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I understand that here, the current has a choice to flow through one resistor and back to the terminal WITHOUT going through the other.

enter image description here

Is this, a parallel circuit? I don't get it. Sorry if this is dumb, I'm really confused. There ARE junctions, which means the current has a "choice" to flow through the resistor, or just go on. But WILL it flow through them at all? All this is messed up.

How is this a parallel circuit?

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  • $\begingroup$ When you connect two terminals of a resistor with a conducting wire, then no potential difference exists and hence the current though it will be zero. In both diagrams, no current will pass through the resistors when the conducting wire is of negligible resistance. $\endgroup$
    – Vishnu
    Commented Feb 22, 2020 at 10:36
  • $\begingroup$ Why (or how do you know) that potential difference doesn't exist? $\endgroup$
    – El Flea
    Commented Feb 22, 2020 at 10:44
  • $\begingroup$ WILL electricity flow through them at all? In theory, where the wire resistance is zero, it will not flow through the resistors. In practice yes, a small amount will flow through them depending on the value of the resistors and the resistance of the wire. $\endgroup$
    – Leo
    Commented Feb 22, 2020 at 10:55
  • $\begingroup$ @Leo So does that make it a parallel or series circuit? $\endgroup$
    – El Flea
    Commented Feb 22, 2020 at 11:52
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    $\begingroup$ It looks like you are at a pivotal point in your education where how you thought about circuits initially was useful, but now it's time to shift how you view them. Thinking in terms of the "choice" of the current seems quite confusing and not very rigorous. $\endgroup$
    – BioPhysicist
    Commented Feb 22, 2020 at 13:59

3 Answers 3

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I'd suggest dropping the name "parallel circuits" and starting to think of parallel loops or components in parallel. Indeed, early physics courses sometimes teach a quite misleading view that there are only parallel circuits and series circuits, whilst actually most circuits you will come across will have a combination of components in both parallel and series!

When two loops are connected in parallel, it just means that the endpoints of the loop are connected to the same nodes. What is a node? The circuit below represents different nodes in different colours:

enter image description here

The two resistors on the right of the diagram below are connected in parallel, for instance. The ends of both are connected to the same nodes!

Furthermore, if the potential at one of the nodes is $V_{a}$ and the potential at the other node is $V_{b}$, it should be fairly evident that both loops have the same potential difference across them, $V_{a}-V_{b}$.

Now to answer your specific question. Look again at the second circuit diagram you drew. The ends of the resistors are clearly not connected to the same nodes, so they can't be in parallel! Both are however connected in parallel with a section of wire, which is slightly odd...

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  • $\begingroup$ "The ends of the resistors are clearly not connected to the same nodes, so they can't be in parallel!" That's what I can't see. Isn't the "main" wire that goes straight from one end of the power supply to the other considered a "node"? Or are you saying that EACH terminal should have a separate node? Because in my diagram, BOTH terminals of BOTH resistors have the SAME node. $\endgroup$
    – El Flea
    Commented Feb 22, 2020 at 10:52
  • $\begingroup$ No, consider the short circuit wires as circuit elements themselves. It's quite unusual for them to be included, but for sake of understanding that's what I'd suggest. $\endgroup$
    – 13509
    Commented Feb 22, 2020 at 11:07
  • $\begingroup$ By short circuit wires, do you mean the ones between the fat circles (junctions) in my diagram? Or do you mean the wires that connect each resistor to the "main" wire? $\endgroup$
    – El Flea
    Commented Feb 22, 2020 at 11:51
  • $\begingroup$ @ElFlea I'm referring to the wires between the fat circles. $\endgroup$
    – 13509
    Commented Feb 22, 2020 at 12:09
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In real life each wire has a finite resistance. Only super conductors have zero resistance. So your second figure should actually look like enter image description here Then there is no question that there are multiple paths for current to flow.

However now let us consider the hypothetical ideal case where the wires have zero resistance. Then for the junction the effective resistance also becomes zero. This implies that the current flow will be such that there is no resistance. This can only happen in the wire path and not the resistor path. Thus all current will flow only in the wire path and none in the resistor path.

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  • $\begingroup$ I never realized, this actually solved my question! $\endgroup$
    – El Flea
    Commented Mar 8, 2020 at 15:05
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They are neither in series nor in parallel.

For two elements to be in series :- There should be one ordinary node between the two elements but here there is one extra ordinary node between them.

For two elements to be in parallel :- They should have 2 extra ordinary node in common but here they have only one extraordinary node in common.

Ordinary node :- node which connects 2 elements.

Extraordinary node :- node which connects more than 2 elements

Note :-

If you are wondering how it's an extraordinary node when their are only 2 elements, assume a voltage source between the two terminals across which you are trying to figure out if the elements are in parallel or series. So you have 3 elements in total in this circuit

Two elements may be in series/parallel/neither depending on across which two two terminals you are finding out.

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  • $\begingroup$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Commented Aug 25, 2022 at 8:04

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