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Effective Resistance if bent in the form a circle

  1. Dec 9, 2011 #1
    1. The problem statement, all variables and given/known data

    A wire of resistance 8R is bent in the form of a circle. What is the effective resistance between the ends of a diameter AB?


    2. Relevant equations
    I have attached the image and my attempt to solve it as told by my teacher.


    2. Relevant equations



    3. The attempt at a solution
    But I dont know why the reciprocal formula is used. Please help.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

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  2. jcsd
  3. Dec 9, 2011 #2
    It's because it is equivalent to having two resistors in parallel.
    The current entering at A has a choice of 2 directions.
    Both involve taking a path that is 4R. That is, half the resistance of the complete wire. (Round half the circumference to B.)
    So to find the combined resistance, you need to add 4R and 4R in parallel.
     
  4. Dec 24, 2011 #3
    Thanks a lot stonebridge. Your help is very much appreciated
     
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