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How do I find the current in this circuit?

  1. Oct 27, 2014 #1
    < Moderator Note -- thread moved from the EE forum to the Homework Help forums >

    Please view the attached.

    The answers are:
    i1 0.1429
    i2 0.4286
    i3 0.2857

    So how do I work this out? I assume you use kirchoffs current law, can someone show me the step? Thanks :)
     

    Attached Files:

    Last edited by a moderator: Oct 28, 2014
  2. jcsd
  3. Oct 27, 2014 #2
    For loop I we can write this KVL
    10V - I1*R1 - (I1 + I2)*R3 = 0
    And for loop II
    20V - I2*R2 - (I2 + I1)*R3 = 0

    Solve this for I1 and I2. And from KCL I3 = I1 + I1

    http://www.wolframalpha.com/input/?i=10 - I_1*10 - (I_1 + I_2)*40 = 0 , 20 - I_2*20 - (I_2 + I_1)*40 = 0 solve I_1 and I_2

    Or we can use nodal analysis.
    For node A we can write a KCL
    I1 + I2 = I3

    I1 = (10V - VA)/R1
    I2 = (20V - VA)/R2
    I3 = VA/R3

    And solve for VA voltage.
    http://www.wolframalpha.com/input/?i=(10 - a)/10 + (20 - a)/20 = a/40
     
    Last edited: Oct 27, 2014
  4. Oct 28, 2014 #3
    thanks mate
     
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