Talk:Van de Graaff generator

accumulating voltage?

The article says...

A Van de Graaf 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)

It is used to generate very high voltages of the order of a few mega volts which is then applied to accelerate charged particles to very high velocities. — Preceding unsigned comment added by Maharajdhar (talk • contribs) 05:32, 7 February 2013‎ (UTC)

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)

I am wondering about the physical chemistry of the Van De Graaf generator, do the protons accumulated come from the hydrogens on the hydrocarbon rubber belt or nylon roller

also, I have seen pictures where a pH color changing item like litmus will turn different colors at electrolysis electrodes as a result of hydronium as well as hydroxide ion concentration; if I put a little bit of litmus water on the big accumulator( ) will it show acid pH as a result of proton accumulation; I think that it would which makes it a pleasant thing to bring to a van de graaf generator demonstration

there are dry chemicals known as superacids; ultraprotonated I think these will repel moving protons, if I cover all of the big accumulator with a layer of dry superacid aside from a cm2 will that area have much larger measurable charge; if that is true could I paint a proton circuit on the big accumulator ( ) with superacid to create shifting litmus water changes —Preceding unsigned comment added by 140.211.106.254 (talk) 02:01, 3 July 2008 (UTC)

I've read about VDGs that used a high voltage source applied to the belt. What's the point of the belt then. It would only act as a diode. Also, the light bulb mentioned in this discusion is not a source of electrons. It's a visual way of showing the current that is charging up the VDG. I think that the VDG is poorly understood by so called experts. I find the discusion areas as good as the articles are for learning. I almost never fail to at least take a look. 69.122.62.231 (talk) 01:21, 3 March 2010 (UTC)

The point of the belt is that it forces the charge carried on it to a higher potential. The motor driving the belt is the source of most of the energy input and high potential. By starting with a high voltage source at the comb it is easier to increase the current transferred to the belt and maintain a higher ultimate voltage at equilibrium. — Preceding unsigned comment added by 71.169.170.158 (talk) 00:52, 7 April 2012 (UTC)

Popular name for nuclear reaction experiments.

Re: http://en.wikipedia.org/w/index.php?title=Van_de_Graaff_generator&curid=52642&diff=20358302&oldid=20305308

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.

I agree with this edit too. I am pretty positive that is archaic. —Preceding unsigned comment added by 24.187.35.214 (talk) 23:44, 27 January 2009 (UTC)

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. --Chetvorno^TALK 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. --Chetvorno^TALK 15:24, 29 December 2007 (UTC)

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)

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)

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)

Van de Graaff is a Dutch surname. This surname has two parts: van de and Graaff, where the latter part is of importance. The van de is not important. The Dutch have the rule of capitalizing this minor part only if the surname is isolated. So, in Dutch, the correct forms are mr. Van de Graaff (isolated surname), and Robert van de Graaff.

82.92.241.131 (talk) 10:17, 5 June 2009 (UTC)

The Dutch standards do not apply to Dr. Van de Graaff's name. He was an American, born in Alabama, and his own signature on his patents has a capital "V". The spelling that appears in the article is correct because it is his own spelling. Snezzy (talk) 09:22, 26 January 2012 (UTC)

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)

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) .

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):

http://library.abb.com/GLOBAL/SCOT/scot221.nsf/VerityDisplay/B0900B81040BA3F6C12570750029D71F/$File/ISH05_Humidity.pdf#search=%22breakdown-voltage-of-air%22

Less technical link:

http://www.sciencebuddies.org/mentoring/project_ideas/Elec_p032.shtml?from=Home

Atlant 16:10, 30 August 2006 (UTC)

I've been inside the MOS VDGG, so perhaps I can give another answer. It is the SAME machine as the "Round Hill" machine and the one with workbenches inside; the article currently talks about these as if they were 3 different machines. (See http://cst.mos.org/sln/toe/history.html for a history of the machine.) The pair of spheres were originally about 15 ft or 5 m in diameter, and could hold about 5 MV each. They were usually used at opposite polarities, so a 10 MV spark could be made.

When MIT got the pair, they didn't have a lot of room, so they merged the spheres into a single "double-bubble". Because this is not a sphere any more, most of the charge accumulates at the ends, and the max voltage is around 1 MV now except maybe on very dry days. After MIT got tired of the machine, they donated it to MOS.

One column currently contains a (very wide) charging belt; there is an array of needles spraying charge onto it, so the charging current is indeed very large as Atlant suspected, and the polarity of the spray can be reversed so the spheres can go to either +1 MV or -1 MV and a few settings in between. The original DC generator coupled to the upper pulley has been replaced by an AC generator, so you can be inside and plug in 110V 60Hz equipment while the belt is running. The other column has steps and rungs so you can climb up inside, and that side still has the original wooden workbenches. (In 2010, I ran an experiment on those workbenches.) Howard Landman (talk) 10:26, 15 May 2014 (UTC)

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.

and/or if the callout numbers in the schematic view were explained in the description.

 Mcswell 01:40, 24 October 2006 (UTC)

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.

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. --Chetvorno^TALK 16:30, 29 December 2007 (UTC)

Any VDGG of about 27 cm diameter or larger could deliver a 1+ joule spark and is potentially lethal by itself. The spark from a 1 m sphere could be at > 1 MV and has sufficient total energy to cause cardiac arrest. (The max total energy scales as the cube of the diameter.) Even smaller spheres could be quite dangerous to pacemakers or other implanted electronic medical devices. See http://www.nuffieldfoundation.org/practical-physics/van-de-graaff-generator-safety for a lengthier discussion. Howard Landman (talk) 09:38, 15 May 2014 (UTC)

Graaf or Graaff?

The title and first line don't agree. Deizio talk 08:51, 21 January 2007 (UTC)

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)

I think it would, but not that page, but this. -- Harp 13:13, 21 March 2007 (UTC)

Oh, yeah. That'd be better. I'll just go ahead and add it.Slartibartfast1992 00:46, 26 March 2007 (UTC)

Hair

Why no mention/explanation of the hair-stnading-on-end phenomenon?

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. --Chetvorno^TALK 16:19, 29 December 2007 (UTC)

Applications

Sorry for removing the part about applications, I just had never heard of these applications and thought they were misconcieved extrapolations of it being a high voltage source and that other high voltage sources (which I've seen on accelerators where I study) are used for the purposes here stated. Sorry also about not just placing a tag as it is proper conduct here in WP. I got distracted and when I got back to this and found good sources found out someone had already done the revert I was about to do. I'll add a source to this application so that other people don't make my own mistake JunCTionS 22:58, 30 July 2008 (UTC)

One of the great things about Wikipedia is running into something you've never heard of; after having this occur scores of times, I'm now very cautious about deleting something I see only on the Wikipedia, even if its in a field I think I know pretty well. References are good. Mind you, there are crackpots about, too....which makes it more interesting. --Wtshymanski (talk) 13:16, 31 July 2008 (UTC)

Schematic View incorrect?

The image shows a positive charge at the top and negative charge on the bottom (and coming around on the wand-like object). However, the caption says that the lower roller is metal and upper roller is some sort of plastic (maybe acrylic).

Shouldn't the side with the metal roller be positive? (Edit note by AlexWillisson: I'm checking this against the book Homemade Lightning second edition by R.A. Ford) --AlexWillisson (talk) 03:23, 23 March 2009 (UTC)

Also, the image shows that a positive charge is created on the dome, but the text currently says "the sphere continues to accumulate negative charge". I traced the change from "positive" charge to this edit http://en.wikipedia.org/w/index.php?title=Van_de_Graaff_generator&diff=prev&oldid=261865989 . Currently there is definitely something technically wrong with the article, but I don't have the knowledge to fix it. -Lissa —Preceding unsigned comment added by 68.50.162.114 (talk) 02:21, 24 February 2010 (UTC)

The image is of a classic Van de Graaff generator, while the text describes a more modern one with a high voltage source. I agree that it's confusing. 84.197.178.75 (talk) 13:23, 8 March 2012 (UTC)

Answer: The charge depends on whether you are going by what it actually is or what Americans call it. In America, positive and negative charges are switched. — Preceding unsigned comment added by 71.231.99.146 (talk) 00:54, 8 February 2014 (UTC)

Eh? No they're not. The electron always carries a negative charge, and the proton a positive charge, regardless of whether you're in America or anywhere else.

What is different, is the direction of assumed current flow, but this is just a difference of convention that exists between physics and engineering. Physicists routinely use "positive current flow" -- from positive to negative -- whereas engineers more commonly use "electron flow" -- from negative to positive. This has nothing to do with nationality, but merely one of those artifacts from an earlier age (like the "QWERTY" keyboard) that has been retained by tradition, long after the original reason for it has been forgotten or become irrelevant. — Preceding unsigned comment added by 74.95.43.249 (talk) 00:38, 9 May 2015 (UTC)

No, there's no difference in terminology between physics and engineering. Both physicists and engineers use conventional current (the correct name for "positive current flow") unless they are specifically talking about the direction of "electron flow". --Chetvorno^TALK 04:24, 9 May 2015 (UTC)

answering the question

all your hair get negatively charged so negative charges attract eureka! you hair stands upFdkmx236 (talk) 19:36, 23 April 2010 (UTC)

 —Preceding unsigned comment added by Fdkmx236 (talk • contribs) 19:35, 23 April 2010 (UTC) 

contradiction in Description section.

As noted by AlexWillisson above, the illustration does not match the description in the text. The text describes a generator where the charge is provided by a high voltage source, the image is one charged by friction due to the different material of the rollers. Also, the legend with the picture is:

3) upper roller (metal)

..

6) lower roller (for example an acrylic glass)

But when you look at the picture file page [File:Van_de_graaf_generator.svg|File:Van de graaf generator.svg] (don't know how to link to such a page, just click the picture.) there it reads:

1. hollow metallic sphere (with positive charges)
2. electrode connected to the sphere, a brush ensures contact between the electrode and the belt
3. upper roller (for example in plexiglass)
4. side of the belt with positive charges
5. opposite side of the belt with negative charges
6. lower roller (metal)
7. lower electrode (ground)
8. spherical device with negative charges, used to discharge the main sphere
9. spark produced by the difference of potentials

And the three other languages agree with this. Basically, someone tried to match the text with the illustration, adding the numbers to the article, then maybe someone else noticed discrepancies and tried to fix them by altering the legend under the illustration, but it's still not correct. Seems the best thing to do is change the text so first a "statically charged" one like in the drawing is explained, with corresponding numbers, right charges etc.., and with the original legend under the picture. and describe the "electrically" charged one in the next paragraph, the one that currently reads:

Another method for building Van de Graaff generators is to use the triboelectric effect. The friction between the belt and the rollers, one of them now made of insulating material...

84.197.178.75 (talk) 14:34, 8 March 2012 (UTC)

I have noticed also this and tried to correct it, modifying the figure and the text in wikimedia commons. There are two possible systems, one with the plastic cylinder on top and the other with the plastic on the bottom. The positions of charges is different in both cases.

• If the plastic is on top (as in the real one I use to explain it to my students) this cylinder becomes positively charged and the belt goes down negatively charged. It attracts positive charges from the ground and goes up neutral (not with positive charges!) with negative charge in one side and positive in the other. When it reaches the top, the positive charge of the cylinder repels the ascending one and this goes to the outer shell.

• If the plastic is at the bottom, the cylinder becomes negatively charged (to keep signs consistent) and the belt ascends with a positive charge. When it reaches the top it attracts electrons from the outer shell (that becomes positively charged) and descends neutralized (positive on the inside, negative outside). At the bottom the plastic cylinder repels the electrons that go to the ground.

Here the two corresponding figures. I'll leave to you to select the more consistent versions across the different wikipedias

Version 1 Version 2 Gonfer00 (talk) 21:10, 30 May 2012 (UTC)

Edit war

Wikipedia:Administrators' noticeboard/Edit warring#User:Менде Фёдор reported by User:Guy Macon (Result: ) --Guy Macon (talk) 19:23, 10 June 2017 (UTC)

Charge on Belt

The figure showing the charges on the rubber belt is still not correct. For the acrylic roller being the one on the top, as shown in the figure, this roller will acquire a positive charge (as shown in the figure) due to the triboelectric effect. This will cause negative charge to get sprayed onto the outer surface of the belt as it passes below the top electrode sprayer (and thus the dome becomes positively charged). The belt thus descends with a strong negative charge on its outer surface, on the right (descending) side of the belt (assuming that the belt is turning clockwise, as shown in the figure). This charge is mainly removed by the electrode charge sprayer at the bottom, so that the charge on the outer surface of the belt is minimal on the ascending (left) side of the belt. The entire inner surface of the rubber belt will acquire a negative charge from the triboelectric effect, but the corresponding charge density is weak due to the large surface area of the belt (compared to the roller), and this charge thus plays no important role. More details may be found in the following reference: http://amasci.com/emotor/belt.html 2600:1700:12B0:2FC0:DD5:6AA9:1D5B:9722 (talk) 22:52, 14 March 2023 (UTC)