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Equivalent resistance in a complex circuit

  1. Mar 10, 2015 #1
    1. The problem statement, all variables and given/known data

    1. In the circuit shown, R1 = 0.810 Ω, R2 = 8.10 Ω, R3 = 81.0 Ω, and R0 = 810 Ω.
      See attachment

    1. Calculate the equivalent resistance of the circuit when a 7.70 V power supply is connected between points A and C.
      Calculate the current through R0 and R1
    2. Relevant equations
    Series: resistances sum
    Parallel: 1/Req=1/R1+1/R2...
    3. The attempt at a solution
    Okay so I'm not really understanding circuits well. From what I would gather R3 and R0 would be in series, but I'm just really confused about R1 and R2. And I'm not even 100% sure if R3 and R0 are actually in series since it branches off to D between them as well..

    Attached Files:

  2. jcsd
  3. Mar 11, 2015 #2
    You're correct that R3 and R0 are in series. Now combine them and notice what happens with the circuit.

    Now, why doesn't it matter that D is in between them? Because in this particular scenario, the D branch is an open circuit, so there will be no current flow in it, so you can treat the circuit as if thst branch isn't even there.

    So if the B branch is also an open circuit, then...
  4. Mar 11, 2015 #3


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    Staff: Mentor

    I think you should redraw the circuit, leaving off what is irrelevant, including a piece of wire going nowhere and labelled D. Then see what you have.
  5. Mar 11, 2015 #4
    Thank you guys! I found R0 and R3 are in series with each other, and so are R1 and R2, and these two series are in parallel with each other. I managed to calculate Req, and the current through R0, but now I'm having trouble calculating the current through R1..I now that parallel resistors are supposed to have the same change in voltage across resistors, but I'm not really sure how to apply that here. I thought that the voltage change would be 7.7, and just divided that by R1 for the current, but that was wrong.
  6. Mar 11, 2015 #5
    Figured it out guys! Thanks for the help! Couldn't find an edit button so sorry for the double post just didn't want to unnecessarily take up more of anyones time than needed.
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