# R_th wrong while applying series and parallel simple theory

Ohmslaw
Summary:: Trying to find Rth but I do not get the same value as the one from the solution.

[moderator: moved from a technical forum. No template.]

I am trying to find Rth to solve this problem, however once I simplified it, I get a value of 700.745 Ω while in the solution, the answer is 1.161kΩ. How is that possible ? What goes in parallel and what goes in series ?

Thank you !

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Asymptotic
1. This looks like a homework question. It ought to be posted in that forum.
2. Is your simplification from the perspective of R3?
When I calculate the resistive network from the perspective of R3 it works out to 1.161K

Gold Member
It looks like you almost had it. My recommendation would be to move that ground so it's easier to interpret. Let's say we move it to where the V- is and draw the old ground as wires connecting to each other?

I'm not solving it for you... just redrawing it in a different way :) Would this be okay for you?

hutchphd, etotheipi, Asymptotic and 2 others
alan123hk
I get a value of 700.745 Ω

Based on your circuit diagram, it seems that you have found the equivalent resistance of the terminal (+) with respect to ground instead of the equivalent resistance of (+) with respect to (-).

hutchphd and Asymptotic
I believe the battery is drawn with positive ground.

Mentor
Assuming the circle with the arrow is an amperemeter: R5 is in parallel with it, so it doesn't do anything. You get three parallel resistors and then R1 and the voltage source as separate elements.

Homework Helper
2022 Award
That's a current source, I believe.

Mentor
Suppress the sources and you get something like this:

Homework Helper
2022 Award
When I calculate the resistive network from the perspective of R3 it works out to 1.161K
Including R3, right?

Gold Member
1. This looks like a homework question. It ought to be posted in that forum.
2. Is your simplification from the perspective of R3?
When I calculate the resistive network from the perspective of R3 it works out to 1.161K
Including R3, right?

That answer will include R3. I think a few people have answered this question :)

Homework Helper
2022 Award
The phrasing seems odd to me. "From the perspective of R3" would seem to exclude R3 from the Thevenin. Semantics...

Gold Member
I agree: It makes R3 sound like the load. I solved it just to be sure.

Asymptotic
The phrasing seems odd to me. "From the perspective of R3" would seem to exclude R3 from the Thevenin. Semantics...

"Perspective" was the first word that came to mind (at least, to my mind) that conveyed the essence of "Rth across R3".

Perspective, in the sense of "the combination of me, and all those connected to me". By that definition, network resistance from the perspective of R1 is 700.75Ω, from R3 is 1160.81Ω, and from R5 is 1361.02Ω.