Rth for a circuit

1. Dec 16, 2014

GBA13

1. The problem statement, all variables and given/known data
Hi,

I am trying to find Rth for this circuit but Im not sure if I've got it right, could someone give a hand?

2. Relevant equations

3. The attempt at a solution
I think R3 can be omitted and R1, 2, and 4 are in series so the answer is 10k Ohms as R5 is in parallel to what was the power source (now a wire) can be omitted as well?

Thanks!

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2. Dec 16, 2014

Staff: Mentor

R3 cannot be omitted as there is no path from A to B that can avoid it.

What's the procedure for finding the Thevenin resistance of a circuit?

3. Dec 16, 2014

GBA13

Really? I thought that when Vt has been replaced by a wire (as you do to fine Rth) then all the current can go through the new wire instead?

4. Dec 16, 2014

Staff: Mentor

Inject a current at A and show how it can get to B without passing through R3. Shorting the voltage supply (replacing with a wire) does not make a difference there. It does, however, let you eliminate another resistance...

5. Dec 16, 2014

GBA13

Oh sorry, I'm getting confused with R5. (You can get rid of R5 can't you?)

6. Dec 16, 2014

Staff: Mentor

Yup. Suppressing the voltage source shorts out R5, so their combined resistance is 0 Ohms.

7. Dec 16, 2014

GBA13

So then R1 and R4 are in series and that pair is in parallel to R2. That whole combination is then in series with R3 to make Rth 5.4 k Ohms? :)

8. Dec 16, 2014

Staff: Mentor

Yes!

9. Dec 16, 2014

GBA13

Yay! Thanks very much! :D