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Question about electricity and atoms, electrons.

Discussion in 'Electronic Basics' started by Ole, May 16, 2004.

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  1. Ole

    Ole Guest

    When there goes a electric current trough a wire, is it just the
    electrons that moves / jumps from atom to atom and the atom is not
    moving or does the atoms also move?

    How does the electro magnetic fields work, when you transmit a signal
    from a antenna, the atoms and electrons doesn't move, the electrons on
    the atoms just rotate the same way as the atom it's get affected by -
    is this right?


    Regards
    Ole
     
  2. In metals, only the electrons move, and only a small fraction of them,
    at that. The atoms are held in rigid positions (with only a little
    thermal jiggle allowed) by electrons that each atom shares with its
    nearest neighbors. But in metallic elements (and mixtures of metallic
    elements) there are one or at most two electrons from each atom that
    are shared over a larger volume than just the nearest neighboring
    atoms. These conduction electrons amount to a gas in which individual
    electrons can wonder at random, throughout the metal. This gas also
    drifts if a tiny electric field is present in the metal. That slow
    drift is ordinary electric current. The electron wind blows quite
    slowly during ordinary current densities, but the electric field that
    motivates to propagates through metals at nearly the speed of light.

    In semiconductors there are positive equivalents of electrons that are
    nothing more than the absence of conduction electrons (balanced by an
    absence of protons in the atomic nuclei) that have properties very
    similar to conduction electrons (they can hop from atom to atom),
    except that they have a positive charge instead of a negative one.
    They are commonly referred to as holes. In solutions, gases and
    plasmas atoms missing one or more electrons are called ions and since
    they are free to move, they can contribute to current (movement of net
    charge) in addition to free electrons. In high energy physics there
    are also rare particles like anti electrons and a whole zoo of other
    particles that have electric charge and can take part in current.
    Wish I knew, exactly. The idea is that anytime an electric field
    changes strength, it generates a magnetic field (at right angles to
    it, no less). And any time a magnetic field changes strength, it
    generates an electric field (at right angles to it, also). So even in
    completely empty space, electric and magnetic fields make each other
    in a repeating process that propagates as a sort of wave at the speed
    of light that replicates the frequency that launched it.
    Do a search for Maxwell's equations is you are interested in how
    compactly this process (and all the other linear properties of
    electromagnetism) can be described.

    When such a wave reaches a conductor, some of the energy in these
    fields generate voltage (electric fields over some distance) and
    current (charges that move in response to electric field) in that
    conductor, also. And If the conductor is appropriately sized and
    shaped to cooperate with these waves, a usable signal can be extracted
    from the conductor as the waves passes. This works in reverse, also.
    If a signal is applied to the same shaped conductor so that it carries
    current at the wave frequency, it will launch electromagnetic waves
    into space. Keep in mind that everything I have told you is wrong at
    some level of accuracy. The only way to precisely describe what is
    known about what is going on is with mathematics.
     
  3. Bill Vajk

    Bill Vajk Guest

    Nicely done, as usual, however I'll add this tidbit. You
    can correctly think of the "electro magnetic field"
    transmission you're describing (radio waves) in
    exactly the same context as visible light but at a
    different frequency. What you sorta kinda do is
    "boil off" energy from a radiating element of some
    sort which has a way of moving through space or many
    real mediums, like air, till it hits something that
    detects its presence as an effect.

    There is an entire huge spectrum of electro magnetic
    waves which include things like light and x-rays in
    addition to the radio frequencies most people
    associate with electro magnetic waves. Try
    the links:

    http://www.phy6.org/stargaze/Sun5wave.htm
    http://www.colorado.edu/physics/2000/waves_particles/
     
  4. jw

    jw Guest

    Check out the book "Electomagnetics Explained" by Ron Schmitt.

    --jw
     
  5. In my view, the easiest way to get to grips with some basics of EM is by
    the basic overview of the complicated account, that we usually only
    learn about much, much later. That is, quantum electrodynamics, or QED.

    QED explains *all* of electromagnetic phenomena by the momentum exchange
    of photons between charges. That is, *all* electro-magnetic fields are
    essentially, nothing more that billions of photons moving about in
    strange (statistical) ways. It is not the direct motion of electrons (or
    ions) moving that actually constitutes the "real" electric current, they
    usually move very, very slowly, where as electromagnetic effects travel
    at the speed of light. The falling domino effect is the better way to
    view what "current" is. That is, as soon as electron moves, its photon
    exchange with its nearest electrons is felt essentially, instantaneously
    (speed c), and this is propagated along to next ones. The idea of
    momomentum exchange as the EM force can be illustrated by two skaters on
    ice throwing balls at each other. Each throw causes the thrower to move
    backwards. The harder bit is accounting for an attractive force, but
    this is all in the (complicated) wash in QED.


    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
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