1. Not finding help here? Sign up for a free 30min 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!

Help with Thevenin Theorem

  1. Jan 17, 2015 #1
    1. The problem statement, all variables and given/known data

    The circuit looks like this: http://i.imgur.com/QtgiCdR.png

    R1= 10 Ω
    R2= 8 Ω
    R3= 3 Ω
    R4= 5 Ω
    R5= 2 Ω

    V= 15 V

    I'm trying the find the current in R1 by using Thevenin's Theorem.

    2. Relevant equations

    Basic Circuit Analysis Formulas

    3. The attempt at a solution

    So I calculated the voltages at the points where R1 is removed. 15V on the left side and 90/101V on the right side (confirmed by LTspice). Then I tried to calculate the Thevenin resistance which (once the voltage source is shorted) is the R2 || R3 || (R4 + R5) which turns out to be 168/101Ω. So putting everything together now, Vth = 15 - 90/101 and Rth = 168/101 and Rl = 10, I get that the current in R1 is 1.2096A but according to LTspice, it should be 1.22003A. What am I doing wrong?
     
  2. jcsd
  3. Jan 17, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Rounding error?
    With Kirchhoff's laws, I get 270/73 V and 1635/584 V for the voltages at the two points (relative to negative source connection, first value at resistors 2/3/4) and 1425/1168 A which is about 1.220034 A as current through R1.
     
  4. Jan 17, 2015 #3

    gneill

    User Avatar

    Staff: Mentor

    Check your evaluation of Rth. Note that R4 and R5 are not in series in this case, since their junction feeds the load terminal.
     
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: Help with Thevenin Theorem
  1. Thevenin's Theorem (Replies: 175)

  2. Thevenin's theorem (Replies: 7)

Loading...