How to find the total equivalent resistance for a circuit? [closed]

RT is the total equivalent resistance. The thing is, can you actually turn the resistances for each circuit into a single equivalent resistance? And how?

For c) I see that the two 4 ohm resistances are in parallel so i turned them into their equivalent resistance (Re) of 2 ohm. But then that equivalent resistance (Re) and the 10 ohm resistance are not in neither parallel nor in series (as far as i understand).

I think they're not in series because the node that connects Re and the 10 ohm resistance is also connected to a terminal (which could be connected to anything). And they're also not in parallel cause they're not connected to the same two nodes. So for a) I think i would end up with Re and 10 ohm resistance, not a total equivalent resistance. But I don't know if i'm right.

• which could be connected to anything ... it is not connected to anything ... that makes the terminal not part of the circuit because it carries no current Commented Aug 24 at 22:36
• Sorry, I meant c). Commented Aug 24 at 22:36
• So what would be the total equivalent resistance of c)? Commented Aug 24 at 22:38
• I think your understanding is wrong. Why would not the 2 ohms be in series with 10 ohms? Commented Aug 24 at 22:52
• use a pencil to draw the path of the current through the circuit Commented Aug 24 at 22:54

A useful tool that you can use is this. Try building your circuit and sending 1V across the two input terminals of the circuit. Now using Ohm's law you can calculate the resistance based on the input voltage (1V) and the input current (which you can "measure" by hovering over the wires).

• That's an interesting tip and creative. However, knowing series and parallel shouldn't be considered trivial to the point where you need external tools or calculations. Someone who is well educated on the subject should be quick to tell you whether something is in parallel or series. Commented Aug 24 at 23:15
• Absolutely agree, this is more of a learning tip so that they can check their answers easily and maybe play around with the tool. Commented Aug 24 at 23:16
• I'll give you +1 because it technically is a solution that is testable, albeit slightly inconvenient 😊 Commented Aug 24 at 23:23

You'll see this type of circuit quite a bit in textbooks and electronics courses, the idea of them is to teach you to look at the circuit carefully. They intentionally draw the circuits in a misleading way, for instance they will do things like insert short circuits that you may miss if you are concentrating on the component values, add elements that have no effect on the result, and draw the circuit using an unconventional layout.

The best thing to do is to redraw the circuits to make them clearer. You also have to look at exactly what the question is asking. In these circuits they are asking for $$\R_T\$$, the resistance looking into the two terminals on the left, the terminals on the right don't really enter into it.

If you were to redraw the first circuit it might look something like this:

simulate this circuit – Schematic created using CircuitLab

Drawn like this the total resistance is pretty obvious.