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Homework Help: Kirchhoff's circuit laws

  1. Feb 20, 2008 #1
    1. The problem statement, all variables and given/known data

    http://img207.imageshack.us/img207/1685/p1854altco4.gif [Broken]

    Find the unknown emf and the unknown currents in the circuit below, in which R = 3.48 . Take the positive direction for current flow in each branch to be upwards.
    EMF = V
    left branch= A
    right branch= A

    2. Relevant equations

    Kirchhoff's circuit laws

    3. The attempt at a solution

    I added current lines to the diagram. Note that a coordinate system is imposed and all positive charges point up ( I guess this makes grading easier). I sketched the lines of current as best I could.

    Here are my equations:

    Left loop:


    Outside loop:

    1.00v-3.48I1-1.00I3+1.20V+4.00I3=0 (edit: caught a mistake here, last term should have been positive)

    Apply junction rule to top center junction:

    Combine terms:

    Substituting I1+.05 for I3:


    Combining like terms:


    I1(the left loop)=4.90A which is wrong.

    Any ideas where I messed up?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Mar 20, 2010 #2
    Where is the circuit diagram???????????????
  4. Mar 20, 2010 #3
    Blast from the past! I have since moved past physics and on to medicine so things worked out well enough I suppose.
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