Talk:Van de Graaff generator
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[edit] accumulating voltage?
The article says...
A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high voltages on a hollow metal globe.
This doesn't quite make sense. How can something "accumulate" voltage? Better to say the Van de Graff machine accumulates charge.
Korkscru 07:07, 4 November 2007 (UTC)
[edit] Belt charging
Maybe there are two different versions, but the version I made used the triboelectric effect with a rubber belt and rollers made of different materials. The power supplied was only used to drive the motor. Am I right in thinking there are two different kinds? If so, both should be addressed. - Omegatron 14:21, Mar 30, 2004 (UTC)
I agree with both. I did not look at the charging and un-charging mechanisms on the MP tandem I used, but I believe its operation was closer to the description in the article. It did have a high voltage supply to charge the belt. On the other hand, small demonstration Van_de_Graaff_generators I have seen use unlike materials, as above. I don't know whether nuclear reactions have been induced with this type of charging. --David R. Ingham 18:31, 7 August 2005 (UTC)
I built a VDG using the triboelectric effect. The belt is rubber, the upper roller is nylon, and the lower roller is teflon. On a good day it approaches 500KV at 30uA. The voltage of any VDG is limited by the effective diameter of the "sphere" and the length of the column. The current is a function of the belt width and speed and of the charging effectivness of the rollers and combs. A belt charging power supply may increase the current, but would have little effect on the voltage, unless the column or belt are leaky (resistive) due to contamination or moisture from high air humidity. --Etymolog 03:57, 15 December 2006 (UTC)
There is a type of unit that is popular in schools that uses an incandescent light. Many people assume that the light is just there for effect - in reality the light is actually a source of electrons - as used in a thermoelectric valve. The electrons are given off from heating of the tungsten, and are deposited onto the belt. Of course these units do not work well with CFL's Vk2tds (talk) 22:09, 27 December 2007 (UTC)
[edit] Popular name for nuclear reaction experiments.
I agree with this edit, but would like to hear other opinions. The exhibit at the Smithsonian is or at least was called "Atom Smashers". I think that is archaic, but I am not sure.
[edit] Sphere Connection
The whole thing about connecting the wire to the inside of the sphere is false. i made a vdg machine and connected it to the outside of the sphere, and it worked just fine. anyway outside and inside are relative terms, thus the whole concept of ice pail effect does not make sense to me.Also going by that logic a circular plate would not carry any charge as it would not know which side to put the charge on(it can be assumed to a sphere of infinite radius) Pranay
- The wire can be connected to the outside of the sphere; the crucial point is to have the charge removed from the belt inside the sphere, where there is little electric field. Theoretically, a closed conducting shell has no electric field inside, no matter how much charge is on the outside. Although the sphere has an opening, only a small amount of electric field will get in. The principle is that like charges try to get as far away from each other as possible, so they concentrate on the outside of conductors. Charge liberated from the belt will migrate to the outside of the sphere, if given a wire attached to it anywhere. --ChetvornoTALK 15:24, 29 December 2007 (UTC)
- A circular conducting plate does have the same amount of charge on both sides, but the charge is concentrated on the rim, as far away from the other charges as possible. --ChetvornoTALK 15:24, 29 December 2007 (UTC)
[edit] van/Van
Why is it not "van de Graaff"? Isn't this more consistent? Dysprosia 10:24, 24 April 2006 (UTC)
- Due to current technical limitations, Wiki articles must start with an uppercase letter. If you feel stringly about this, there are templates ({{lowercase|correctname}} and/or {{beginwithlowercase|correctname}}) that you can insert at the top of the article to flag the more-correct capitalization.
- Atlant 19:48, 8 August 2006 (UTC)
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- Actually, that is not a "more-correct capitalization". Many authorities support initial capitalization of surnames like this whenever they are used without a preceding name or title, even in the middle of a sentence. Gene Nygaard 04:45, 15 December 2006 (UTC)
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- Furthermore, in this particular example, Robert Van de Graaff probably should have a capitalized V even with the name in front of it. Gene Nygaard 04:48, 15 December 2006 (UTC)
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[edit] Schematic view
I've just uploaded the picture, but I think, it is not perfect: see the talk page at the Wikimedia Commons. -- Harp 15:24, 30 June 2006 (UTC)
[edit] Vacuum?
Both this article's Pelletron section, and the main Pelletron article, mention "a further development is the use of vacuum" ... uh, major modern VdGs use pelletron chains and SF6, not vacuum, as a terminal insulator. If there's some hobbyist out there firing up vacuum-insulated Van de Graffs in his or her garage, this person should get a radiation badge to monitor their x-ray dosage! —The preceding unsigned comment was added by Bm gub (talk • contribs) .
[edit] More bang for the buck?
Can anyone tell me why small commercially available (for about $450) Van de Graaff generators with 14 " diameter globes are said to produce potential differences of about 400,000 to 450,000 volts, and yet Van de Graaff's huge original machine (15 ft globes), at the Boston museum of Science, only generates a potential difference of about 2 million volts? My supposed 450,000 volt device is only capable of producing a 12 " discharge on a really good , very dry day, yet I've seen machines in some science museums throw discharges that looked like bolts of lightning clear across the room. I had always assumed the voltage of such sparks to be a couple of orders of magnitude greater than that of my little machine.
- Umm, marketing? ;-)
- More seriously, the first few tens of kilovolts are easy, and after that, each additional volt becomes more expensive. There's also the question of current. That machine at the MoS can produce substantial current as well as 2MV; it recharges fast enough to throw a multi-megavolt spark every second or two, so there are quite a few electrons being pushed around (and a lot of primary power being consumed).
- The usual value assumed, BTW, for the breakdown voltage of air is about 3KV/mm, but corona discharges obviously have a huge impact on reducing that value or the MoS machine would never produce the sparks that it does.
- Interesting link (PDF):
- Less technical link:
- Atlant 16:10, 30 August 2006 (UTC)
[edit] Schematic view
The starting description talks about E1 and E2 electrodes. It would be easier to understand if the schematic view showed those electrodes as well.
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- and/or if the callout numbers in the schematic view were explained in the description.
Mcswell 01:40, 24 October 2006 (UTC)
[edit] The original generator
Why isn't there a picture of the original gnenerator???? Also, a note should be made to describe that the orignal generator's spheres were not always fused together and that the spheres doubled as an office space. I'll probably go dig up the sources this week and take a picture.Adam Y.
[edit] Leyden with Danger
Heed the warning. A pint-size Leyden Jar can be lethal. A while back, my wife asked me to build her a simple Leyden Jar that she could show to her 2nd grade class. She already has my small Science First Van de Graaff Generator, so I warned her not to let the Leyden Jar near the operating Van de Graaff Generator. She did as she was told. However, I recently was demonstrating my large Van de Graaff Generator to a group of Boy Scouts in an Electricity Merit Badge class and had left the Leyden Jar on the floor near the Van de Graaff Generator. After the demonstration, I casually picked up the Leyden Jar and pointed my finger at the metallic-painted ping pong ball at the top of the jar.... I remember a flash of extreme pain, after which one of the other instructors said he hoped I don't normally use such language in front of boy scouts. --Etymolog 04:47, 15 December 2006 (UTC)
- Thanks for the warning! Van de Graaffs are usually thought of as harmless because of the small current, but capacitors can accumulate enough for a lethal shock. Caveat emptor. --ChetvornoTALK 16:30, 29 December 2007 (UTC)
[edit] Graaf or Graaff?
The title and first line don't agree. Deizio talk 08:51, 21 January 2007 (UTC)
[edit] Another external link
I know of a page that shows you how to construct a Van de Graaf generator with pieces you would usually call trash. The site is here: [1]. Please tell me if it would be a good addition to the external links section. Slartibartfast1992 16:32, 10 February 2007 (UTC)
- Oh, yeah. That'd be better. I'll just go ahead and add it.Slartibartfast1992 00:46, 26 March 2007 (UTC)
[edit] Hair
Why no mention/explanation of the hair-stnading-on-end phenomenon?
[edit] A small error?
This is a wonderful article, but I had a question about one small point of the explanation of operation. In addition to the transport of positive charges to the sphere, the example shows a transport of negative charges in the other direction, sprayed on the belt by E2, the sharp electrode in the sphere: "the high potential difference ionizes the air inside the sphere, and negative charges are repelled from E2 onto the belt". Isn't the inside of the sphere at nearly constant potential? The only electric field inside the sphere should be from the tiny amount of positive charge on the portion of belt inside the sphere. So what creates the negative ions? The Van de Graaff explanations I've seen that show transport in both directions, it is caused by the triboelectric effect of the upper pulley. --ChetvornoTALK 16:19, 29 December 2007 (UTC)
