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I Electrical energy transmission is on the inside or outside of a conductor

  1. Sep 11, 2018 #1
    Hi,
    Is it true that the transmission of energy is not inside an electrical conductor, but outside the metal. this even for frequencies around 50 hertz.
    Thank's
     
  2. jcsd
  3. Sep 11, 2018 #2

    anorlunda

    Staff: Mentor

    Yes, see https://en.wikipedia.org/wiki/Poynting_vector

    However, we teach that to students who are studying Maxwell's Equations. We do not mention it to students studying circuit analysis, because it makes no difference at that level and it would only serve to confuse.
     
  4. Sep 11, 2018 #3

    marcusl

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    Untrue. The skin depth in copper is about 3 cm at 50Hz, so electric current is carried throughout the cross section of any typical wire.
     
  5. Sep 11, 2018 #4

    anorlunda

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    He didn't ask about the current, but rather the energy. Read the Wikipedia article.
     
  6. Sep 11, 2018 #5
    Thank you anorlunda for your very clear explanation, that's why the quality of the dielectric in a coaxial cable, support for high frequency energy, is very important. Moreover, under your control, at ultra high frequency, several Ghz, the central conductor become unnecessary, it is called in this case the waveguide
     
  7. Sep 11, 2018 #6

    marcusl

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    Sorry, my mistake.
     
  8. Sep 12, 2018 #7

    davenn

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    yes indeed, because the energy is transmitted in the electric field around the conductor. and that is why the type of dielectric is important.
    Very low loss coax cables use as little amount of solid dielectric as possible. Many use a thin Teflon spiral which its main purpose is to
    keep the centre conductor and the outer conductor from touching each other. Most of the dielectric is air.

    Air-Dielectric-Coax-Cross-Section-e1463494709155.jpg

    low_loss_coax.jpg



    Yup, so then you only have the outer shield which constrains the electric and magnetic fields

    dJQW1.png



    cheers
    Dave
     
  9. Sep 12, 2018 #8

    sophiecentaur

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    This question appears to be very harmless and deserving a simple answer. But the fact is that, in there is the dreaded "what actually happens?" question - to which there is never an answer.
    You can treat most circuit problems without needing to decide one way or another. You can usually treat wave / antenna / transmission line problems by assuming that the power is not transmitted through the metal bits. But the losses inside the conductors that 'guide' the power can become relevant and those losses can be described in terms of power actually flowing through the conductor / wire / waveguide walls.
    The only explanation for the fact that medium and low frequency Radio Waves 'hug' the ground and don't go off into the sky is that the losses in the ground cause the waves to tilt downwards towards the ground. No resistance, no wave tilt and the ground signal dies out.

    As with all of Science and Engineering, we describe things by using models that work. That's all. Nothing in Science is Really REAL.
     
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