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!

Kirchhoff law problem

  1. Mar 2, 2016 #1
    1. The problem statement, all variables and given/known data

    https://fbcdn-photos-c-a.akamaihd.net/hphotos-ak-xft1/v/t1.0-0/s480x480/12802893_10205707400875867_4855727067132215897_n.jpg?oh=b486598e6f2016a814eb52bf48870334&oe=57648CD9&__gda__=1464637082_3cae40328f43f09eaa2cf9cf5b2f0b0f
    2. Relevant equations
    Kirchhoff Law
    1. Find the current in the circuit
    2. Find the potential diferent between X and Y
    3. The attempt at a solution

    1 by using the kirchoff law. V=IR
    I=0.025

    question 2 I=0.025
    but how to find Vx and Vy?
    Vx =IR
    I =0.025 but which R is supposed to use?
     
  2. jcsd
  3. Mar 2, 2016 #2

    cnh1995

    User Avatar
    Homework Helper

    Your current direction is correct. One way to solve this problem would be by assigning potentials and calculating voltage drops. Assume potential of point W to be 0V. That way, +ve terminal of 20V source will be at 20V. Then calculate drop across 40 ohm resistor. Point x will be at 20-V40Ω potential. Go on with this along the loop and find potential of point y. Difference between them is your Vxy.
     
  4. Mar 2, 2016 #3
    Thanks!! I got it
    https://scontent-kul1-1.xx.fbcdn.net/hphotos-xlt1/v/t1.0-9/12814145_10205707617681287_7591958914593573074_n.jpg?oh=b9163aaa1c77737cb533a124e4292d6a&oe=574F8189

    By using kirchoff law i get all the current
    the question ask to find the PD between A and B, the question is the voltage drop i should begin in which point? Because there is 2 sources
     
  5. Mar 2, 2016 #4

    cnh1995

    User Avatar
    Homework Helper

    You can start by either assuming A at 3V or assuming B at 0V. Since you know i1, assuming B at 0V will be easier.
     
  6. Mar 2, 2016 #5
    But point A is supplied by 2 battery of 3V.If i use voltage drop, I only need to look at the top loop?
     
  7. Mar 2, 2016 #6

    cnh1995

    User Avatar
    Homework Helper

    You need to find the currents using the two loops (which will include both the sources) and then by assuming a suitable reference( VB=0V), you can find Vab like you did in the last problem.
     
  8. Mar 2, 2016 #7
    if i assume Vb =0
    -6(I2)+3V=Va?
     
  9. Mar 2, 2016 #8

    cnh1995

    User Avatar
    Homework Helper

    -6I1+3V=Va..
     
  10. Mar 2, 2016 #9
    Ops mistake haaha. thank you , have a good day!
     
  11. Mar 2, 2016 #10
    https://scontent-kul1-1.xx.fbcdn.net/hphotos-xft1/v/t1.0-9/12814383_10205707793045671_2997254212403029818_n.jpg?oh=0a9ed6d9fbec4f8eed32f88ffdfba9b1&oe=57574AC1

    If Vx is 0 , what is the V in point Y
    -12(I1)-8(I2)=Vy
    which i will gef -12V in Y, is this possible for me to get 12V in negative value?
     
  12. Mar 2, 2016 #11

    cnh1995

    User Avatar
    Homework Helper

    Yes. In fact you don't even need to know the current for that. Moving from x to y along the bottom wire, you can see a voltage drop of 12V.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Kirchhoff law problem
  1. Kirchhoff's Law Problem (Replies: 18)

  2. Kirchhoff law problem (Replies: 11)

Loading...