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Adding up resistors

  1. Feb 10, 2010 #1
    1. The problem statement, all variables and given/known data


    i'm a noob, and i am having trouble adding resistors. this circuit can be reduced to 1 resistor. what is its value?

    2. Relevant equations
    parallel: 1/Rtot=1/R1+1/R2+1/R3+1/R4
    series: Rtot=R1+R2+R3+R4

    3. The attempt at a solution
    so i thought 3, 2, 2 added up in series and you just do 6/8+1/4, but this isn't right. =/ i'm having trouble discerning which resistors are parallel and which are in series. any help would be appreciated.
  2. jcsd
  3. Feb 10, 2010 #2
    2 resistors R1 and R2 are in series if one connector of R1 is connected to a connector of R2 and nothing else is connected to these connectors. (or if you can determine that no current can flow through such a connection)

    None of the resistors here is in series with any other.
    The 3 ohm resistance isn't in series with any of the 2 ohm resistances because the point between the 3 ohm resistance and any of the 2 ohm resistances is also connected to the other 2 ohm resistance

    2 resistors are parallels if one connector of R1 is connected to a connector of R2 and the other connector of R1 is connected to the other connector of R2. There's only 1 pair of
    resistances here thats parallel.

    The direction they are drawn in doesn't matter.

    Once you combined those resistances, you can look again for a pair of resistances that is in series or parallel.
  4. Feb 10, 2010 #3
    huh? so are you saying i can disregard the 3 Ohm resistor?
    i know the answer is supposed to be 2. i don't know how to get there though.
  5. Feb 10, 2010 #4
    No. I said the 3 ohm resitor isn't in series with any of the 2 ohm resistances. What you have to do is find the pair of resistances that's parallel, combine those and then look for other series of parallel pairs
  6. Feb 10, 2010 #5
    is 3 parallel with 4 and 2 is parallel with 2?
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