Is it right to consider these resistors in this way? [duplicate]

If we short circuit all voltage sources and consider all the resistors but RL, the same current is flowing though R1 and R2 (they are in series) and they are in parallel with R3 and R4. Is it correct?

What I mean is, by using Thevenin theorem, the equivalent resistor R0 should be:

$$\R_{0} = R_1 + R_2 + \frac{R_3\cdot R_4}{R_3+R_4}\$$

Is this right?

• wait a sec. If you short all sources, then you have no voltage in the circuit. No power source. No currents anywhere.
– Ilya
Commented Feb 16, 2022 at 12:52
• @Ilya well yes but I just wanted to see how the resistors are with respect to each other
– mlp
Commented Feb 16, 2022 at 12:54
• Also, you can't just say "not considering Rl". You need to specify how to not consider. As if it's not there and there is no connection or as if it's not there and there is a short circuit. You probably mean the former, but you should word it correctly and unambiguously.
– Ilya
Commented Feb 16, 2022 at 12:56
• Did you ask a very similar question yesterday or the day before where I made a picture for you to study? If so, then you should reinstate that question or at least embed the picture I made into this question to make it easier for folk to point out a solution. Commented Feb 16, 2022 at 12:59
• Well yes thanks, but the picture did not provide additional information, I already mean that by how I formulated the question I guess. Here it is: [2]: i.sstatic.net/28sa5.png
– mlp
Commented Feb 16, 2022 at 13:23

The whole question makes no sense at all. There is no "parallel" or "series" without any power source. Let me show you a simplified example. Apologize for my paint art. Consider this:

Is this in series? Yes. Is this in parallel? Yes. Depending on where you apply voltage in the circuit (for series you need to break one of the connections and put V source there, just like how you "removed" them).

If you have more resistors or voltage sources, it gets even messier and weirder.

Let's re-draw your problem as you worded it:

Depending on where you apply voltage, R2 and R3 can be in parallel or series.

the same current is flowing though R1 and R2

There is no voltage and therefore there is no current. Your question basically makes fundamentally no sense. When we talk about parallel and series resistors, we talk about current going parallel to each other through them or through one and then through another. You have no current in the circuit. Your question can make sense if and only if there is at least one power source.

EDIT: let me give you one more illustration.
Consider the full circuit:

Are they in series or parallel? "Obviously in series" you will say. And you will be wrong. They are in series only because you imply that the left end is + and the right end is -. Or the other way around. If the "-" is in the middle, then one of the resistors does nothing and is neither in series nor in parallel with the other one. We simply make this implication because it makes most sense for this kind of circuit. But we always imply current flow. In your circuit there are no obvious + and - terminals. In fact, you deliberately removed them all.

EDIT 2: after pulling out more information from the OP in the comments here, turns out the resulting circuit is this:

Where voltage source (NOT generator!) is instead of Rl. Therefore the current (conventional, from + to -) goes via R4, then splits into R1+R2 and R3. So

R0 = R4 + (R3 || (R1+R2))

I'm pretty sure you can turn it into exact formula, you clearly know the formula for parallel resistances.

"As seen from" basically means "imagine voltage source here"

• Thanks but that's not useful at all, I just said we circuit all generators because that's what my professor suggested to look at parallel/ in series resistors. I meant to understand if my interpretation of R0 was correct
– mlp
Commented Feb 16, 2022 at 13:53
• Your formula implies you have a voltage source in such a place that R1 and R2 are in series. You can also place it in such a way that R1 and R2 become parallel and you will have R1 and R2 in fractions and R3 and R4 in series. Resistors themselves don't exist as parallel or series. Currents in them do. And currents are provided with power sources. connected to specific points. We just simplify it as "parallel resistors" when we mean currents going in parallel through the resistors.
– Ilya
Commented Feb 16, 2022 at 13:56
• But I am referring to the picture above, why can't anyone answer me if that's how it is or not?
– mlp
Commented Feb 16, 2022 at 13:57
• R0 is the equivalent resistance, from the Thevenin thereom, seen from the sides of RL
– mlp
Commented Feb 16, 2022 at 14:02
• Thanks a lot!!!!
– mlp
Commented Feb 16, 2022 at 14:16

First of all. You have to find where are you going to apply the thevenin's theroem. Between the two terminals. So I can't find the thevenin's theroem. But for the default case it is across the Load resistance. So It would be ((R1+R2)||R3)+R4