I have this circuit and I need to find an equivalent resistance. I am very confused by the shape of the circuit because it appears like a more complex problem than I think it should be.

Ultimately, I think this is simply a series of 3 resistors and the total resistance should be 3R. Is this correct or do the extra wires matter? enter image description here

  • $\begingroup$ Hint: you can move everything around as long as you keep the topology the same. Try placing all points of the same voltage as $A$ at the top, and all points of the same voltage as $B$ at the bottom. $\endgroup$
    – knzhou
    Apr 17, 2017 at 4:33
  • $\begingroup$ I gave wrong answer. I deleted it to avoid confusion. I agree it is R/3 now instead of R/2. $\endgroup$
    – hywong
    Apr 17, 2017 at 5:01
  • $\begingroup$ I suppose the first resistor has the same voltage as A and the third resistor has the same voltage as B but I don't understand how this shows it's parallel. $\endgroup$
    – M123
    Apr 17, 2017 at 5:15

3 Answers 3


the answer should be R/3, the resistances are in parallel. you need to modify the circuit a little bit.

  • $\begingroup$ Correct! I had just drawn that parallel circuit when your answer popped up. $\endgroup$
    – K7PEH
    Apr 17, 2017 at 4:39
  • $\begingroup$ I really can't figure out how this can be rearranged into a parallel circuit. What's the first step? $\endgroup$
    – M123
    Apr 17, 2017 at 5:18
  • $\begingroup$ @M123 I've uploaded a picture in gdrive: link . Hope it helps. $\endgroup$ Apr 17, 2017 at 5:36

Req = 1/(1/R + 1/R + 1/R) = 1 /3/R = R/3

The point after two R is A, and the point between two R is B. So just flip those points to make a single point of A and B, respectively. Then, you will see that the resistances are all in parallel. Thus, the total equivalent resistance is R/3.

  • $\begingroup$ If you vote down this answer that means you don't understand it well. $\endgroup$
    – Pisiko
    Apr 17, 2017 at 5:48

The extra wires absolutely do matter. There is a wire that shorts the first two resistors, meaning that there really is only one resistor in the circuit. So, the effective resistance is R.


Not the answer you're looking for? Browse other questions tagged or ask your own question.