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Direction of current in the figure?

  1. Apr 19, 2013 #1
    Direction of current in the figure??

    1. The problem statement, all variables and given/known data

    What must the emf in the figure be in order for the current through the 7.00-ohm resistor to be 1.76A? Each emf source has negligible internal resistance. Figure

    http://i239.photobucket.com/albums/ff92/anakris_24/yf_Figure_26_51.jpg

    2. Relevant equations

    Kirrchoff's Laws

    3. The attempt at a solution

    I know well how to use the laws but my problem here is in determining the direction of current through the 7Ω resistor. Is it up or down and why? ... In the manual it say it goes down due to polarity of the battery.. But it can actually go out of battery 1(left) and battery two?
     
  2. jcsd
  3. Apr 19, 2013 #2

    gneill

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    Staff: Mentor

    Try applying superposition. What direction does the current flow through the 7 Ω resistor due to each source when taken individually?
     
  4. Apr 19, 2013 #3

    CWatters

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    Science Advisor
    Homework Helper

    I don't understand your explanation. Even if the current flows out of the 24V battery into the ε battery the top end of the 7R will still be +ve wrt the bottom end.

    If ε is +ve then I can't see how the current can ever flow upwards through the 7R.

    Edit: It would be bad practice to show ε as -ve with the battery drawn that way around. It would be ok to show a voltage source with the arrow pointing upwards and ε marked as -ve but that's not what you have here.
     
  5. Apr 19, 2013 #4

    CWatters

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    How about solving it twice. Once assuming the current flow down through the 7R and one assuming it flow up through the 7R. What do you get?
     
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