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B What makes the charge gradients within a cloud?

  1. Jun 12, 2016 #1
    Hi!

    It has been explained to me in another thread of mine that there actually can be lightning/thunder within a cloud.

    My question now is how there can be such high charge gradients within a cloud that this can happen and of what types of ions and electrons there is and how they have emerged.

    Because it's for sure not gravity, or?

    As the amateur I am I will try a explanation of my own: a cloud consist of water vapor, this vapor has then become ionized by photons from the sun but if hydrogen are free ions and oxygen free ions, there should be a "big bang", right? And this still not explains the obvious gradients in space.

    Best regards, Edison
     
  2. jcsd
  3. Jun 12, 2016 #2

    Simon Bridge

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    Things to think about: real life is messy...
    You can have molecular ions, and objects like dust and water droplets can become charged.
    Photoionization (sunlight) is not the only way that objects can become charged in Nature.
    Objects can become charged by friction or interaction with ions carried in the air: ie by wind.
    Similarly, wind can separate out charges in a region just by blowing through it, and different clouds may carry different potentials depending on their histories.
    It may be that the potential difference is between a region carrying a large net negative charge and another region carrying a smaller net negative charge, with a static discharge (lighting) occurring as these regions approach.
     
  4. Jun 15, 2016 #3
    No simple answers here, then :)
    Interesting.
    The only way I could think of with my limited knowledge.
    Friction brings me back to how a ballon may be charged by rubbing a plastic stick on it, it then attaches to ones hair :)
    Interesting.
    This approach of thinking was educational, a potential difference can then consist between two regions of only electrons but with different number of electrons, right? But why not? Potential is defined by number of charge and here we only have a difference in number of charge. At the same time, why and how is there a difference in charges? As I have read the above one answer may be the wind and when the wind slows down, these regions approaches with lighting as the result.

    But getting back to what you have said, ionization by sunlight is not the only way objects can become charged, friction is also important. But I still don't see how there can be so much free charges (weather they are molecules or electrons). Maybe two water molecules rubbing against eachother can strip electrons so that there are water molecules of positive charge along with electrons of negative charge just by, as you have told me, friction? And wind makes these charges move away or toward eachother which finally, when they are close, makes lightning? It's hard to see though.

    Thanks Simon for your answer, it educated me!

    Best regards, Edison
     
  5. Jun 15, 2016 #4

    davenn

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    yes, one region is just more positive than the other
    remember it's primarily the movement of electrons and positive ions ... electrons are being stripped off atoms resulting in charge separation

    not quite see previous comment and the following ones I make

    yes .... consider we are talking about zillions ( uncountable numbers) of atoms being stripped of electrons
    you commented on the rubbing of a balloon experiment not really big sparks being formed
    take that a step further, when you rub you feet across a carpet and go to touch a doorknob etc you can produce a 5mm spark ~ 10,000 - 50,000 Volts
    another step further, a Van de Graff generator, a major electron stripping operation. a few million volts and much larger sparks

    now to a thunder storm cell say 20km wide and 12,000 metres high (15 miles and ~ 38,000 ft) more electrons being stripped from atoms than you could ever imagine by the friction of water droplets, ice crystals and full sized hail stones all being carried by huge updraughts within the storm cell
    10's to 100's of millions of volts and huge charge build ups resulting in 10's of 1000's of amps in a single lightning bolt.


    no, not quite the way you stated it
    there is that charge separation with in the cloud(s), by the process I described, producing the inter and intra cloud discharges
    there is also a buildup of separation of charge between the ground and the base of the clouds resulting in huge potential differences

    When that potential difference ... the value of the electric field .... that is formed between the cloud base and the ground builds and finally reaches the breakdown voltage of the air gap insulation, a lightning charge will occur



    Dave
     
  6. Jun 16, 2016 #5
    Thank you Dave very much for trying to explain this to me, yet I am mainly interested in lightning within a cloud and I still not really se it happening. Friction seem more important than I ever could have thought. Nice example with the walking on a carpet and touching a handle, gave me a clue of what it's all about. But charge separation within a cloud, why and how? If two water droplets, ice chrystals or full sized hail stones are rubbed together, why should the ions and the electrons get separated? Because they need to get separated, at least for a while, so that a high potential difference can be built up, right? Otherwise they just separate and recombine, I think. So somehow these electrons and ions get separated over a considerable time and then, suddenly, they crash into eachother (breakdown voltage). Because even if there are "zillions" of atoms being stripped of electrons, they need to reside somewhere for a huge potential difference to occur. If the atomes are stripped of electrons all the time, the may also recombine all the time. There thus seems to be some kind of accumulation of charge which then discharges at some convenient opportunity, which is not fully defined.

    Best regards, Edison
     
  7. Jun 16, 2016 #6

    davenn

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    it's all in the response I gave .... here it is again

    no

    as the electrons are stripped from atoms that is a charge separation. The positive ions ( atoms with less than their usual # of electrons) get moved away from the negative charges ... this results in an electric potential (and electric field) building up over a distance ( the gap between them) as with the cloud to ground strikes.
    when the electric field exceeds the breakdown voltage of the gap, a lightning discharge occurs. There is no difference to this occurring be it with /between areas of the cloud and between the cloud and ground.


    Dave
     
    Last edited: Jun 16, 2016
  8. Jun 16, 2016 #7

    davenn

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    here's a few pictorial examples ......

    ec%20chrg%20in%20tsrm.gif

    http://icons-ak.wxug.com/i/severe/lightning_explainer.png

    charge-distribution.png




    cheers
    Dave
     
  9. Jun 17, 2016 #8
    Once again I thank you Dave for trying to explain this to me. However I fail totally in understanding charge separation. Your kindly provided pictures looks nice and gives me more understanding generally but specifically, the charge separation with focus on staying separated and accumulate remains an enigma to me. Because where does the ions and electrons go? Why not just recombine? Why build up a huge potential difference and then discharge, I don't get it.

    I expect no answer to this, you have put down enough time and effort into helping me, thanks.

    Best regards, Edison
     
  10. Jun 18, 2016 #9

    davenn

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    my previous comments and the images clearly show where they go

    recombine with what, they have become greatly separated over many kilometres as shown in the images ... between clouds and ground or between different regions in the clouds

    I'm not sure how to be clearer .... the build up of the potential difference continues UNTIL the electric field reaches the breakdown voltage for that particular sized gap. Then the discharge occurs causing a recombination of the + and - charges and then the process repeats over and over until the storm dies out.
    The charge separation can only occur when there is good updraught within the storm cell. As the updraught strength diminishes, so does the charge separation



    Dave
     
  11. Jun 18, 2016 #10
    I think this is the explanation I was looking for. Because how can charges of equal sign otherwise accumulate? It is even hard to understand how rubbing your feet on a carpet can strip and accumulate electrons within your body and then just discharge when you touch a doorknob of metal which even only may be sitting in a wooden door, that is the electric discharge does not even have to have a low ohmic path to the ground. It even feels like the discharge happens because the doorknob is made of metal without other considerations. As if metal itself accepts a bundle of electrons or even crave for it ;)

    Best regards, Edison
     
  12. Jun 18, 2016 #11

    davenn

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    that's indeed how they separate

    it doesn't need a path to ground ... it just needs a path to a place where the charge amount is different .... there is no grounds in the cloud are there ?

    it works better with metal as it is a good conductor. remember your body can collect that charge then discharge it to another object eg remember you can charge yourself up and then zap the person standing beside you, but neither of your bodies are made of metal.
    Don't go there ! it's an inanimate object, has no feelings


    Dave
     
  13. Jun 18, 2016 #12

    Dotini

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  14. Jun 18, 2016 #13

    NascentOxygen

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    You can often see lightning flashes within the turbulent black cloud billowing from the vent of an erupting volcano.
     
  15. Jun 19, 2016 #14

    davenn

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    yup, indeed, and the process of charge separation is just the same
    instead of cool wet materials in a cloud it's hot dry materials in the ash plume



    D
     
  16. Jun 19, 2016 #15
    Hi Dave!

    This was a real good explanation, thanks!

    By the way, I didn't really mean "crave", my english is not so good :)

    Best regards, Edison
     
  17. Jun 19, 2016 #16
    Okey, Dave.

    Maybe I should quit now but I am qurious, do I dare ask the question of charge accumulation? I think I understand charge separation in the aspect of stripping and friction, but I do not understand how charges with the repelling equal sign can accumulate. Let's again consider the simple situation of me walking on a carpet stripping electrons from it, why would I collect electrons at all? Is it because I'm positively charged to begin with, or? If I'm not positively charged to begin with, why would the electrons enter my body and stay there (until I touch something with a less/higher amount of electrons)? I really don't grasp this accumulation part.

    Best regards, Edison
     
  18. Jun 19, 2016 #17

    davenn

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    I'm not sure I can answer that overly well ...
    @Dale @mfb can you help please ?

    My first thought would be is that the forces separating the charges is stronger than the repelling force between like charges

    You are likely to be at or close to neutrally charged ( equal numbers of positive and negative charges)

    some reading up of electrostatic charges may help ....

    a couple on the Van de Graff generator....
    https://www.boundless.com/physics/t...statics-138/van-de-graff-generators-496-6320/

    http://www2.physics.ox.ac.uk/accelerate/resources/demonstrations/van-de-graaff-generator

    a couple on general electrostatics ....

    http://phun.physics.virginia.edu/topics/electrostatics.html

    http://sardarsinghsir.com/XI-XII/XII-BC/I-v1.1-BC-Part-I-Electrostatics.pdf


    reading all those will keep you busy for a while :wink:



    Dave
     
    Last edited: Jun 19, 2016
  19. Jun 20, 2016 #18

    mfb

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    The triboelectric effect (charge separation by contact) is complicated, and not always intuitive - you can get some charge separation even if you rub two identical materials.
     
  20. Jun 20, 2016 #19

    Dotini

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    I think it is fairly well agreed upon that the surface of the Earth is negatively charged. It seems to me that a person standing barefoot in intimate contact with Earth is going to acquire the same charge as the Earth. Agreed?
     
  21. Jun 20, 2016 #20
    Would you further elaborate on that ? I am quite confused how this would be possible.
    The wikipedia article is full off "citation needed" and it didn't really explain why charge seperation between the same materials might work.
    It said, that some materials have other "chemical potentials" and so some charge is more likely to accumulate there.
    However if both substances are identical then there really shoudn't be any charge seperation.(When you base your assumption on only that idea)

    And has there been any consensus of what the "dominant" process is in charge genertaion in a cloud ?

    Speculation alert o0): I had an idea for a charge seperation process.
    Maybe because the droplets are often supercooled(i have no source for that) they will freeze a little upon contact with an snowflake or ball of hail, which might push out ions at different speeds causing some to be captured more in the ice than others.
    To be honest I have no clue about this ...
     
    Last edited: Jun 20, 2016
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