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R Network- finding total resistance.

  1. Apr 26, 2009 #1
    1. The problem statement, all variables and given/known data
    Assuming R = R' = 1.97 Ω in the network shown above, determine the net resistance

    a) between the points a and c
    b) between points a and b.
    HELP: Use symmetry.
    HELP: Imagine applying a voltage between a and c and think about what current will flow in each resistor.

    https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/Knox/phys130a/spring/homework/09/02/P26_36.jpg [Broken]


    2. Relevant equations
    Series: Rtotal=R1+R2
    Parallel: Rtotal=(R1-1+R2-1)-1


    3. The attempt at a solution

    Well, I redrew the series in my notebook as parallel and series, but in both attempts at a re-draw, I ended up with a weird branch that wasn't really either series or parallel, because of how it connected. I tried solving it anyway (and have come up with 1.313 for the resistance between a and c) but nothing's been right. I'm just not sure what to do with the weird branch. :/
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 26, 2009 #2

    LowlyPion

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    Homework Helper

    Observe that with all the resistors equal to each other that you can drop out the R' resistors that cross between the || branches. At each leg of your || you have a voltage divider with no net voltage across the R'. This should make your calculation a bit easier.

    For instance between AC:

    1/R + 1/2R + 1/2R = 1/Rac
     
  4. Apr 26, 2009 #3
    Oh wow, that makes things a lot simpler. I wasn't aware that I could drop out that resistor. Thank you!
     
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