Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Please help Circuit analysis (Thevenin voltage and internal resistance)

  1. Oct 3, 2006 #1
    URGENT!! Please help!! Circuit analysis (Thevenin voltage and internal resistance)

    Hi guys,
    I am really stuck on this portion of my lab and it's due tomorrow!! Please help!

    I have two questions:
    The first deals with the diagram from the left of the attached picture. I have to prove that RI (internal resistance of the meter movement) is equal to (RS)(RP)/(RS-RP). I tried reducing the circuit through circuit analysis (Rs = R1+R2+... and 1/Rp=(1/R1)+(1/R2)+...) but it doesn't work. Please give me some pointers, thank you.

    The second question is about the circuit on the right. I have to find the Thevenin voltage for this circuit. I know this is equal to the open circuit voltage which I measured to be 0.790V in the lab. I found the Thevenin resistance to be RTH=1,500 Ohms by circuit analysis. Please give me some ideas on how to solve for VTH, thank you!

    Attached Files:

    • lab.GIF
      File size:
      4.5 KB
  2. jcsd
  3. Oct 3, 2006 #2
    Don't know what the circuit looks like, but the procedure for finding the look in resistance is to turn off all your sources. Open circuit your current sources and short circuit your voltage sources.

    You can solve for the Thevenin voltage by finding the short circuit current at the load terminals.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook