What is Van de graaff: Definition and 56 Discussions

Robert Jemison Van de Graaff (December 20, 1901 – January 16, 1967) was an American physicist, noted for his design and construction of high-voltage Van de Graaff generators. The bulk of his career was spent in the Massachusetts Institute of Technology.

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  1. J

    Electrical Build or Buy a Van de Graaff generator?

    Wonder how much skill is needed?
  2. gregory112

    Troubleshooting a homemade Van de Graaff machine

    I'm trying to build a Van de Graaff generator, but it does not generate any charges. The problem is, I don't know which part is accidentally shorted, or grounded. I use both PVC pipes for the top and bottom rollers. The belt is neoprene rubber, 1mm thick. The rollers are bolted on aluminum...
  3. archaic

    Maximum electric field at the surface of a Van de Graaff generator

    I know that the potential of the sphere at its surface is ##V(a)=kQ/a##, and the electric field generated by it is ##E(a)=kQ/a^2##, which gives me ##V(a)=aE(a)##. When the electric field at the surface is as in the question, we have...
  4. A

    Ground for a Van de Graaff Generator?

    I attached a jpeg of a Van De Graaff generator off the web. Is the point in the photo the Van De Graaff ground? Suppose I have a wire coming out of that slot instead of a discharging sphere, would that hole still be the Van De Graaff ground?
  5. C

    Electrical Decided to make a Van De Graaff generator

    Hi, I recently decided to make a Van De Graaff generator and I have a question regarding the top load sphere. I managed to get myself a very nice 60cm-diameter stainless steel polished sphere. Before I start cutting up the bottom part so to make room for the top roller with the collection comb...
  6. G

    Let current from a Van de Graff generator flow through you

    Hi. I have two questions about the following video with a 200'000 V Van de Graaff generator: At 5:57 he touches ground, apparently feeling nothing. He explains this with a very low current and proceeds that the current from a 120 V outlet is high and might kill you. But with ##I=U/R## and...
  7. T

    Small & Lightweight High Voltage Power Sources: Ideas?

    << Mentor Note -- thread moved to the Sci-Fi writing forum after starting in the technical forums >> Hey folks, I'm interested in the feasibility of providing high DC voltages (~kV) in a physically small and low mass package (~grams). The power source does not actually need to be very energy...
  8. A

    True output voltage on a Van De Graaff generator?

    Greetings, How do you know what the true output voltage on a Van De Graaff generator is? Can it be measured? If a manufacturer advertises it as having an output voltage of 100,000 Volts, is this an idealistic, classroom quote or the true quote they have actually measured? If the output voltage...
  9. A

    Measuring Charge on a Van De Graaff Generator: Methods and Obstacles

    Greetings, Does anyone know of a way to measure the actual charge of a Van De Graaff generator, in Coloumbs? One way I thought might be to measure the voltage potential around the generator, and calculate the charge from V = kQ/r, but would this work in just regular air? What obstacles would...
  10. eigenmax

    External-excitation Van de Graaff polarities

    My question regards the polarities of the excitation supply and terminal in an external-excitation VDG. As you all probably know, external excitation VDGs use a voltage supply (usually 5,000-10,000V) to influence the charge on the lower pulley, instead of just relying on frictional contact to...
  11. A

    Quick Question on Van de Graaff Particle Accelerators

    Hi everyone. Just a small, quick question I have: Can negative ions be accelerated by a Van de Graaff particle accelerator? My initial reaction is no, because the terminal (the sphere with the charges allocated on the outside) is positive, which means negative ions would be attracted and not...
  12. Blackhawk4560

    Can a capacitor increase voltage beyond initial charge?

    Question: If you charge a capacitor circuit and then separate the capacitor, does voltage increase beyond the initial source? It seams counter intuitive that if you plug a 9 Volt battery into two metal plates and pull the plates apart that you'll get massive voltage spikes, but that's what the...
  13. I

    I Leyden Jars increase spark length?

    Good Evening/Morning/Afternoon Everyone, Question: Why is it that demonstrations of Van de Graff generators use Leyden Jars in series to get bigger sparks? If a spark gap's size determined by voltage, and Leyden jars are simply to be treated as capacitors which wouldn't increase voltage, why...
  14. S

    How to find the mass of a pith ball using electric forces?

    Homework Statement A pith ball is charged by contact with a Van De Graaff machine, and is repelled away from the dome. It remains at its location. Using the chart given, what is the mass of the pith ball? Distance between centre of generator and pith ball...
  15. weezy

    Why is current in Van De Graaff generator so low?

    I know that current depends on the impedance and potential difference b/w two points so why does a van de graaff generator pose no serious shock hazard i.e. why the extremely low current between the generator and ground? As seen in this video demonstration the instructor safely touches the...
  16. G

    How does this specific Van de Graaff generator work?

    Hi. I have access to following Leybold Van de Graaff generator: The instructions and data sheet can be found here, but they don't give much insight. I have found different working principles of VdG generators. Some need the rising and falling sides of the belt to be closely together from top...
  17. Aldo Biko

    The force between charged and neutral object

    Homework Statement I did a lab involving Van de Graaff generator. Basically, below the charged sphere, I put a neutral sphere on a scale and measure the difference in mass which then I can calculate the force acting on the neutral sphere. I repeated the experiment with different distance. What...
  18. A

    Problems Building a Van De Graaff Generator

    I have been trying to build a small Van de Graaff generator based on the designs found here: http://rimstar.org/equip/build_make_van_de_graaff.htm Unfortunately I haven't been having much luck. How can I improve it...
  19. electricnoob

    Confused about electrostatic voltage and DC voltage

    Hi everyone, I am a little confused conceptually about electrostatic voltage and DC voltage. I did my bachelors in biochemistry (where I’m working today), I’m learning/relearning physics as a hobby. I did well in high school physics and first year physics but I’m afraid I’ve forgotten most of...
  20. D

    Charge on van de graaff generator

    Is there any easy way to determine the charge on a van de graaff generator based on the voltage?
  21. mattbeatlefreak

    How to Calculate Force for Van de Graaff Generator | 70-Year Old Challenge

    Homework Statement A fellow scientist heard that a Van de Graaff generator built 70 years ago could collect 5.0 C of charge on its dome, which had a radius of 1.1 m, and has challenged you to do the same. You plan to use the same dome with the same radius and the belt you plan to use is 200 mm...
  22. S

    Exploring the Possibilities of Spark Generation with a Van De Graaff Generator

    If you run a wire from the outside surface of the dome to the inside of the same dome, would it be possible to make a spark to the inside surface of the same dome?
  23. J

    Understanding Van de Graaff Questions: Explaining the Lack of Arc Formation

    Hi all, I've been playing with a van de graaff this week. As I'm sure you know, pointing a nail at someone with their hair raised by the machine will result in the hair immediately sticking back down. I can easily imagine electrons flying off of the tip of the nail and into the hair of the...
  24. 655piano

    Electrical Fixing Warped Hemispheres for a DIY Van De Graaff Generator

    Ok, so I'm building a Van De Graaff generator from parts I've been collecting for some time now. I have 2 hemispherical bowls that were supposed to line up perfectly to make the ball at the top. shipping has warped them just the slightest bit. I'm wondering if this will produce coronal leakage...
  25. A

    Van de graaff generator as a current source

    I know that van de graaff generator is a high voltage generator, i was wondering though if we can use it as a current source, if we get any resistor, connect the negative terminal to the generator "if the generator generates negative charge " then ground the positive terminal, then any charge...
  26. S

    Van de Graaff Generator : Limiting factor on Voltage

    Many sources talk about the field inensity (and therefore arcing/breakdown) on the outside of the dome as a limiting factor on the highest voltage that can be possibly reached on a VDG machine. There are also references to possible dielectric breakdown along the belt itself. I am wondering if...
  27. S

    Why do Van de Graaff generators produce such low current?

    I'm currently in a program to be a physics teacher and for an upcoming mock lesson plan I am going to show the scene from Jurassic Park where the kid gets blasted off the electric fence and talk about if it is realistic. To supplement my discussion I'll be using a Van de Graaff generator to...
  28. C

    Simple Van de Graaff Generator Problem

    My area of concern is C) and if I am correct in assuming it is like Faradays cage, but I am new to all this so I also put down A and B also. If you charge up a Van de Graaff Generator and then bring an identical but uncharged hollow conducting sphere near it, without letting the two spheres...
  29. A

    Van de Graaff generator questions?

    Hello~ I've got a confusing question; "If a Van de Graaff generator is charged to 50,000 volts, how much energy does it take to add an additional electron to the charge on the sphere?" (The charge of an electron is given as -1.6 x 10^{-19}C) My answer: (50,000 V)( -1.6 x 10^{-19}C) = 8.0 x...
  30. T

    Van de Graaff Generator - Shock vs. No Shock?

    Hello all, I have a quick, albeit probably ignorant (forgive me) question generated by (bu dum) observations of a van de graaff generator. In particular, two distinct scenarios caused me to question what was going on. Scenario 1 – I’m standing on a plastic stool, with one hand on the...
  31. A

    Understanding Franklin's Wheel: A Van de Graaff Experiment

    Hey guys, I'm new to this forum so I'm sorry if I posted in the wrong thread. So we did these experiments with van de graaff and I almost understood all of them except what seems to be "Franklin's wheel" experiment. I know for one thing that the air near the sharp points are ionized but I don't...
  32. B

    Building a Van de Graaff Generator: Tips and Considerations

    I am building one. Not for school but for personal reasons. Is anyone here familiar or has built one before? I have some questions such as can the collector be any size? The maxium voltage of the collector is generally .8(70000r) with r being the radius of the collector. I was wondering if...
  33. D

    Why is my body so sensitive to a van de graaff generator

    my husband has a van de Graaff generator and one day he decided to bring it out and show me since i had never seen one. well after about 5 minutes of it running i could not even be in the same room as it while it was running because it caused me physical pain. now i want to know why did this...
  34. O

    What happen to a metal bar near a Van de Graaff?

    When I place a metal bar near a Van de Graaff, which generate hugh amount of positive charges on its surface, if I hold it for a period of time, will it be possible to magnetize this metal bar? what happen to its internal molecula structure? Does anyone have any suggestions? Thanks in advance...
  35. C

    Confusion: Van de Graaff generator

    My physics book explains a van de Graaff in this way: A small conducting sphere of radius a and carrying charge q is located inside a larger shell of radius b that carries charge Q. A conducting path is momentarily established between the two conductors, and the charge q then moves entirely to...
  36. J

    Van de graaff without insulation?

    Hi, Why do all the designs for a Van de graaff generator have a insulated belt that delivers charge? Couldn't I just connect the negative terminal of a battery to the inside and get the same effect? Van de graaf from wikipedia http://en.wikipedia.org/wiki/File:Van_de_graaf_generator.svg
  37. D

    Can You Charge a Polarized Capacitor with a Van de Graaff Generator?

    I'm trying to charge a capacitor with a van de graaff generator. Where do I put the positive and negative nodes on a generator like this http://www.chrisbrenton.org/wp-content/uploads/2009/07/van-de-graff.jpg
  38. D

    Help with Van de Graaff Generator & PVC Pipe Setup

    Homework Statement I have to make a van de graaff generator for my physics class. Homework Equations The Attempt at a Solution I put it together and it doesn't work at all. Please help. Is the reason it isn't working is that i don't have a glass tube or something else? Homework Statement...
  39. J

    Van de graaff accelerator - do-able?

    van de graaff accelerator -- do-able? (posted in the wrong forum -- apologies)
  40. U

    Where does charge go in this van de Graaff generator?

    Sorry, I had a long post that just got eaten by my computer so I am having to re-type my question. It will need to be brief: Here is an example of a van de Graaff generator: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/vandeg.html It notes that the bottom brush is "given a positive...
  41. C

    Van de Graaff + Leyden jar a dangerous demo?

    Hello all, In my first high school physics class my teacher performed an incredible demo that has stuck in my mind ever since. After playing around with a Van de Graaff generator a bit he whipped out one of those homemade plastic bottle and aluminum foil Leyden jars and charged it up using...
  42. D

    Van de Graaff Generator in a Vacuum

    So I am in an intro E&M class and the topic of Van de Grraaff generators came up. The instructor said that when there is enough charge on the surface then there is corona discharge. But what would happen if the generator was in a vacuum? Then there would be no corona created. So would the amount...
  43. blainiac

    Accelerating ions using Van de Graaff help

    First, let me say hello to everyone on the forums! A friend and I have converted a 36" CRT television into a HV source using its flyback transformer. We discharged the tube before taking anything else apart. We have the HV source attached to a thin wire, which causes the air around it to...
  44. G

    Electric force of Van de Graaff generator problem.

    A Van de Graaff generator is charged so that a proton at its surface accelerates radially outward at 1.45 10^12 m/s2. Find the following. (a) the magnitude of the electric force on the proton at that instant magnitude (b) the magnitude and direction of the electric field at the surface of...
  45. R

    Attracting small splinters of glass with a Van de Graaff generator

    Hello, I work for a container factory where re-used bottles have a lot of tiny glass splinters. Inspired by the standard experiment of picking up glass splinters using a comb, I thought I could insert a charged rod into a bottle to attract little splinters towards it. To get similar voltages...
  46. G

    Van de Graaff generator? adding a electron?

    Van de Graaff generator? adding a electron?? Homework Statement A)If a Van de Graaff generator is charged to 5,000 volts, how much energy does it take to add and additional electron to the charge on the sphere? If the charge of an electron is -1.6 x 10 ^-19... B) How would the voltage...
  47. Artlav

    Debugging Van De Graaff generator

    I'm trying to build a simple Van De Graaff generator, for the first time. The problem is quite obvious - the current generated is zero. Can somebody help to find what is wrong? The column is a typical sewer pipe, axles are aluminum bars, electric screwdriver acts for motor. The upper...
  48. M

    Van de Graaff & electric force?

    Homework Statement A Van de Graaff generator is charged so that the electric field exerted at the top surface is 2.0× 10^6 N/C directed upwards. Find the a) the electric force exerted on a styrofoam peanut (q= 0.025μC) released at its surface, b) the gravitational force on the peanut, c) its...
  49. S

    Fusion or not with Van De Graaff machine and very high voltage

    Using a Van De Graaff (VDG) machine, we can easily generate million-volt high voltage. The high potential difference can be generated effectively with minimum energy supplied to the machine. The larger the volume of the machine would be, the higher the voltage could get. However, stability would...
  50. S

    Getting higher potential difference with Van De Graaff machines

    Using a Van De Graaff (VDG) machine, we can easily generate million-volt high voltage. The high potential difference can be generated effectively with minimum energy supplied to the machine. The larger the volume of the machine would be, the higher the voltage could get. However, stability...