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Find the current

  1. Sep 5, 2013 #1
    1. The problem statement, all variables and given/known data

    Find the current marked I3 in the circuit.

    2. Relevant equations



    3. The attempt at a solution

    The voltage over R2 and R1 is the same. The current I0 (12mA) is the sum of I2 and I1.

    I1*R1 = I2*R2:
    4*I1 = 1.25*I2

    I1 + I2 = 12 <=> I2 = 12 - I1

    4*I1 = 1.25*(12 - I1) = 15 - 1.25I1
    5.25*I1 = 15

    I1 = 2.86

    I think I've messed up already here. Can anyone spot what I'm doing wrong??
     

    Attached Files:

  2. jcsd
  3. Sep 5, 2013 #2

    ehild

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    Homework Helper
    Gold Member

    It is wrong. The voltage over R3 and R4 is the same .

     
  4. Sep 5, 2013 #3
    Thanks! Is I2 still the sum of I3+I4 though? :S
     
  5. Sep 5, 2013 #4

    gneill

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    Staff: Mentor

    Sure.
     
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