# How do I calculate total resistance?

As far as I understand, two resistors are connected in parallel if the node at both ends of both resistors are the same. And in series if only one node is the same.

But what if between two resistors there is/are some component(s) like Voltage Source, Current Source, Ammeter, etc?

For example in this circuit:

The R2 is parallel to the R3. $$=> R_{23} = R_{2} || R_{3}$$

But after that, the R1 is parallel or in series to R23? And why?

And if there was no current source, would it change the relationship between R1 and R23?

Thanks.

• In this case is neither in parallel and neither in series. Rtotal = R1||(E/J)
– G36
Commented Dec 8, 2018 at 18:13
• Can you explain how did you come up to that conclusion that it's neither in parallel nor in series? Would be helpful to me. :)
– weno
Commented Dec 8, 2018 at 18:19
• J is infinite impedance in series with R23 so the equivalent or right hand half loop Z=E/J while E is a 0 Ohm source on the left Commented Dec 8, 2018 at 18:38
• They picked annoyingly non-neutral names for their current sources- E which is often used for voltage and J which is often used for current density. Commented Dec 8, 2018 at 19:57

$$\R_1\$$ is neither parallel nor in series with $$\ R_2||R_3 \$$. You have to apply KCL and KVL to find the resistance seen by E or J current sources. If there is no current source J and the branch is shorted, then $$\R_1\$$ would be in parallel with $$\ R_2||R_3 \$$.