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Homework Help: Archived Coaxial Cable With Potential Difference between conductors

  1. Mar 5, 2013 #1
    1. A coaxial cable is powering a light bulb with a steady flow of current (DC current). The electric potential difference between the outer and the inner conductor of the cable is delta V and the current flowing in the cable is I. The inner conductor's outer radius is a and the outer conductor's inner radius is b.

    Given that the higher electric potential is at the outer conductor, in which direction is the current in the inner conductor flowing, towards the light bulb or away from it?

    2. Maxwell's Equations

    ∫ Eds = -d∅/dt

    ∫Bds = μI + εμ d∅/dt

    3. I believe the current in the inner conductor is flowing away from the light bulb. I think the current travels from the outer conductor to the light bulb to light it. Then after, it goes through the inner conductor.

    The problems I have with my thinking is how can there be this continuous loop. I know that because there is a potential difference between the outer shell and inner shell (E-Field points radially inward) and I know that it would make sense for current to flow from the positive (higher electric potential) to the negative (lower electric potential), but I don't think my logic is correct.

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 13, 2017 #2


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    Science Advisor
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    Gold Member

    The OP is correct. Conventional current flow is from the outer (+ve) through the bulb to the inner (-ve). So it would be towards the bulb in the outer and away from the bulb in the inner.

    The problem statement says the current is DC so the dimensions of the cable are irrelevant.
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