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Aluminium vs Copper in power lines

  1. Jun 7, 2016 #1
    Hi,

    I have a question concerning the use of aluminium in power lines. I know that it's lighter than copper and thus cheaper, which is the main reason we prefer it above copper. But in fact alumunium has a lower conductivity than copper. Why is it then that one kg of aluminium can carry twice as much electricity as one kg of copper ? This seems to be contradictory to me.

    Thank you :)
     
  2. jcsd
  3. Jun 7, 2016 #2

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    Here's some information that should be useful in the process of considering the question objectively:

    Resistivity, [itex] \rho_e, \mathrm{(\Omega \cdot m)} [/itex]:
    Copper: [itex] 1.68 \times 10^{-8} [/itex]
    Aluminum: [itex] 2.86 \times 10^{-8} [/itex]​

    Conductivity, [itex] \sigma, \mathrm{(S / m)} [/itex]:
    Copper: [itex] 5.96 \times 10^{7} [/itex]
    Aluminum: [itex] 3.50 \times 10^{7} [/itex]​

    Density [itex] \rho_m, \mathrm{(g/cm^3)} [/itex] [Edit: corrected copy-paste error and a typo.]
    Copper: 8.96
    Aluminum: 2.70
    By the way, resistivity and conductivity are not independent. They are merely reciprocals. [itex] \rho_e = 1/\sigma [/itex]. Both resisitivity and conductivity are given in terms of spacial dimensions, such as unit cross-sectional area and unit length.

    If [itex] A [/itex] is the cross sectional area of the conductor, [itex] \ell [/itex] is the conductor's length, then

    Resistance, [itex] r = \frac{\rho_e \ell}{A} [/itex]

    Conductance, [itex] G = \frac{1}{r} = \frac{\sigma A}{\ell} [/itex]

    Mass, [itex] m = A \ell \rho_m[/itex]
     
    Last edited: Jun 8, 2016
  4. Jun 7, 2016 #3

    rbelli1

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    You got those swapped. Copper is the higher density material.

    BoB
     
  5. Jun 7, 2016 #4

    Nidum

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    Think about two wires of equal length . One made from 1 kg of Copper and the other from 1 kg of Aluminium .
     
  6. Jun 7, 2016 #5

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    And the price of metals depends on many factors besides just their densities (their weights). Lead is not cheaper than silver because it is lighter (it isn't: lead is heavier than silver); it's cheaper because it is more abundant and easier to extract.
     
  7. Jun 7, 2016 #6

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    Thanks. It was a copy-paste error. Correction made.
     
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