enter image description here

I have these two series and parallel circuits and I want to know how I should find the voltage through R1, R2, R3 and R4. I know I should use the rules of voltage divider but I don't know how when I have resistor (R5) in the way and also in figure 1 there is a wire between for the current to go through.

How I should get the voltage through voltage divider in figure 1 and how the voltage changes for R1, R2, R3 and R4 in figure 2 (when the wire for current isn't there anymore).

R1 = R4 = 1k ohm R2 = R3 = 100 ohm R5 = 10 ohm E = 5 V

  • \$\begingroup\$ Voltage is across, current is through. \$\endgroup\$ – Olin Lathrop Apr 3 '16 at 13:01
  • \$\begingroup\$ This is a pretty textbook problem for Y-Delta transforms. \$\endgroup\$ – Matt Young Apr 3 '16 at 13:22

We don't give complete answers to homework here.

However, consider in the left circuit that R1 and R3 are in parallel, and R2,R4 are in parallel. In the right circuit, R1+R2 is in parallel with R3+R4.

Given these observations, it should be easy to find the voltages everywhere, which is a start on finding the currents.

That's one way to solve this. There are several equivalent ways.

| improve this answer | |
  • \$\begingroup\$ Thanks for answering so fast. Ok I have understood know that in the right circuit R1 and R3 are in parallel and that R2 and R4 are in parallel. I also understand know that R1+R2 is in parallel with R3+R4. So what really makes it hard for me to understand is R5, I don't really know what to do with it... And I would like to know if I should calculate the total resistance and find out the voltage or if I should use voltage divider. I been watching some youtube clips where they state that you could use the rule for voltage divider if the resistors are is series with each other. \$\endgroup\$ – Vetenskap Apr 3 '16 at 13:31
  • \$\begingroup\$ I have just started this course, and would like some guidelines on how to solve such complex circuits. I understand that you don't give complete answers, but I would appreciate it if you could try to explain a little more in detail if that is okay. :) \$\endgroup\$ – Vetenskap Apr 3 '16 at 13:31

In a series circuit ,the voltage across the circuit is the sum of the voltages across each component. In a parallel circuit, the voltage across each of the components is the same.

For left figure : R1//R3 => same voltage across R2//R4 => same voltage across

Now use voltage divider rule (apply for resistors in series)

You have R5 in series with (R1//R3) and with (R2//R4)

For right figure you have R5 in series with [(R1+R2)//(R3+R4)], use voltage divider rule to find V across [(R1+R2)//(R3+R4)]

(R1+R2)//(R3+R4) , therefore voltage across R1+ R2 are same as R3+R4, find this voltage V, then use voltage divider rule again .

| improve this answer | |
  • \$\begingroup\$ I have calculated all the way for R5 in series with [(R1+R2)//(R3+R4)] and I found the voltage, but from there I don't really understand how I should find voltage for R1+R2 and R3+R4 separately? \$\endgroup\$ – Vetenskap Apr 3 '16 at 15:17
  • \$\begingroup\$ If you found voltage across R1+R2 , if R1//R2 then V is same for them. \$\endgroup\$ – Tim Apr 3 '16 at 15:48
  • \$\begingroup\$ If R1 in series with R2, use voltage divider rule one more from the V you found \$\endgroup\$ – Tim Apr 3 '16 at 15:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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