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Resistance and the length of the wire

  1. Sep 24, 2014 #1
    Hi!
    The question is simple, seemingly...

    Doubling the length of a wire, doubles the resistance of the wire...

    Why?

    There is one interesting point to it:

    Doubling the length of the wire also makes the ELECTRIC FIELD weaker TWO times.
    That automatically makes the current smaller two times....

    We know that making the resistance bigger 2 times, makes the current smaller 2 times.

    I see a parallel here! It seems that resistance is NOT necessarily a property of the matter itself, rather it is the combination of factors that make the current smaller than it would be if there were no such factor present (e.g making the wire longer). So it seems to me that the "resistive factor" here is the weakening of the electric field...

    Any opinions?

    Kind regards!
     
  2. jcsd
  3. Sep 24, 2014 #2
    The electric field is due to the current flowing through the wire, not the resistance of the wire.
     
  4. Sep 24, 2014 #3
    I assure you that this is not true!
    The electric field in the wire is due to the surface charge gradient ON the conductor. The surface charge gradient is caused by the battery! Electric field CAUSES the current, not vice versa!
     
  5. Sep 24, 2014 #4
    Ott: what is your logic if instead of doubling the length of the wire, you double the cross sectional area of a cylindrical wire?
     
  6. Sep 24, 2014 #5
    You are blinding me by science, as the song goes, but I think I might see what you are saying.
    Resistivity is tabulated for materials, but to obtain a value, one has had to previously measure the voltage and current through a section of the material.
    Hmm.
    Then it is back to a catch-22 situation, or chicken and egg question of which determines which - ie voltage, current, resistance.

    What about what qsal has mentioned?
     
  7. Sep 24, 2014 #6
    Doubling the cross sectional area doubles the number of charge carriers per area, which in turn directly doubles the current. It is a condition, by which the current is able to be twice as high compering to the situation where the wire is thinner: therefore we can again, say that the resistance to the current is less.
     
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