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General Formula Resistors Polyhedron

  1. Oct 24, 2011 #1
    Hello all,

    Does anyone know of any general formula for the equivalent resistance between two opposite points of a regular polyhedron (cube, dodecahedron ..) with all the resistors equal to R?
     
  2. jcsd
  3. Oct 25, 2011 #2
    draw a graph of the polyhedron. choose an arbitrary point as one of the terminals. Now mark all points that are 1 resistance away from this, then all points that are at distance 2, etc.
    you should get 1 point at maximum distance, wich is the other terminal.
    (this won't work for a tetrahedron, because there is no opposite point)

    All points at the same distance, will have the same voltage, because of symmetry, so you can connect them with wires. The resulting network can easily be solved by replacing series and paralles resistances, because all resistances from an n to an n+1 distance point will now be parallel

    for a dodecaedron, I get

    3 points at distance 1
    6 points at distance 2
    6 points at distance 3
    3 ponts at distance 4
    1 point at distance 5

    3 resistances between distance 0 and distance 1 points
    6 resistances between distance 1 and distance 2 points
    6 resistances between distance 2 and distance 3 points
    6 resistances between distance 3 and distance 4 points
    3 resistances between distance 4 and distance 5 points

    6 resistances between points of equal distance, wich will carry no current

    so the total resistance is (1/3+1/6+1/6+1/6+1/3)R = (7/6)R
     
  4. Oct 25, 2011 #3

    Bill_K

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    Science Advisor

    Careful, I once drew an infraction for answering the cube problem, on the grounds it was "homework"! :rofl:
     
  5. Oct 25, 2011 #4
    Thanks, but do you know a general formula ?
     
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