Gut understaing of some electrical phenomena

Discussion in 'Physics' started by Gilberto Pacheco, Dec 20, 2014.

  1. Gilberto Pacheco

    Thread Starter New Member

    Dec 20, 2014
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    Hello everyone.

    This is my first post here, so sorry if I'm asking in the wrong place.
    I am an Electrical Engineer form Brazil and I discoverd this site http://amasci.com/ele-edu.html a while back and since then it's been a great source of knowledge and gut understanding of electrical phenomena.

    One very thing I always wanted to know and couldn't figured it out up to now, is this:
    If you have two bodies charged up, like when you scuff your shoe on a carpet, one of them will aquire electrons from the other and hence be negatively charged and the other positively charged.
    Ok, so far so good. Then we say that the person is "charged up" and when this person sticks his finger to a metal objetc (don't know why it has to be metal, first question) there is a flow of electrons from the person to this metal objetc. But now is my question:
    Back there in the begining, how the carpet regaind or gave up its lost or aquired electrons.
    I mean this information is not showed on books and I have tried to find an explanation online but I couldn't.
    It is like the explanation from lightning.
    We are told that the base of the cloud is negatively charged and the top is positively charged. When the lightning happens, the excess of electrons from the base goes down to the earth.
    Ok, but what happened to the positively charged top?
    And why, doesn't the negatively base canceled out with the positively top in the first place?
    Could anybody help me with those?

    Thank you.
     
  2. nsaspook

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  3. studiot

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    The electrons you rub off the carpet onto your shoes are probably never returned to the carpet.

    The air molecules pick up electrons as they brush past objects and deposit these on the carpet.
    Other moving objects (eg cats, roaches, more air molecules whatever) also pass these objects and deposit electrons onto them

    and so on and and so on.

    So the electrons go round in a huge circle from one object to another, moved on by passing mobile objects such as shoes, air molecules, and so on.
    Equally objects in very dry air can take a long time to loose or regain a charge.

    Water vapour molecules are particularly good at moving electrons so the redistribution happens rapidly in moist atmospheres
     
  4. amilton542

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    Nov 13, 2010
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    I stuck a piece of cling film to my bedroom wall several days ago. It's still there. Cool, huh?
     
  5. alfacliff

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    Dec 13, 2013
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    why metal? because it is a conductor. one thing about lightning I dont understand is how a bunch of water droplets act like the big ball on a van degraff and charge up together without repelling each other. why dont clouds expand and contract when they charge up and discharge?
     
  6. nsaspook

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    The clouds water droplets are moving (and creating a electric energy field from charge separation) because of the thermal and mechanical energy in the structure of the cloud formation movements. The repulsive and attractive forces from the charges are present but don't exceed the other energy sources.
     
  7. alfacliff

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    but how do the droplets, seperated as they are, act as a large conductor charged up with millions of volts? the droplet spacing is huge compared with the charge on each droplet, and the foltave needed to spark between them when discharging them.
     
  8. studiot

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    It is thought that the charge is carried by ions of water vapour (ie gas) not the droplets see page 4 here (though you may be interested in the rest of the pdf)

    http://www.colutron.com/download_fi...cQFjAE&usg=AFQjCNHngqqtXX5OqiqGpfD3sGQsy0uy_g
    can't seem to get the url to work so here is the pdf
     
    Last edited: Jan 9, 2015
  9. alfacliff

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    where does the energy to ionise the water vapor come from? compared to ions, water vapor droplets are huge. wouldnt it take quite a bit of energy to ionise them?
     
  10. nsaspook

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    Last edited: Jan 9, 2015
  11. studiot

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    Water vapour is a gas. Droplets are liquid and as you say they are huge by comparison with gas molecules.

    The individual molecules are ionised, not the droplets, though I don't doubt that some droplets pick up some charge.

    The energy is initially of thermal origin, and large due to the high latent heat of water; it then becomes kinetic energy, where the friction that causes the ionisation occurs.
     
  12. alfacliff

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    flying through a cloud or walking through fog, you notice that it is made up of small droplets, I have never seen a gas, but are the molecules of a gas as far apart as the droplets of clouds? how conductive is fog? does it act like one mass or individual droplets? if the air between the droplets ionised, it would glow.
     
  13. studiot

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    Perhaps I should have said water vapour is an invisible gas.
    (Steam or condensation (fog etc) that we can see is a mixture of water droplets and vapour)

    The molecules of all gases constantly bump into each other, that is the kinetic theory.

    Most ions do not glow. The glow we can see in ionised air is not from the ions themselves but from the passage of electricity conducted by the ions in the air.
     
  14. #12

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    Nov 30, 2010
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    There are several gasses you can see. Two of them are chlorine and nitrous oxide.
    I'm sure there are chemists here that can put me to shame about how many visible gasses exist.
     
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