1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question on Kirchoff's Laws

  1. Feb 9, 2012 #1
    I was hoping someone could help out, I am working out a problem with Kirchoff's Laws and cannot seem to get the math to work out properly, at least I think the math is not working properly.
    I was hoping to run it by someone here.

    1. The problem statement, all variables and given/known data

    The circuit is as follows:
    A battery of 24 V on one end connected to two parallel resistors with values of 5 Ω and 7 Ω.
    Mesh one will be the loop between the battery and the 5 Ω resistor, which has a current of I1.
    Mesh two will be the loop between the 5 Ω resistor and the 7 Ω resistor, which has current of I2.

    2. Relevant equations
    The equations I set up are as follows:
    0 = -24 + 5*(I1 - I2)
    0 = 7*I2 + 5*(I2 - I1)




    3. The attempt at a solution
    After calculating the values I obtained these numbers:
    I1 = 8.229 A
    I2 = 3.429 A

    I tried verifying these answers by using V = I*R
    Finding Req to be 2.917 Ω.
    Therefore I = V/R and I = 8.228 A and since the current from I1 is the same value it seems that the values obtained from Kirchoff's Laws do not match the Ohm's Law current.

    I am uncertain if I am not realizing a concept but this does not make sense to me.

    Any help is appreciated.
    Thank you,
    A.B.
     
  2. jcsd
  3. Feb 9, 2012 #2

    Delphi51

    User Avatar
    Homework Helper

    I think your work is all correct. V =IR finds the current through the resistors as 4.8 and 3.42 representing I1 - I2 and I2, so I2 = 3.42,
    I1 - I2 = 4.8
    I1 = I2 + 4.8
    I1 = 3.42 + 4.8 = 8.23
     
  4. Feb 10, 2012 #3
    thank you for your help Delphi, sorry I posted in the wrong area.
    I think I understand now,

    A. B.
     
  5. Feb 10, 2012 #4

    Delphi51

    User Avatar
    Homework Helper

    Most welcome! This is the correct area for your question.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question on Kirchoff's Laws
Loading...