Thevenin resistor question

Discussion in 'General Electronics Chat' started by acelectr, Sep 4, 2010.

  1. acelectr

    Thread Starter Member

    Aug 28, 2010
    Hi, I've started to work on thevenin's theorem and I didn't really get the thevenin resistor part. What I've read was when calculating this resistor you remove the load and the power sources etc. and calculate the resistance between the two points of where the load was removed bla bla bla. What I didn't get was that shouldn't a resistor value needs to be infinite between two points where there is nothing but air. When you remove the load, the resistance, as far as I know, needs to be infinite but as it is seen thevenin resistor gets different values by calculating the amount of other resistances in parallel. How come it is not infinite? What's the logic behind this and the logic behind of getting the thevenin resistor by taking the resistance of other resistors in parallel? (Hope I explained my problem clearly)

    Thanks for any help
  2. Ghar

    Active Member

    Mar 8, 2010
    Basically you're finding the resistance 'seen' by the load.

    You're taking the point of view of the load - what does the load see when connected to this circuit?
    If you attach a current source instead of a resistor at the load what voltage will you generate?
    acelectr likes this.
  3. debjit625

    Well-Known Member

    Apr 17, 2010
    Its like this ,Lets we have three resistor (R1,R2,R3) connected in a loop.Now if you remove one of them from the loop and measure between two point from where the resistor was removed you will find the series resistance of another two resistors.This is what happens in Thevenin's circuit and the removed resistor is called the Load resistor.
    Thevenin's theorem is nothing more than to solve a complex network to a voltage source with a series resistor connected with it.

    Good Luck
    acelectr likes this.

    New Member

    Sep 5, 2010
    You might have noticed in Thevenin's equivalent circuit, that the resistance you omitted earlier while solving is attached again in the equvalent circuit as the load. So its not like we have to find resistance between the two points but we have to see from the direction of the omitted load that what could be the thevenin equivalent resistance by th perspective of the load. Hope I made it clear. Enjoy solving.
  5. PackratKing

    Well-Known Member

    Jul 13, 2008
    Thevenin Schmevenin !! :D

    Ohms' Law is adequate to the task at hand. Thevenins' terminology and approach just tend to cloud the issue. My humble 2 cents worth.
    Last edited: Sep 5, 2010