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Use Kirchoff's laws to solve for tension and current

  1. Sep 25, 2016 #1
    1. The problem statement, all variables and given/known datahttp://postimg.org/image/ys43ylstp/
    I need to find tension and current in each element of the circuit. I have included an image of what I have drawn so far for the circuit. http://postimg.org/image/ys43ylstp/

    2. Relevant equations
    Kirchoff's laws.

    3. The attempt at a solution
    I separated it into three loops. The one on the top I called loop 1 and the equation would be:
    -5+R2I2+R1I1=0
    loop 2 is the one underneath:
    15+R3I3-R2I2=0
    and loop 3 is on the far left:
    -15+5+R4I4=0
    Are these the right equations? Whenever I try to use the node law I always mix up something. Can someone please help me solve this problem?
     
  2. jcsd
  3. Sep 25, 2016 #2

    cnh1995

    User Avatar
    Homework Helper

    photo.jpg
    It is better to insert image in the OP itself than posting its link.
    Observe the circuit carefully. You can get all the currents(and voltages) just by inspection and not a single equation is required.
     
  4. Sep 25, 2016 #3
    Sorry about the picture.

    I have been working on it, and I assume that the current going through R1 would be 1.5A and the current going through R3 would be 0.5A.
    I am also thinking that I2 = 1.5-0.5, which will let me calculate the tension for R2.
    Could I combine the 2 voltage sources, as if they were in series, and get a single voltage source of 20V? Then that would be the voltage of R4 and I could calculate the current?
     
    Last edited: Sep 25, 2016
  5. Sep 25, 2016 #4

    gneill

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    Staff: Mentor

    Yes you can sum their potentials in series, however, beware of the polarities of the voltage sources!

    You seem to be doing fine applying KCL where required and filling in the potential drops across the resistors. Keep going!
     
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