Find voltage between two nodes

  1. 1. The problem statement, all variables and given/known data
    Find voltage between node 1 and node 2


    2. Relevant equations
    What is the algorithm?


    3. The attempt at a solution
    R1=4 Ohms
    R2=5 Ohms
    R3=8 Ohms
    R4=3 Ohms
    R5=6 Ohms
    R6=7 Ohms
    Eэ=20 V
    E3=17 V
    E5=15 V
     

    Attached Files:

  2. jcsd
  3. use balanced wheat stone bridge thing
     
  4. Do I need second Kirhgoff rules' equations for every loop?
     
  5. tiny-tim

    tiny-tim 26,054
    Science Advisor
    Homework Helper

    hi builder_user! :smile:
    (Kirchhoff!)

    'fraid so! :wink:
     
  6. What's the next step after Kirchgoff's rules?What do I need to find?I know current in every branch.
     
  7. gneill

    Staff: Mentor

    You want the voltage between nodes 1 and 2. Use the current you found for the first loop (leftmost) using Kirchhoff to determine the voltage across R1. Then do the obvious voltage sum.
     
  8. i1=3.7A

    U=Eэ-i1*R1=5.2V?

    And the final result -- 20(Eэ)+5.2(U)=25.2V?
     
    Last edited: Mar 24, 2011
  9. gneill

    Staff: Mentor

    That's not the value I get for i1. Better check your derivation.

    EDIT: My error. Redoing my sums I see that i1 is indeed about 3.7A.
     
    Last edited: Mar 24, 2011
  10. Ok.But what's the next?
     
  11. gneill

    Staff: Mentor

    The next what? :confused: Wasn't it the voltage between nodes 1 and 2 that you were looking for?
     
  12. but i's only I1.
    Or R1*I1 - is the result?
     
  13. gneill

    Staff: Mentor

    Very sorry. I see that your figure of 3.7A for i1 and about 5.2V for the voltage between nodes 1 and 2 look okay.
     
  14. A-a-a-a-a!OMG!I'm already started to do all my work from the beginig...It's about 15 pages A4!
     
  15. gneill

    Staff: Mentor

    Again, sorry about that.

    15 pages of A4? That seems like a lot for just three loops. What method are you using to solve the equations?
     
  16. It's a big work like coursework.I have 8 exercises need to do with this scheme(different trasformations like triangle-star and different methods of finding currents like method of equivalent generator(I don't know how does it called in English.translate from russian),node voltage method and etc.).And another 7 schemes.One of them is my previous topic's scheme.

    I got this result(3.7) by different methods.So if it's wrong - all my work is wrong
     
    Last edited: Mar 24, 2011
  17. gneill

    Staff: Mentor

    I see, so this is just one exercise for the given schematic.

    It seems to me that a KVL loop approach is the most straight forward for this particular question, since you really only need to solve for the current in the first loop. Have you learned the method to directly write (by inspection) the matrix form of the equations? That allows you solve for the currents using a matrix method (such as Cramer's Rule), which takes only a few lines.
     
  18. if it's cramer's method...
    I know this method but I only use it in programming.I solve all equtations in MathCAd.And then I show result without numbers and then the final result.The result without numbers is very big sometimes.
     
    Last edited: Mar 24, 2011
  19. gneill

    Staff: Mentor

    Okay, even better.

    Attached is an example, using MathCad, of solving the loops by writing the loop equations in matrix form (which can be done by inspection, and is (almost) foolproof). It's very quick.
     

    Attached Files:

  20. Intersting.I didn't know about it in Mathcad
    all results are the same as the results in my method of countour currents

    thank you for your help.
     
    Last edited: Mar 24, 2011
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