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Homework Help: Coefficient of resistivity

  1. Sep 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A wire, 50.0 m long and 2.00 mm in diameter is connected to a source with a potential difference of 9.11 V, and the current is found to be 23.45 A. Assume a temperature of 20°C and using Table 17.1, identify the metal out of which the wire is made of.

    2. Relevant equations


    where R is the resistance p is the coefficient of resistivity, l is the length and A is the area

    3. The attempt at a solution

    ok since we are solving for p first i found R by the equation V=IR and found R to be .388
    next i found the area using the surface area of a cylinder and found that to be .628
    next i divided length by .628 and found that to be 79.618
    so then i divided .388/79.618 and got 4.8*10^-3
    thats the right magnitude but it does match any of my options coefficients.

    the problem lets me choose whether the metal is gold, silver, copper, or iron.
  2. jcsd
  3. Sep 20, 2008 #2


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    Homework Helper

    wrong area. you want the cross-sectional area of the wire

  4. Sep 20, 2008 #3
    ugh ok i got the area by .002*.002*3.14 = .00001256
    then i divided 50/.00001256 and got 3980891.72
    so then i divided my R .388 by 3980891.72 an got 9.74e-8
    not right...
  5. Sep 20, 2008 #4
    plz help i really dont understand why this is still wrong...
  6. Sep 20, 2008 #5


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    Homework Helper

    you still have the wrong number for the area. The *diameter* is 0.002. The *radius* is 0.001.
    You used Area=diameter*diameter*Pi, which is wrong.

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