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Electricity through wires

  1. Apr 15, 2007 #1
    Is is known exactly how electrons flow through wires? For example a wire is conductive, the air around it is not, and thin wires conduct worse then thick wires, would this mean that the electrons force, or flow is greatest in the centre of the wire? Like water through a pipe?
  2. jcsd
  3. Apr 15, 2007 #2
    Yes it is very well known. I give you a very short and simplified (but correct) explanation:

    In a metal, there are so called "free electrons". There are electrons detached from the atoms (less than one for each atom) that can wander freely in the metal. But, as people in a room, they distribute more or less uniformly over al the room (metal).
    All the time there are collisions between the electrons and between the electrons and the atoms. There is equilibrium in the speed of electrons and the agitation of atoms. You said that electrons and atoms are in thermal equilibrium. That is they are at the same temperature.
    When you apply a voltage across the metal an electrical field appears and this electrical field pushes the electrons to the positive end. This push changes slightly the speed of electrons in the good direction. As the electrons gain speed they gain temperature and in the chocks with atoms they loss temperature and heat the atoms.
    This is the resistance: the electrons lose the gained energy, giving it to the atoms. To have a current, you must provide an electric field, plus energy and this energy heats the metal.
    Thin wire conduct worse than thick ones not of friction with the surface of the wire, as do water in a pipe. In a thin wire there are fewer electrons and to obtain the same current you must give them more speed. This asks for bigger electric field and gives bigger loses (heat).
  4. Apr 16, 2007 #3
    It might also be mentioned that electrons repel each other, causing a "skin-effect" to occur with respect to electron distribution in a live conductor.
  5. Apr 17, 2007 #4
    When giving an explanation it is better to avoid mentioning irrelevant subjects.
    Electrons do repel each other (I said " But, as people in a room, they distribute more or less uniformly over all the room (metal).").
    Anyhow, as electrons move in a sea of fixed positive charges (atoms which have lose an electron), essentially, they do not "see" the others electrons.
    Then repulsion between electrons is mostly irrelevant to metallic conduction.
    The "skin effect" has nothing to do with electron repulsion. It is due to magnetic forces exerted on moving electrons by the magnetic field created by the current. It is only relevant for alternating currents and at frequencies bigger than 1 or 2 tens of kilohertz.
  6. Apr 17, 2007 #5
    Ok, so they flow through a typical wire evenly spread out, from centre to outside?

    What happens when the wire is curved? Does the Tesla coil Lower amps, and raise voltage?
  7. Apr 18, 2007 #6

    The current "takes the bend" and more electrons pass at the side of the wire near the center of curvature than at the opposite outer side. The dependence is of the type 1/R, where R is the radius of the trajectory.

    Tesla coil is just a transformer. But the Tesla coils that you see in labs and technical museums
    work at high frequencies (20 -50 kHz), and have very high transformation ratios. They output tens of thousand of volts that are no very dangerous because of the "skin effect" at these frequencies.
  8. Apr 18, 2007 #7
    do you know if any changes happening in the electron orbitals of the wire's atoms? does a coil of Iron wire have more magnetic pull, and eddy force then a coil of copper wire? Since if you put an iron rod in a copper coil it's more magnetic then the copper coil alone.
  9. Apr 18, 2007 #8


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    There is a "skin" effect with high frequency AC.
  10. Apr 18, 2007 #9
    Indeed, in Chemistry and even in Physics it's well known. However, the Chemistry model in Quantum Mechanics really explains it well.

    Water is an alright model to compare it to, but that breaks down real quick.
    Last edited: Apr 18, 2007
  11. Apr 19, 2007 #10
    AngeloG are you reponding to my first post, and agreeing that it flows faster in the centre of the wire? And can you explain the Chemistry model in Quantum Mechanics in more detail?
  12. Apr 19, 2007 #11
    The orbitals of last electrons "touch". In fact the orbitals do not stop abruptly but fade rapidly with distance. The consequence is that these electrons can tunnel very easily form atom to atom (and become free electrons). The energy states of these coupled orbitals degenerate and gives a very big number of states with energies distributed in a few electron-volts gap. This is what is called the "conduction band".

    No. Magnetic field will be almost the same (there may be a very minor and insignificant difference).
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