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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

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  • \$\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
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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.

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  • \$\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
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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 .

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  • \$\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

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