Basic equivalent resistance problem

Discussion in 'Homework Help' started by fdsa, Jun 28, 2012.

  1. fdsa

    Thread Starter New Member

    Aug 16, 2011
    9
    0
    Let:
    R1 = 18\Omega\\R_2 = 12\Omega\\R_3 = 9 \Omega\\R_4 = 6\Omega\\

    If I assume R_1 & R_2 are in series and R_{12} in parallel with R_{34} the equivalent resistance is correct but I have no solid reasoning behind this conclusion. As I see it the current in the top node connecting R_1 & R_2 has two paths to choose from?

    [​IMG]
     
  2. daviddeakin

    Active Member

    Aug 6, 2009
    207
    27
    Perhaps it will be more clear if you redraw the circuit like this:
    [​IMG]
     
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  3. fdsa

    Thread Starter New Member

    Aug 16, 2011
    9
    0
    Thank you, probably need to get more exercise reducing those slightly more complicated resistance problems but that made it completely clear.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,716
    4,788
    Never be afraid to resketch a circuit in a configuration that makes more sense to you. The human brain is very good at pattern recognition, but that works against us when we see a new pattern that is really just a redrawing of a different pattern -- our brain insists that it is a new pattern with no relationship to previous patterns and we tend to accept it. But as we redraw a circuit, that same tendency biases us toward using patterns with which we are already familiar, enabling us to see them.
     
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