 #9

    SammyS

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    Using Kirchhoff's Current Law:
    What is the current through the 2kΩ resistor? (in terms of Ib) ?

    What is the current through the 5kΩ resistor? (in terms of Ib) ?​
     
  11. May 21, 2013 #10
    2kΩ resistor 10Ib?

    5kΩ resistor 8Ib-1?
     
  12. May 21, 2013 #11

    SammyS

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    Yes.


    No.

    1 Ampere into the junction. Current of Ib out.

    Those together with current through 5kΩ , whichever direction you choose.
     
  13. May 21, 2013 #12
    I'm sorry, so the current through the 5kΩ is Ib-1?
     
  14. May 21, 2013 #13

    SammyS

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    Yes.

    Upward.
     
  15. May 21, 2013 #14
    Will solving for Vr1 by doing 5(Ib-1)=2(10Ib), solving for Ib, then plugging that backing to 5(Ib-1) work? seems too easy
     
  16. May 21, 2013 #15

    SammyS

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    Yes.

    It should be easy to check the results.
     
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