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Why does air hold a charge?

  1. Oct 11, 2009 #1

    taylaron

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    In various electrostatic devices, static electricity is 'stored' in encapsulated containers of air with a simple conductor penetrating the wall. these Leyden Jars have a metal sheathing on the outside of the container I believe.

    If the electrons pass from the conductor through the air to the metal sheathing, doesn't the air hold or transmit a charge?
    Is it the ionization of certain gas particles in the air that causes them to hold charge?
    I would appreciate an in-depth analysis of this phenomenon at the atomic and molecular scale.

    Regards,
    -Tay
     
    Last edited: Oct 11, 2009
  2. jcsd
  3. Oct 11, 2009 #2
    Air can conduct electricity when the voltage is high enough but it doesn't hold a charge.
    A layden jar consists of a container - e.g. a jar or a bottle - with metal foil on the inside and on the outside. The metal foil is not penetrating the walls.
    The charge is stored in the metal foil. The glass or plastic walls of the container insulate the two metal foils from each other. The air inside the jar doesn't play any role whatsoever.
    So there is negative charge on one metal foil and positive charge on the other.
    The proximity of the negative and positive charges causes them to mostly cancel each other from the point of view of a static generator connected to the jar. That means that you can put a relatively large amount of charge into there before the electric forces repel additional electrons too much to charge the jar any further.
     
  4. Oct 11, 2009 #3

    taylaron

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    Thanks Dr. Zoidberg (I never thought I would say that...)
    Oh, I understand now. I'm confused on how the charge is transmitted through the air to the foil though. At a high enough voltage, yes, the air particles would ionize and they would be conductive, but i'm pretty sure the air isn't ionized at this point. Correct?
     
  5. Oct 11, 2009 #4
    Usually the charge is transmitted to the foil by a wire or a metal rod.
    In electrostatic machines there is also often charge flowing through the air.

    At what point? I don't get what you mean.
     
  6. Oct 11, 2009 #5

    taylaron

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    I wasn't aware of a metal rod actually touching the plates. I thought there was a rod entering the chamber, but not touching anything but the air. If that is correct, then the charge would have to flow through the air to the metal plates like you said.

    "At what point?" I'm referring to the electrical connection (the air) between the metal rod and the foil wherever it may be in the air.
     
  7. Oct 11, 2009 #6

    turbo

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    Leyden jars are made of a dielectric material, with conductive coatings inside and out. The interior coating is in contact with a rod that penetrates through the stopper at the top of the jay, often with the aid of a metal chain that dangles from the rod and lies on the interior coating. Charge is not stored in the air, nor in the dielectric of the jar, but on the surfaces of the coatings. The Leyden jar eventually was supplanted by capacitors, which have become smaller and more efficient over time.
     
  8. Oct 11, 2009 #7

    taylaron

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    Ok, thanks for correcting my understanding.
     
  9. Oct 11, 2009 #8

    turbo

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    You're welcome. The dielectric material separating the cylindrical plates was a matter of practicality and consistency. The real variables come from the thickness of the plate materials, and the size of the gap separating them. You could store charges on those plates even if the dielectric material was replaced by vacuum, though obviously lining a glass jar with thin metallic foil inside and out was a very practical solution.
     
  10. Oct 12, 2009 #9
    The air can hold charge as it does in clouds with help of the wind.
     
  11. Oct 12, 2009 #10

    taylaron

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    I thought dust particles in the air were attributed to the holding of charge and formation of clouds.
     
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