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KVL application

  1. Apr 15, 2015 #1
    hello

    what is the process to apply KVL exactly?

    we know nothing in a loop, apart from that it consists of 2 batteries with known polarity and 2 resistors.

    what do we do?

    we assign arbitrarily the currents to each of the branches that compose the loop? and then we assign polarities to the resistors?

    or we assign arbitrarily polarities to the resistors in the loop and apply kvl based on that and if we find negative values, we just invert the polarity?

    I am a bit confused

    To give you an example:
    upload_2015-4-15_14-28-19.png

    1) according to the first method (we take resistor polarities based on the arbitrarily taken currents)
    in left loop, we have V1-Vr3-Vr1=0
    in right loop, we have V2-Vr2+Vr3=0
    2) according to the second method (we assign polarities of resistors arbitrarily)
    in left loop, we have V1-Vr3-Vr1=0
    in right loop, we have V2-Vr2+Vr3=0

    which are the same, but the website of this example gives:
    0cbb994040dab97570b92f9b9749960b.png
    and
    4321cdc46d8988dee94d4e54a0d32e97.png

    WHICH IS DIFFERENT!!!!


    thanks
     
    Last edited: Apr 15, 2015
  2. jcsd
  3. Apr 15, 2015 #2

    CWatters

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    Which website?
     
  4. Apr 15, 2015 #3
  5. Apr 15, 2015 #4

    SammyS

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    I think it's just a typo.

    He later writes:
    a94bdc8bc3c8f2088e7080f82db570a4.png

    and
    67ea64f45c29bdc54996286d5d07072b.png

    which implies using opposite signs for VR3 .
     
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