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Electric field distribution in a conductor with moving charges

  1. Jun 10, 2009 #1
    I'm trying to reconcile some concepts in electrostatics and dynamics to do with electric fields in conductors.

    The relative permittivity (constant) of a material seems to be determined by it's ability to be polarized and subsequently induce an electric field within a conductor or dielectric. The permittivity (constant) of a vacuum seems to merely facilitate the calculation of the electric field (voltage) at some distance from a charge or group of charges.

    When looking at the electric field in a vacuum some distance from point charge/s, there doesn't seem to be any sort of attenuative effect other than the electric field strength diminshing due to the distance from the point charge (characterised by a the ubiquitous steradian 1/(4[tex]\pi[/tex]r2) function).

    I guess the implication here is that lower permittivity constants in dielectrics and insulators result in the speed of electromagnetic wave propagation through these media being lower than the speed of light.

    The implication here is that the electric field can propagate through any medium in the absence of motion of charge carriers. This seems counterintuitive though.

    Imagine for instance a voltage source (say a bunch of static charges) connected to a strong dielectric (so that the charge cannot spread along the wire) and a long wire. Can you measure the voltage at the end of this wire using a device with an infinite input impedance? I would have thought that you need a small amount of charge to flow into the measuring device to be able to ascertain the electric field at the end of the wire.

    Conventional circuit theory would tell you that the voltage at the end of the wire is the same as the voltage at the start of the wire in the absence of moving charges. However, if you consider the attenuation of the electic field due to permittivity considerations, one would expect the voltage at the end of the wire to be lower as the electric field is attenuated by the conductor.

    I'm struggling to find an intuitive explantion of how potential distributes itself in media other than a vacuum. What does it mean to say that the potential drops across a circuit loop proportionally based on the current flowing and resistance of the loop?

    How are charge carriers imbued with potential that they can shed through collisional processes whilst drifting through a conductor? Assuming that the charge carriers themselves have potential that can be lost seems incongruent with the conductor having an electric field distribution through it based on it's permittivity.
     
  2. jcsd
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