1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    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!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook