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Kirchoff's Loop Rule

  1. May 2, 2006 #1
    I have a diagram on my website and I also attached it to this message. My question is I am wondering if my equation for this loop rule is correct. I am trying to solve it but I am having a problem about the signs I am getting..

    This is my equation for this loop:


    [tex]I_2=I_1+I_3[/tex]

    [tex]6V-2I_3-2I_2=0[/tex]

    [tex]1V-2I_3-I_1=0[/tex]

    Do you think the above equations are correct?I used the equations but I get different signs that doesn't match the circuit on the diagram...

    This is the site of the circuit: www.geocities.com/willydavidjr/loop.html
     

    Attached Files:

    Last edited: May 2, 2006
  2. jcsd
  3. May 2, 2006 #2

    berkeman

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    Staff: Mentor

    Last equation is +I1. Look at the voltage *increase* through R1 in that direction due to I1.
     
  4. May 3, 2006 #3
    I see. Do you think berkeman the second equation should be 6V - 2I3 + 2I2=0? What do you think?
     
  5. May 3, 2006 #4
    I don't think that the third equation should be +I1. Because we will get negative answer for I3 and I1. Meaning they have opposite direction and it shouldn't be!
     
  6. May 3, 2006 #5

    Curious3141

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    Homework Helper

    The second equation is fine as you wrote it (why do you think the sign is wrong ?). Just amend the third equation as berkeman suggested.

    When taking a loop across a resistance, if going with the labelled flow of current, use the minus sign. If going against the labelled flow of current, use the plus sign.
     
  7. May 3, 2006 #6
    Berkeman what I get for this three equation just as I amended the 3rd equation are I1= 1 amp, I2= 1 amp and I3= 1 amp. Am I correct? I expected to get a negative value for I1 but I didn't get it. All have positive values. Do you think all flow of currents are correct?
     
  8. May 3, 2006 #7

    berkeman

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    Staff: Mentor

    How can they all equal 1A when your first equation says I2=I1+I3 ?

    When you get the answers, just go back and put them on the original drawing, and see if all the voltages and currents add up.
     
  9. May 3, 2006 #8
    No I mean 2A for I2. Sorry my fault.
     
  10. May 3, 2006 #9

    Curious3141

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    Homework Helper

    I replied to your PM. The answer is correct.
     
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