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How does corrosion affect the resistivity of copper wire?

  1. May 10, 2015 #1
    • moved to homework forum; member warned to use h/w template in future posts
    I'm not sure if corrosion does have a significant effect on copper in general but if it does, how and why does it happen, and the process of it happening and its effect on the overall resistivity?

    This is for a physics assignment...Please help if you can.
    Thank you
     
  2. jcsd
  3. May 10, 2015 #2

    CWatters

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    Homework (or similar) should be in the homework section of the forum so this thread might get moved.

    What chemical reactions are you familiar with that involve copper? What can pure copper react with and what does it turn into? Do those reaction products conduct electricity? If not then the resulting wire will comprise less pure copper and more insulator than the original wire. That will change the overall resistivity.
     
  4. May 10, 2015 #3
    Thank you so much for answering. I didn't know the posting procedure as its my first time on here. Will remember next time..thanks
     
  5. May 10, 2015 #4

    Philip Wood

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    For a specimen of solid copper, the inside won't be exposed to the corroding agent(s). It is the (original) surface that will be corroded, though the corrosion will spread further and further into the metal. The corrosion would have to be very severe for none of the original metal to remain. For example, for a copper wire, it's the outer layers that would be corroded at first. There will be a huge increase in resistivity of the affected layers. Would you expect the uncorroded metal (if any remains) to suffer much change in resistivity?
     
  6. May 10, 2015 #5
    I don't think the uncovered materiel in the copper wire will differ in the resistivity factor but the overall resistivity might change since the resistance is inversely proportional to the cross sectional area of the wire and the resistance of the wire will increase as the area decreases.But then again I ain't no expert, kinda why i am on a physics forum :)

    Thanks anyway :)
     
  7. May 10, 2015 #6

    Philip Wood

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    I don't find the idea of overall resistivity (mean resistivity?) much help here. I'd have thought the corroded wire (if you're dealing with a wire) is better modelled as a cylinder of uncorroded copper metal (of smaller diameter than the original wire, but resistivity unaffected) in parallel with a 'sheath' of corrosion products of very high resistivity. I'd have thought, too, that the sheath's resistance would be so high compared to the resistance of the copper 'core', that the sheath can be forgotten about altogether when calculating the overall resistance.
     
  8. May 11, 2015 #7

    CWatters

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    +1 to that.

    The resistance of a wire depends on the cross-sectional area. It's fairly obvious that if you dissolve away the outside with acid then the cross sectional area reduces and the resistance increases. If the outside reacts with another chemical (Oxygen? Sulphur?) then you need to find out if the products of that reaction have a lower or higher resistivity. For most I think the resistivity will be so high that it can be ignored. If not then model it as two "wires" in parallel.
     
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