Find Thevenin resistance

Discussion in 'Homework Help' started by screen1988, Apr 13, 2013.

  1. screen1988

    Thread Starter Member

    Mar 7, 2013
    310
    3
    Today, I get stuck in finding Thevenin resistance for the circuit in attached file.
    The circuit has I0=2A, Z= 2Ω, R1=2Ω, R2 =4Ω.
    To calculate Thevenin resistance, I connnected port A with 4V voltage source.
    I2 = 4V/R2= 4V/4Ω = 1A
    Apply KVL for the closed path R1, R2, Zi:
    4 = Z*i + R1*i= 2i + 2i =4i
    => i = 1A
    Apply KCL at A:
    I1 = I0 - i = 2A- 1A=1A
    Apply KCL at B:
    I3 = I2 - I1 = 1A -1A =0
    => Rth = 4V/ I3 = 4/0 = ∞ ???
    I don't know where I am wrong here? Please help.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    You answer looks good, But what you found is not a Rth. To find Rth you need to replace Io current source with a open circuit.
     
    screen1988 likes this.
  3. screen1988

    Thread Starter Member

    Mar 7, 2013
    310
    3
    Oh, thanks Jony! I see it. I don't know why I forgot it!
    Yes, with current source open, I can easily find Rth = 2Ω now.:)
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    I've got the same answer as you.
     
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