Rth for a circuit

• Engineering
GBA13

Homework Statement

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?

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!

Attachments

• Screen Shot 2014-12-16 at 15.49.37.png
4 KB · Views: 364

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?

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 I thought that when Vt has been replaced by a wire (as you do to fine Rth) then all the current can go through the new wire instead?

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...

GBA13
Oh sorry, I'm getting confused with R5. (You can get rid of R5 can't you?)

Mentor
Oh sorry, I'm getting confused with R5. (You can get rid of R5 can't you?)
Yup. Suppressing the voltage source shorts out R5, so their combined resistance is 0 Ohms.

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? :)

Mentor
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? :)
Yes!

GBA13
GBA13
Yes!

Yay! Thanks very much! :D