|WikiProject Physics||(Rated C-class, High-importance)|
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)
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 22.214.171.124 (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. 126.96.36.199 (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 188.8.131.52 (talk) 00:52, 7 April 2012 (UTC)
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.
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
Why is it not "van de Graaff"? Isn't this more consistent? Dysprosia 10:24, 24 April 2006 (UTC)
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 o contribs) .
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.
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)
The starting description talks about E1 and E2 electrodes. It would be easier to understand if the schematic view showed those electrodes as well.
Mcswell 01:40, 24 October 2006 (UTC)
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.
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)
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)
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: . Please tell me if it would be a good addition to the external links section. Slartibartfast1992 16:32, 10 February 2007 (UTC)
Why no mention/explanation of the hair-stnading-on-end phenomenon?
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)
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)
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?s=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 184.108.40.206 (talk) 02:21, 24 February 2010 (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 220.127.116.11 (talk) 00:54, 8 February 2014 (UTC)
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:
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:
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:
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.
Here the two corresponding figures. I'll leave to you to select the more consistent versions across the different wikipedias
popflock.com Resource: Administrators' noticeboard/Edit warring#User: reported by User:Guy Macon (Result: ) --Guy Macon (talk) 19:23, 10 June 2017 (UTC)