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: Thevenian theorem

  1. Jan 26, 2009 #1
    This question is based on the thevenian's theorem,but my problem is on the basic rule of circuit.I have come at the stage where I have to calculate the Thevenian's voltage that is "V" across A and B.I know that V=I*6 since V across AB equals to the V across CD as there is no drop of current on the 3 ohms resistor but now I have to calculste I which can be found by V/R(total).V is 36 volt.Now I have to find Total R which is the stage where I am totally confused since I just know how to rearrange the given circuit.I don't know which one is parallel or in series with another.Please have a look on the picture (which is messy).
    Your post is valuable or me.
     

    Attached Files:

  2. jcsd
  3. Jan 27, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The Thevenin voltage is the open circuit voltage between the terminals A & B. Since you already realize that the 3 Ω resistor is irrelevant, just ignore it. You have a simple series circuit, for which you can find the total resistance and then the current. Use that to find the Thevenin voltage.
     
  4. Jan 29, 2009 #3
    Thanks,I used the voltage divider rule and got the answer.
     
  5. Jan 29, 2009 #4
    This is another type of question where I am troubled to calculate the thevenian voltage.The original question is to calculate the current through 10 ohms resistor.
     

    Attached Files:

  6. Jan 29, 2009 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Once again, the Thevenin voltage is the open circuit voltage between A and B. That means there's no current through the 8 Ω resistor (but don't neglect the 12 V battery). Use the voltage divider rule to find the voltage across the 2 Ω resistor.
     
  7. Jan 31, 2009 #6
    Yeap I really don't know how to treat 12 V battery.
     
  8. Jan 31, 2009 #7

    Doc Al

    User Avatar

    Staff: Mentor

    It's in series with the Thevenin voltage. (But oppositely oriented.)
     
  9. Feb 1, 2009 #8
    Can you give some more hint please........
     
  10. Feb 3, 2009 #9

    Doc Al

    User Avatar

    Staff: Mentor

    Do this: Find the Thevenin voltage just before the 12 V battery. Then you can add the 12 V battery in series with it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook