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Kirchhoff's laws question circuit?

  1. Apr 25, 2013 #1
    1. The problem statement, all variables and given/known data

    I have the circuit in the figure.I have to find i1 and R

    2. Relevant equations

    I am thinking about applying the division of the current and any of the K's laws but I dont know where to start.Can you pleas give me a hint?

    3. The attempt at a solution
    I tried to find the voltage in the 4 Ohm resistance and it is 8 Volt.Since 4 oHm is in parallel with 8 Ohm ,then their voltage equals.This is how far I have got.
    http://i.imgur.com/FoQmlFl.jpg?1?3770
     
  2. jcsd
  3. Apr 25, 2013 #2

    gneill

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    Staff: Mentor

    Find the current through the 8Ω resistor. What new current can you label on the diagram?
     
  4. Apr 25, 2013 #3
    It's 1 A.Does that mean that the current through R is 3A?
     
  5. Apr 25, 2013 #4

    gneill

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    Staff: Mentor

    Yes. Where does the 3A come from (what other current must be 3A)?
     
  6. Apr 25, 2013 #5
    The one running through 2 Ohm?
     
  7. Apr 25, 2013 #6

    gneill

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    Staff: Mentor

    Yes and no. Certainly the 3 A flows there, but i1 also flows through that resistor. Can you place the 3 A on the appropriate wire leading from the node? Any ideas what you might do with that knowledge?
     
  8. Apr 25, 2013 #7
    I want to find the current in 2 Ohm so I can apply the K's law in the nod...but I dont know how
     
  9. Apr 25, 2013 #8

    gneill

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    Staff: Mentor

    Suppose that you happened to know the potential of that node. Would you be able to find that current then?
     
  10. Apr 25, 2013 #9
    yes.This sounds like a puzzle.I'll have a look at it myself later.Thank you anyway.
     
  11. Apr 25, 2013 #10

    gneill

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    Staff: Mentor

    Good idea :smile:

    As a hint, consider applying nodal analysis at the node (KCL with a bit of KVL thrown in ) :wink:
     
  12. Apr 25, 2013 #11
    O mi god that's what I want thinking! Thanks a lot mate!
     
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