Thevenin equivalent resistance

Thread Starter

AnaLI

Joined Nov 8, 2016
2
Hey, guys,
I'm having a lot of trouble understanding the solution to this exercise:

upload_2016-11-9_2-11-3.png
upload_2016-11-9_2-13-43.png
upload_2016-11-9_2-13-52.png

The goal is to calculate the Thévenin resistance between e and f. The solution is 2.3 ohm. WHY??
I'm pretty sure it's 2.9 ohm.

If someone understands why it is 2.3ohm, can you explain, please? Thanks.
 

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WBahn

Joined Mar 31, 2012
26,398
How are you arriving at 2.9 Ω?

If you zero the sources, what are you left with looking between points e and f?

Don't you have 2.9 Ω in parallel with some other resistance? So isn't the equivalent resistance of two resistances always less than the smaller of the two?
 

Thread Starter

AnaLI

Joined Nov 8, 2016
2
How are you arriving at 2.9 Ω?

If you zero the sources, what are you left with looking between points e and f?

Don't you have 2.9 Ω in parallel with some other resistance? So isn't the equivalent resistance of two resistances always less than the smaller of the two?
You're saying I am to consider the R3 in parallel with (R1+R2+R4+R5)?
Ok, yes, that yields 2.3ohm. I get way too confused when there are ground connections involved...

Thank you, I'm sorry for the trouble. Guess this was a really silly question.
 

Bordodynov

Joined May 20, 2015
2,939
X=(R1+R2+R5+R4)||R3=2.32
Move seats R1 and V2 (the current through R3 will not change). Unite voltage sources. Transfer the ground to the point f (current through R3 will not change). Move the resistors and source. Get the source and four series resistors. Make the conversion and get my formula.
 

WBahn

Joined Mar 31, 2012
26,398
You're saying I am to consider the R3 in parallel with (R1+R2+R4+R5)?
Ok, yes, that yields 2.3ohm. I get way too confused when there are ground connections involved...

Thank you, I'm sorry for the trouble. Guess this was a really silly question.
The ground connection in this case is a complete red herring since nothing of interest is referred to the ground, so it can be ignored.
 
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