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Calculating combined resistance of wires

  1. May 21, 2015 #1
    1. The problem statement, all variables and given/known data

    upload_2015-5-22_8-19-31.png
    2. Relevant equations
    • R ∝ 1/A

    3. The attempt at a solution
    Since there are six copper wires and a steel core, I added the resistance of all the wires and the core and divided them by 7, though I don't think my approach is right since the resistance of the copper and steel wires are different. As such my answer is about 22.9Ω, which is wrong. The answer is B, 1.6Ω, which is just the quotient of the the total resistance of the six copper wires. Why is the resistance of steel core not taken into account in this case?
     

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  3. May 21, 2015 #2

    haruspex

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    Do you know how to calculate the net resistance of resistors in parallel?
     
  4. May 21, 2015 #3
    Ermm...yes. But why is the steel not taken into account?
     
  5. May 21, 2015 #4

    haruspex

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    Why are you so sure it isn't? Have you done the calculation taking the steel into account?
     
  6. May 21, 2015 #5
    Oh, so is the working 6(1/10) + 1/100 correct for 1/R?
     
  7. May 21, 2015 #6

    haruspex

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    Yes.
     
  8. May 21, 2015 #7
    Thanks. So is this combined resistance of six different copper wires and steel less than a power cable just made up of one copper wire of the same cross-sectional area?
     
  9. May 21, 2015 #8

    haruspex

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    What do you think?
     
  10. May 21, 2015 #9
    I think the resistance of six different copper wires and the steel would be lesser. However if it's just the six copper wires without the steel, then they would be the same.
     
  11. May 21, 2015 #10

    haruspex

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    Quite so.
     
  12. May 21, 2015 #11
    Why quite so? Is it not really correct?:smile:
     
  13. May 21, 2015 #12

    haruspex

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    "Quite so" means, yes, that is exactly correct. (British English idiom?)
     
  14. May 21, 2015 #13
    Oh I see.
     
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