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Thread: how to generate large elec charge in a small ball

  1. #1 how to generate large elec charge in a small ball 
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    how to generate large elec charge in a small ball?

    The only way is FRICTION.

    and you do it for 1 hour, make the ball get 1000 V?


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  3. #2  
    Reptile Dysfunction drowsy turtle's Avatar
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    Charge is measured in coulombs, not volts.


    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  4. #3 Re: how to generate large elec charge in a small ball 
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    Quote Originally Posted by steelcat
    how to generate large elec charge in a small ball?

    The only way is FRICTION.

    and you do it for 1 hour, make the ball get 1000 V?
    How about 5 MILLION volts to ground in much less time than an hour ?

    http://en.wikipedia.org/wiki/Van_de_Graaff_generator
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  5. #4 Re: how to generate large elec charge in a small ball 
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    Quote Originally Posted by steelcat
    how to generate large elec charge in a small ball?

    The only way is FRICTION.

    and you do it for 1 hour, make the ball get 1000 V?


    I've got a few doubts:

    Firstly, why the hell do you want to know?
    Secondly, if your answer to my first question is the pursuit of knowledge, what's the big deal about a small ball or a big ball or small charge or big charge.

    You just wanna charge some object.What you can do is knock off a few electrons (positive charging) or, maybe introduce a few (negative). You may induce a charge on one part of the object by bringing another charged body in vicinity (though the net charge remains essentially zero.
    Beyond Equations,

    Pritish
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  6. #5  
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    They are called Van Degraff generators, look it up.
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  7. #6  
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    hmmmm... This sounds SOOOO familiar... Could you be wanting something that resembles anything to do with EMP?

    Sadly, I actually have questions on it, the biggest of which is the actual plausibility of PRODUCING an emp that would be large enough to affect something, say, 20 feet away, while still being small enough to carry around? (this is more a question stemmed from movie myths than anything else, so the physical science and theory into this is of more a concern to me than the application: not interested in the application, really, aside from adding it to the 'I'll never use this in a million years' file)
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

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  8. #7  
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    Quote Originally Posted by Arcane_Mathematician
    hmmmm... This sounds SOOOO familiar... Could you be wanting something that resembles anything to do with EMP?

    Sadly, I actually have questions on it, the biggest of which is the actual plausibility of PRODUCING an emp that would be large enough to affect something, say, 20 feet away, while still being small enough to carry around? (this is more a question stemmed from movie myths than anything else, so the physical science and theory into this is of more a concern to me than the application: not interested in the application, really, aside from adding it to the 'I'll never use this in a million years' file)
    Some EMP simulators use a Van de Graff generator discharged through an overheat wire above a ground plane to produce a plane wave that simulates the real thing. But those are elaborate set-ups and the pulse is pretty well confined to the test area.

    The apparatus is decidedly "bigger than a bread box". You won't carry one in your pocket, your pickup truck, or even on a large transporter except in pieces.

    Here is an article on the Trestle facility. The Ares facility is nearby and a bit smaller.

    http://www.cerezo.name/archives/000006.html

    Yes, that is a B-52 on the test bed.

    What you see and hear in the movies regarding EMP is not accurate.
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  9. #8  
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    I didn't think so, but i was curious. Another question, what matters more in the EMP wave; the charge|charge density(coulombs|coulombs/meter) or the potential(Voltage)?
    Wise men speak because they have something to say; Fools, because they have to say something.
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  10. #9  
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    Quote Originally Posted by Arcane_Mathematician
    I didn't think so, but i was curious. Another question, what matters more in the EMP wave; the charge|charge density(coulombs|coulombs/meter) or the potential(Voltage)?
    There is no charge/density in an electromagnetic wave. Units of coulombs/meter are not used in anything with which I am familiar. I can't imagine to what those units might pertain.

    The correct units for the intensity of an electric field are volts/meter. When people use the term EMP they usually are referring to EMP generated at very high altitudes by recoil of electrons following Compton scattering due to gamma particles from a nuclear event, HEMP. There are other effects that result from closer proximity to the blast, source region EMP and from x-ray effects on cabling and other components, system generated EMP or SGEMP.

    High altitude EMP is usually modeled as a high intensity plane wave with an electric field intensity of tens of thousands of volts per meter. It has a very fast rise time and hence is concentrated at high frequencies. Because of the high frequency nature of the pulse it is relatively easy to shield electronics against EMP. If no protection is provided then there is high likelihood of upset or damage to electronic equipment. But if cabling is filtered, and if cables and boxes are shielded little effect is likely. The problem is that these simple protections are generally lacking in civilian equipment.
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  11. #10  
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    Clearly I knew little about the phenomenon, thanks for clearing it up. I knew that the nuclear bombs caused it, but I didn't know exactly what it was that made it work. Volts/meter, and the farther away from the epicenter you get, the weaker the field gets, exponentially right?

    And tbh, I pulled the 'charge density' bit out of my butt, I was just taking a stab at what it could be. How do you measure voltage/meter? Or, atleast, how does the voltage over an area work, would there be high points and low points or would it bang out pretty uniform?
    Wise men speak because they have something to say; Fools, because they have to say something.
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  12. #11  
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    Quote Originally Posted by Arcane_Mathematician
    Clearly I knew little about the phenomenon, thanks for clearing it up. I knew that the nuclear bombs caused it, but I didn't know exactly what it was that made it work. Volts/meter, and the farther away from the epicenter you get, the weaker the field gets, exponentially right?
    No. Electromagnetic fields from a point source decrease in intensity as the inverse of the square of distance. But if the source is a infinite plane then the fields do not degrade at all with distance. A normal EMP is somewhere in between, but is often adequately modeled as a plane wave for regions on the surface of the earth below the blast. The effects would be fairly widespread, basically covering a continent.

    And tbh, I pulled the 'charge density' bit out of my butt, I was just taking a stab at what it could be. How do you measure voltage/meter? Or, atleast, how does the voltage over an area work, would there be high points and low points or would it bang out pretty uniform?
    Any normal field strength meter will give you intensity in volts/meter. Basically you measure the potential difference between two nearby points and divide by the distance.

    There is no such thing as voltage over an area. What you can measure is power, which is determined by the Poynting vector for an electromagnetic wave (the cross product of the electric and magnetic fields). It can be uniform or it can vary in space. For a typical EMP I would it expect it to be fairly uniform over modest changes in distance. EMP simulators try to produce a uniform plane wave.

    It is just a rather special type of radio wave. A short duration, high frequency, pulse of very high intensity.

    If you are really interested, you need to start by reading a good text on electrodynamics. The classic text is Jackson's Classical Electrodynamics. Jackson is a good class for a first-year graduate level physics class. If you want something that is more accessible to undergraduates then I suggest either Marion's Classical Electromagnetic Radiation or Hayt's Engineering Electromagnetics. You need that as basic background in the science of electrodynamics. Then you can take a look at bulletins on EMP awareness, which I think can be obtained from open government sources.

    Beyond generalities of the type that have been discussed here, specific information on nuclear EMP (particulary field strength and rise times) gets into classified material.
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  13. #12  
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    your initial question really is unclear, small ball-ball of what, how small?r is the charge in a ball?
    Small and large charge don't go together either.usually need a relatively large collector sphere .
    1000 V is not large as far as static ec=lectricity is concerned- get that rubbing a cat on a rubber bar.
    How did EMP get into this?
    Maybe if you explained your goal these folks might help.
    Small
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