# Find Thevenin resistance

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

1. ### screen1988 Thread Starter Member

Mar 7, 2013
310
4
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 = ∞ ???

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2. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,585
1,285
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
4
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
4,585
1,285
I've got the same answer as you.