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Homework Help: Electrical circuts

  1. Apr 2, 2005 #1
    Maybe I'm too tired, but this has been driving me nuts and I can't find an answer in the books (i own a few of my own).

    How do you find the current if there are both series and parallel resistors? I can't figure it out and it's been driving me crazy.
  2. jcsd
  3. Apr 2, 2005 #2
    Find the equivalent resistance of the resistors in parallel and then use that in series with the others? It'd be easier to explain if you had a specific problem to do.
  4. Apr 2, 2005 #3


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    Science Advisor

    Try the following Web Site. It presents step-by-step instructions for reducing complicated series/parallel combo circuits. Moreover, once the "Equivalent Resistance" is determined, it shows how to work backwards to reconstruct the original circuit for evaluating currents and voltage drops across the original resistors.
    -----> http://members.aol.com/_ht_a/RAdelkopf/parallel.html [Broken]

    Last edited by a moderator: May 2, 2017
  5. Apr 2, 2005 #4
    Or if the circuit is too complex for reduction you can use node voltage or mesh analysis to find the voltage drop and current. Then you could use Thevenin's(or Norton’s) theorem to find the input or output resistance.
  6. Apr 2, 2005 #5


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    Gold Member

    Nylex has the answer. Reduce the parallels to series, then do the series.
  7. Apr 2, 2005 #6
    Why is Nylex the one with the right answer? Why is it parallel then series? Take the case of R1 in parallel with the series of resistors R2, R3. I could right
    R1//(R2+R3) /*parallel first*/
    R4 = R2 +R3 /*series reduction*/

    But really in R1//(R2+R3) you have already put R2 and R3 in series so in this case it would be series then parallel.

    Series then parallel or parallel then series it makes no difference. This method will not work for circuits with components which are neither in parallel or series.(often confused with components in series and parallel) On the other hand Thevenin's or Norton’s theorem will work for any circuit.
  8. Apr 3, 2005 #7
    I used Thevenin's theorum and it worked.

  9. Apr 3, 2005 #8
    Glad I could help, it is al ways nice to get a confirmation. Since this is your second post welcome to the forum.
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