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Homework Help: KCL and simultaneus eqs.

  1. Jun 4, 2009 #1
    1. The problem statement, all variables and given/known data

    I am struggling as usual with quite a confusing circuit i need to find i1 i2 and i3 in this circuit using kirchoffs laws

    i know i need 3 loops

    loop 1 is V1...ABCD....V1

    loop 2 is V1...ACD.....V1

    Loop 3 is V1....ABD....V1

    2. Relevant equations

    R1=.5 ohm R2=1 ohm R3=1ohm R4=.5ohm R5=1ohm

    3. The attempt at a solution
    i have worked out loop1 to be

    I1R1-I3R5-(I2+I3)R4 = 1V

    but the other loops look wrong and then i cant seem to use simultaneus equations effectively.

    Any help much appreciated

    Attached Files:

    • KCL.JPG
      File size:
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  2. jcsd
  3. Jun 4, 2009 #2

    The Electrician

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    I can't view your image until it's approved. If you'll upload it to a free image hosting site, and post the link here, I'll be able to view it sooner.
  4. Jun 4, 2009 #3
  5. Jun 4, 2009 #4

    The Electrician

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    The currents you've shown are branch currents, not loop currents.

    The circuit is an unbalanced wheatstone bridge. See:


    If you redraw it to look like a wheatstone bridger, it will be easier to draw distinct loop currents.
  6. Jun 4, 2009 #5
    Hi Electrician

    Thats how i initially approached the question i sent my workings out to my tutor who told me to seperate it into the three loops and then use simultaneus equations to find the unknowns,

    when i did it initially whith the wheatsone bridge approach i got values of 1.5 1 and 05 for the various currents when i do the loops the values in teh equations are mostly .5's and 1s
    and are difficult to multiply out
  7. Jun 4, 2009 #6

    The Electrician

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    Post a new image with the circuit drawn as a wheatstone bridge with 3 loop currents indicated. Show the equations you derived for each loop. Then I can help you.
  8. Jun 5, 2009 #7
    ok will do!

    thanks Ian
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