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Does Air Have A Macroscopic Grain Structure?

Discussion in 'General Electronics' started by Mark Thorson, Aug 1, 2004.

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  1. Mark Thorson

    Mark Thorson Guest

    by Marshall and Stoye (Spon & Chamberlin, 1906),
    pages 65-66:

    "For ordinary sparking experiments the negative electrode should
    terminate in a fairly large brass disc, the positive being a needle
    point adjustable as to distance, but moving opposite the centre
    of the disc. By this means the longest sparks can be obtained.
    It will be noticed that the sparks constantly strike fresh places,
    and they almost invariably traverse very crooked paths through
    the air. In this respect they are like lightning flashes -- 'small
    editions' of which they really are, as a matter of fact. These
    crooked paths represent 'lines of least resistance,' the electric
    current, no doubt, finding irregularly distributed particles of
    conducting matter floating in the atmosphere."

    Is that really why electric arcs follow an irregular path?
    Is the mechanism for this phenomenon known?
    Is it the presence of dust, or something? Would an arc
    struck in dust-free air follow a smooth path?

    Or could there be an invisible grain structure in air?
    Such as local pockets with different chemical composition,
    as compared to the matrix? Would an arc struck in
    pure nitrogen behave any differently than an arc struck
    in air?
  2. crynwulf

    crynwulf Guest

    No. there is still local un-even distributions of moisture, air motion,
    molecular motion, energy level of atoms, etc.
    Arcs in pure nitrogen (or helium) do behave differently, But probably not in
    the way you are thinking.
    One explanation for the jagged paths of lightning is that it follows charge
    paths left by cosmic radiation.
  3. aSkeptic

    aSkeptic Guest

    Does air have a grain structure? It would be interesting to find out!
  4. EPK

    EPK Guest

    A "grain structure" implies crystallinity, so .. no.
    There is a substructure, which changes on fine scales (less than cm), which
    would be the length scale of interest for these effects.
  5. Mark Thorson

    Mark Thorson Guest

    Wood has a grain structure, but it is not crystalline.
    I meant inhomogeneities on the scale of millimeters
    to centimeters that could be responsible for the
    crooked path of electric arcs.
  6. Yukio

    Yukio Guest

    I would suspect observing the operation of a "Wilson Cloud Chamber " would
    be instructive, so would watching a working "Geiger Mueller Counter tube"
    would have to be one with a transparent window though ! Both examples show
    the path of an Ionizing particle in real time, through a gas at near
    atmospheric pressure. I suspect that under the conditions described below
    "For ordinary sparking ~~" if one could vary the high voltage source, I
    would not be surprised to find that there was a curve very similar to the
    normal operation of a GM counter with a threshold, linear, proportional, and
    avalanche portion. The only difference being that the GM counter gas is
    optimized for best operation.

    Yukio YANO
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