Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Need help with Kirchhoffs Loop Law

  1. Jan 22, 2007 #1
    I am a grade 11 student in Canada. I have an exam in 3 days and i cannot figure out how to solve a cricuit with several loops... i have been told that for this specific cricuit i can use Matricies or Substitution. I dont know anything about Matrices and im having trouble substituting with three equasion and three unknows... i have attached a schematic diagram, it is simalar to a wheatstone bridge and is called an H-bridge. could someone plz help me solve this...

    Attached Files:

  2. jcsd
  3. Jan 22, 2007 #2


    User Avatar

    Staff: Mentor

    Thread moved to the homework forums. Baioff, one of the rules here on the PF is that on homework/exam questions like this, you must show us your work in order for us to help you. Tell us what you do know about writing the KCL or KVL equations. If you write out the equations, it's pretty easy for us to give you some hints on how to solve a set of 3 linear equations in 3 unknowns (if that's what results).
  4. Jan 22, 2007 #3
    Ok srry about that
    1. The problem statement, all variables and given/known data
    circuit attached above... Vt, and all resistances will be given

    2. Relevant equations
    Matrix algebra ???

    3. The attempt at a solution
    well i was shown the following by a physics tutor who was only partially knowlegable on the subject. (resistors labled 1-5 1 being top left 2 top right 3 middle 4 bottom left and 5 bottom right)

    0=I2R5+I5R3 - I3R4
    0=I1R5+I5R3+I6R1 +v



    I5(R3+R4+R5) =I6R5-I4R5
    I5R3=I6(-R5 - R1) -I4R5 - V

    I think thats right... but if someone could elaborate on how to decide appon the I number and how they relate to the resistors and possibly an easier way of solving this.
    Last edited: Jan 22, 2007
  5. Jan 22, 2007 #4
    its simple jus assume currents 1 2 3 flowing in threee diff loops
    then jus write 3 equations n if a resistor is appearing in 2 circuits take it like
    sum of both according to the direction multiplied with resistance which equals voltage
    n take net sun of voltages in the loops equal to 0
    now for solving the equations u can use matrices or substitution
    method which is of ur choice depending on ur ease with the matrices concept
  6. Jan 23, 2007 #5


    User Avatar

    Staff: Mentor

    First, it would help if you could label the resistors in your sketch. That would make it easier to follow your equations and then suggest ways to reduce the equations.

    In addition, are you required to use the KVL loop equations to solve this problem? If not, I find the KCL node voltage equations much more intuitive to work with.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook