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Homework Help: Finding length and diameter of copper wire!

  1. Feb 16, 2010 #1
    Suppose you wish to fabricate a uniform wire out of 1.0 g of copper (Density of copper is 8.93 x 10^3 kg/m^3). If the wire is to have a resistance of R = .5 ohms, and all the copper is to be used, what will

    a) the length and
    b) the diameter of this wire?

    this has me tottally confuzed because i can not put together a formula to find lenght or the diameter of the wire. Help?
  2. jcsd
  3. Feb 16, 2010 #2
    You can compute the volume of the wire from the mass and the density.

    If you know the diameter is equal to d, you can compute the length of the wire (from the equation for the volume of a cylinder)

    If you know the length and the diameter, you can compute the resistance (resistivity of copper is [itex] 1.72 \cdot 10^{-8} \Omega m [/itex] )

    The resistance will be a function of the chosen diameter d. Set this equal to 0.5 and you can find d
  4. Feb 18, 2010 #3
    ok thank you.

    so if i have a volume of 1.12 x 10^-4, and the equation for volume of a cylinder is (pi)(h)(r^2), i dont get how to computer the length if i do not have a height or a radius? and then i need the length and diameter to get resistance (given at 0.5), how do i get this into finding the diameter?

    i am confuzed on what formula to use or how do use volume of a cylinder to get d??
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