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What is impeadence of ionized air?

  1. Nov 3, 2006 #1
    what is impeadence of ionized air?
  2. jcsd
  3. Nov 3, 2006 #2


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    I've done some google and wiki searching, but I didn't find a good link. Basically, when you have a full-on arc, the impedance is very low (like a wire). The terms to search on are ionization, glow, arc, spark, etc. Spark gap protection devices for data line networks are basically short circuits when they arc over.
  4. Nov 4, 2006 #3

    I found one research article in journal of chemistry that says it is 1gigaohm AFTER ionization...which is luidicris(sp?)...
  5. Nov 4, 2006 #4


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    Depends also on how much ionisation.

    In fact, an arc is badly described by an impedance, because the V-I relationship is highly non-linear (while impedance would be the linear coefficient). As berkeman said, for a strong arc, the differential impedance can be near zero (almost no change in V for a change in I).
  6. Nov 4, 2006 #5


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    Also, unlike most materials, impedance of air decreases as temperature increases. So a spark that we see as an instantaneous eventis actually a fairly complex process. A little bit of current jumps a gap once the air is sufficiently ionized, and this currwent encounters strong resistance. The passage of current through resistance creates heat (which further ionizes the air, I believe), and causes more current to flow.
  7. Nov 9, 2006 #6
    A couple more things that needs to be taken into account are air pressure and humidity. These things can change the resistance of air quite dramatically
  8. Nov 16, 2006 #7

    assuming STP
  9. Nov 17, 2006 #8


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    With proper design, spark gaps can have very low impedances, though I'm afraid I don't know the details of what's required to accomplish this. Devices apparently exist that can switch mega-amperes (with kilovolts power supplies).

    Some web references:


    (has a bibliography to some literature on the topic, and a quick overview of some of the physics involved, which is considerable).


    sells a railgun spark gap switch, but wants a lot of money for the plans (don't know if they are on the up-and-up).


    wikipedia article about spark gaps.
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