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Resistance in Parallel Equation

  1. Jan 16, 2016 #1
    The formula to find the total resistance in a parallel circuit is 1/R=1/R1+1/R2+1/R3, but wouldn't it be easier to use R=1/(1/R1+1/R2+1/R3)? I've only ever seen the equation written like that once before, and I'm wondering if there's a reason as to why it's never really used?
  2. jcsd
  3. Jan 16, 2016 #2


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    What's easier to use depends on what you have and where you want to go.
    The 1/R expression is easier to understand and to remember:

    Voltage is the same for all R
    Total current = Voltage / Total resistance
    Total current = Sum of individual currents = Sum ( Voltage / Individual resistance i )​

    Divide by Voltage and you get the 1/R = Sum (1/Ri )
  4. Jan 16, 2016 #3


    Staff: Mentor

    It is USED plenty. Students are expected to be able to divide easily.

    Similarly, Newton's 2nd law is almost always written F=ma, even though students are expected to recognize and use the equivalent a=F/m and m=F/a.
  5. Jan 16, 2016 #4
    Thanks! I suppose it does make sense that we don't write it that way.
  6. Jan 18, 2016 #5


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    What others said. The two equations are mathematically the same. If anything the second form of the equation is used more frequently.
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