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Find the resistance of a wire (conductor)

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  1. Jan 21, 2016 #1
    1. The problem statement, all variables and given/known data
    If the diameter of a wire (conductor) is dimidiated , then its resistance:
    A Remains unchangable
    B is diminiated
    C Becomes two times greater
    D Becomes 4 times greater

    2. Relevant equations
    R=constant*length/Surface

    3. The attempt at a solution
    Cross sectional area=pi r^2=pi (D/2)^2=piD^2/4
    Then the resistance becomes 4 times greater.
    But in my book the answer is C.
     
    Last edited: Jan 21, 2016
  2. jcsd
  3. Jan 21, 2016 #2
    Is the surface area really proportional to r^2?
     
  4. Jan 21, 2016 #3
    I think it is. Only if you consider pi to affect that
     
  5. Jan 21, 2016 #4
    Are you confusing surface area and cross sectional area?
     
  6. Jan 21, 2016 #5
    Can you tell me the difference. in my book it says Resistance is in disproportional to the cross section of the resistance.
     
  7. Jan 21, 2016 #6

    cnh1995

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    Surface area means area of the entire surface of the conductor. Cross sectional area is the area "through" which the current flows. Resistance is inversely proportional to the cross sectional area of the conductor.
     
  8. Jan 21, 2016 #7
    I understand. But how can this affect the solution of my exercise?
     
  9. Jan 21, 2016 #8

    haruspex

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    If "dimidiated" means halved, I agree that the answer is D.
     
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