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Homework Help: Resistance per unit length

  1. Aug 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Some electrical appliances are used with long cables to connect to them to the electrical supply. State and explain 2 reasons why these cables should have a low resistance per unit length.

    3. The attempt at a solution

    well for the long cables, a low resistance per unit length would mean a low resistance for the cable itself. a larger current will flow.

    i cannot see any advantage in that. rather the cables will be less safe with a larger current. the power dissipated, I2R, will be larger, hence less efficient.

    so i don't know....
  2. jcsd
  3. Aug 27, 2008 #2


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    Hi Kushal! :smile:

    No … you've completely ignored the resistance of the appliance

    it is (mostly) that resistance which determines the current, I.

    So the current is more-or-less fixed by the appliance.

    So the effect of the resistance of the wire is … ? :smile:
  4. Aug 27, 2008 #3
    yeah you're right, i completely ignored that. a small current might not be able to operate the appliance.

    errmm i still can't find the second reason.... a hint would be great...lol

  5. Aug 27, 2008 #4


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    It looks like you were on to the second drawback in your first try.
  6. Aug 27, 2008 #5
    EDIT: Nevermind, got resistance confused with impedance.

    Anyway, yes you were close. Think of the Thevenin equivalence circuit.
    Last edited: Aug 27, 2008
  7. Aug 4, 2011 #6
    You guys have completely forgot that the higher the voltage of the current moving through the mains power the less energy that is lost through heat and for that to work the resistance must be low.
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