Physics & Physical Science Demos, Labs, & Projects for High School Teachers

Experiments with a van de Graaff Generator

Posted on: April 12, 2009


I now feel qualified to put something up on this post.  We played for two whole days in my physical science class, and the kids still want more.  Another day in my three physics classes, and I’m battle ready.

I began by showing the balloon on the bald teacher’s head and sticking it to the wall.  Trust me, nothing gets them going more than a mostly bald teacher trying to rub a balloon on his hair. Amazingly, there were quite a few students that had never seen a balloon charged up and stuck to a wall.

We then went to the standard acrylic/fur type of static charge, explaining how the charges separate.  I caused paper and bits of styrofoam to jump from the charge.

The van de graaff generator is exactly like those static creating devices, but it just keeps making more and more static.  Here are a few ideas I have either done or picked up on the internet.  One important note; I got all of the kids up and involved.  Some of them were scared, but after the girls charged up their hair without pain, the chickens were shamed into bravery.

Before doing each of these demonstrations, I ask the students what they think will happen:

1.  I take a bunch of holes from a paper punch and put them on top of the dome.  Then I turn the machine on and the holes fly up into the air.  The dome and paper, all having the same charge, repel each other.  The paper holes spray up in a fountain of white dots.

2.  I tape strips of paper to the dome.  The paper stands up and stays standing until the dome is discharged.  This is a good precursor to the hair thing.  They don’t expect the paper to stay up in the air when the machine is off.

3.   I use the grounding electrode to make the sparks jump really far.  Let the generator run until you hear the ozone crackling.  Then you get a great big spark.  I use this to build some tension and fear of the generator because I’m asking for volunteers to do the hair thing.

4.  Making hair stand up.  The student needs to stand on a plastic milk crate or something to insulate them from the floor.  One student wanted to try this standing on the ground.  I think he had sweaty feet, he said (and we heard) the discharge going through his feet into the floor.  I wish I could tell you how to know what kind of hair works best.  Really long hair is too heavy, really short hair is too stiff.  Hair color doesn’t seem to matter, although dark is easier to see than blond.  For some reason, the hair of the black girls worked best.  I’d love to post the pictures, but posting pictures of student’s is a no-no, at least without written permission.

5. Fluorescent light bulb lights up.  It does not need to come into contact with the dome, the spark jumping to the glass with light up the bulb.  We found that placing the bulb about 1 inch from the dome gave the best results.  Stand on a piece of wood or you will feel the shocks in your toes.

6.  We made a chain starting with one person charged up.  He touched the next person, but held on.  Now they both charged up and continued to another person.  If the person getting shocked was sitting in one of our desk/chair units, he or she got a constant stream of shocks to the legs and back side.

7.  Water bottle on top produces lightening like show.  I’m going to tell you to be careful with this one.  It works pretty well at first, but the massive sparking in the bottle actually burned through the bottom of the plastic bottle.  Once they started leaking, they wouldn’t charge up.  I had to use a different bottle for each class.  More importantly, the bottle kept the charge.  Just holding the bottle and moving it around gave a constant stream of rather painful shocks.  At one point I was holding the grounding rod and the bottle.  I touched where the bottle was leaking through the bottom and I got an extremely nasty jolt across one arm to the other.  Be careful with this one.

8.  A balloon placed near the dome is first attracted, then when it touches the dome, the charge is conducted and it is repelled.  The charge leaks off and this repeats over and over again.  I used this to lead into Coulomb’s Law and the force due to the electric charge.  Again, you will want to stand on something to insulate you or you will have toe sparks.

Here are a few demonstrations that I haven’t yet tried:

  • Mini pie tins stacked on top fly away one at a time – the pie tins I tried were too big.
  • Soap bubbles are repelled as they get near the dome.

Any more?

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31 Responses to "Experiments with a van de Graaff Generator"

Just a short note about #2 (strips of paper) – I don’t know how flexible your paper is, but I use streamers…. while the strips are still repelling each other, after the VDG is turned off, send a student to touch one of the strips of paper. The others around it will be attracted and will look like they are “reaching” for the student! Very fun, and Little-Shop-of-Horrors-ish!

Thanks for the post! I’ll have to try the paper punch holes next year….

One thing I like to do is tape the end of a few pieces of yarn down on the top of the VG and then place a pie tin on top as a hat with a face painted on the front. Turn it on and the “hat” flys off while the “hair” stands up.

Dear friend ,
These types of motion pictures are required to tezhc class XII CBSE physics

geetha ramesh

I am a student who is interested in doing a science fair project that is related to a van de graaff generator. I need to make a safe Van De Graaff generator or else I will be permitted to do the project.
Do you have any suggestions on:

what thesis i might use
what i might do as an experiment
how to make a safe van de graaff generator

Most importantly how I can make a home made one if I am not an electronics expert and I know almost nothing about electronics. I am going to need step by step instructions, a kit, or what?

Thank You,
Jack

Jack,
This is a really cool project, if you can get some help, go for it. Go to http://www.instructables.com and do a search on van de graaff, you will get several sets of instructions.

The wiring is only a motor. I would use a DC motor because varying the voltage changes the speed. The charge you build up on the generator isn’t likely to be enough to do any damage. The one I have at school is 400,000 volts, it can sting, but it doesn’t hurt anything. You won’t likely get that much voltage out of yours. We can barely make hair stand on end with 400,000 volts.

As for your hypothesis, do some research on “static electricity” and the van de graaff and see what kind of effects you can create. Maybe – “Can you light a bulb with static electricity?”

Good luck.

Scott

Thank very much for your advice Scott. I have decided to make my hypothese about Static Electricity like you recomended. I would also like to buy a real Van de Graaff generator in addition to the one I will build. I found two websites. One describes how to build a Van de Graaff generator at home with step by step intructions. The other is from a store and has accesories.
this is the tutorial how to make it:

http://scitoys.com/scitoys/scitoys/electro/electro6.html

this is the website of where to buy it:

http://www.grabcart.com/product/vg/pcgames/unbeatablesaleamed3380/Ginsberg-Scientific-7-501-14-Van-de-Graff-Generator-With-Accessories

If you know of a different Van de Graaff generator that is better or cheaper please let me know.
Also please tell me what you think of the Van de Graaf generator that I will make. Please tell me if you know of a better one that I can make.

Thank You,
Jack

I like the plans for the generator, that’s pretty simple, but it should work just fine. A larger dome holds more charge, and round is optimal. So if it works with a soda can, you might be able to improve upon the design by using something larger and rounder in its place.

My department purchases our lab equipment from Carolina Biological Supply. They have good stuff, however it is much more expensive. I use the 350,000 volt model.

http://www.carolina.com/p2p/endecaSearch.do?keyword=van+de+graaff&Search.x=0&Search.y=0

The one you are looking to buy seems fine, but it doesn’t list the voltage it generates, which makes it hard to compare. It seems perfect for your use, although I’m not sure what you will do with it after the science fair.

Thanks so much for all your help but I’m still stuck with one key issue?… What is my Hypothesis for my Science Fair project. I now have the experiment and procedure down cold but I still need a hypothesis. What am I trying to prove? I am really having trouble coming up with a hypothesis

Do you have any suggestions?
Any questions I might ask about static electricity or something that relates to a Van De Graff generator?

Thank for all your help,
Jack

Jack,
I’m not exactly sure how you can have an experiment without a hypothesis. In simple words, what are you doing, demonstrating, or trying to show with your experiment?

I want to build a home-made van de graff generator. Can you tell me what parts I need and direct me to where to buy them.

P.S. Where can I find
* Two pieces of 3/4 inch PVC plumbing pipe, each about 2 or 3 inches long
* One 3/4 inch PVC coupler
* One 3/4 inch PVC T connector
(please direct me to sites where I can buy these materials)

David,
The supplies you are looking for are available at Home Depot, Lowes, or any other building supply house. They should only cost you a few dollars. You might also ask a few handy people if they have the pipe, since you might end up buying an eight foot section when you only need a few inches.

Thank You my science Fair project is going well. Just a question… Is it dangourous to put a light bulb in a static spark. What will happen.

When you say static spark, I’m assuming we are still talking about your Van de Graaff generator. No, it’s not dangerous. You probably won’t get anything to happen with a regular bulb. An incandescent bulb lights up because the wire in the bulb glows white hot. Try a fluorescent bulb, if you have enough voltage, it will light up. Those bulbs light because the gases in the tube are excited by an electric charge. I show the fluorescent bulb every year as part of my Van de Graaff demonstration.

Please send along pictures or a link to pictures from your project, I’d love to see how it turned out.

hello, my son is finalizing his conclusion to a hypothesis for a science fiar project, using a home-made van de graff.

exactly WHY do some materials NOT produce a spark like our finger does? we think it’s because of the rough surface area (like a feather) which disperses the electrons faster.

any ideas?

We (people) conduct electricity, so the electrons will flow from the generator to you. You feel a spark because the charge can find a path to ground. A feather doesn’t conduct electricity, so it has nowhere to go. The Van de Graaff builds up an electric charge and it is looking to get rid of that charge. We get close and give it a path through our body and possibly down to the floor. However, sometimes we just share the charge with the generator, its charge becomes less and your charge becomes greater, but the key is that the two charges become equal.

To test the idea of a difference in voltage, take a number of items that do not conduct electricity, like a wooden dowel or a ceramic object. There shouldn’t be a shock to those items because they are insulators. Your best demonstration of the sparks is if you make a grounding rod by connecting a metal object to an electrical ground. Now you have a large difference in voltage between the dome of the generator and the grounding rod. You should then see the sparks jump.

Did that help?

Built a few generators for schools. Belting was biggest problem till I tried survery rubbon It works very good

Hi Scott

For school, our assignment is to touch a van der graffe and NOT recieve a shock. I know that insulators (such as plastic and wood), dont allow the conducting of electricity. So from that, does that mean that if i stand on a piece of wood, and touch a negatively charged van der graffe, i won’t recieve a shock?

Or am i supposed to wear metal shoes, touch the negatively charged vandergraffe and allow the charge to be conducted to the ground, so that I don’t receieve a charge?

i’m confused, please help .

-Suzy

Hi Suzy, I hate to give away another teacher’s assignment. Here is a hint, but not the total answer:

As long as there is a sufficient voltage differential, you are going to get a shock. The only way to not get a shock is for you to be at the same potential as the machine. The question becomes – How can you be at and stay at the same potential as the generator?

Hi Scott,

Don’t worry, I understand. If you don’t mind, I just want to clrify some of my doubts. Okay so, since I do have to be the same charge as the van der graffe (which is negatively charged), I have to make myself negatively charged as well (such as combing my hair, and rubbing my feet against the floor), but I do know that since I am touching the floor, there is a chance for the electrons to leave me (since i am grounded) – that IS what grounded means right ?
So since I will be grounded, I have to stand on wood, which will prevent the electrons from travelling to the ground so that I will stay negatively charged and therefore, won’t recieve the shock. Am I on the right track or am I getting more confused than before.

-Suzy

You are on the right track about the grounding. But you can’t comb fast enough to compete with the generator.

Hi Scott,

Now that I think about it, I don’t think I can’t have more of a negative chrage (than the van der graffe) , no matter what i do (so i might as well stay neutral).
Therefore, I have decided to stand on a piece of wood, so that the electrons wont be grounded – even though the electrons are entering me, they don’t have a way of getting out, so I don’t receive the shock. I think I’m starting to understand.

Hopefully I’m getting close.

Suzy, I think you are doing great. Why not watch this video and see if it doesn’t put the finishing touches on your learning experience.

thank-you so much for the help Scott! I think I finally get it!

Thanks for a great post on VdG generators!
I have a question about the dome, is it really necessary for it to be round, I mean can I use a capacitor instead? What is the point of having it spheric?
I think I’ll build one, but as light as possible, to make it stick to the wall like a balloon. Is this even possible?
Grateful for answers
Erik

Okay Erik, let’s take your questions one at a time but out of order.

To make this thing stick to the wall, not real likely. A balloon weights next to nothing. There is no way you are going to put the motor and brushes and sphere together and make it light enough for the static charge to hold it up. Let me rephrase that. It probably can be done given enough money and effort. You can work backwards using Coulomb’s law to figure out the force you can generate from charges and see how much of a charge is required to lift a 20 lb generator. Then when the charge drops, it falls and breaks. I’d rather spend the time and money making a good large generator.

As for the shape, a sphere allows for maximum stored charge, it’s the most efficient shape. Sharp edges allow the charge to leak off. A charge dissapators on the trailing edge of airplane wings (or whatever the aerospace industry calls them) are pointed to allow the charge to leak off – no surface area to store the charge. If you make the top a cube, charge will leak off the corners.

I suppose you could use a large capacitor like the type used in car stereos, but where’s the fun in that. Then it would be a Leyden Jar and not a van de graffe generator.

I’ve seen designs using very large metal kitchen bowls. The key is the dome, the bigger the dome, the more charge it stores, the more fun you can have.

My Friend & I are doing a Van De Graaff generator for our science fair. We were going to attempt to make it run on hydro power but we believe that is a little Dangerous. What would be some safer but not too predictible ideas using a VdG Generator?

You could hook it up to a treadmill or maybe a hamster wheel. How about a windmill? None of this really makes any sense, the Van de Graaff is more of a demonstrator than a practical device. It’s really just automating the process of dragging your stocking feet on the carpet and shocking your brother on the ear. Fun, yes. Practical, no so much.

On Wed, Dec 12, 2012 at 8:37 PM, Physics & Physical Science Demos, Labs, & Projects for High School Teachers

Ok so what are some other alternatives to this because we really want to use physics in our experiment

Put a thumb tax on a piece of clay, pin side out. Then put clay with tac/pin at equator of Generator. Hold a birthday candle close to pin and electrons coming off pin will blow out candle! By the way, Pie tins work well too.

Hi, I’m a physics student in high school and in our last introductory physics lesson our teacher showed us a few thighs with a VDG generator. The one I’m most interested in is the flourescent tube which lights up when held an inch or so away from the sphere. Our class noticed that the tube only really lit up when held away from the generator, and not touching the charged sphere. My teacher wasn’t able to explain this and I was wondering if you might have the answer? Thanks for your help.

Hi Eleanor,
I believe the reason it lights is because of an inductive charge provided by the VDG. If you were to open one of those fluorescent tubes up (don’t), you would not see a wire between the two sides. The tube has electrodes at each end, this creates a charge field which causes the gases to jump up and then fall from their excited levels, causing light to be emitted. The inductive charge of the VDG does the exact same thing. When you touch the tube to the generator, the tube is at the same level as the device but the other end isn’t grounded, so there is not a voltage difference. There is a lot going on there, but not beyond what you can understand.

If you want to do some research and look really smart, look up the Balmer Series, which is what causes light to be emitted from a star. The principle is the same here. You can also look up induction and inductive charges.

Lastly, this is all off the top of my head, I didn’t research it, so if I’m off on any of this, somebody will hopefully jump in and correct me.

What do you think? Your opinion matters, leave a reply.

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