van de graaff machine experiments

How Van de Graaff Generators Work

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Experiments

There are millions of interesting experiments you can perform with your new Van de Graaff generator, but I will concentrate on the "hair raising" one. Have the lucky participant stand on top of an insulated surface (a Rubbermaid container top works well). It is critical for the person to be insulated from ground. If the charge cannot build up on the person, his/her hair will not stand up. Now, have the person put a hand on the sphere. Turn on the Van de Graaff generator and watch it go!

When the Van de Graaff generator starts charging, it transfers the charge to the person who is touching it. Since the person's hair follicles are getting charged to the same potential, they try to repel each other. This is why the hair actually stands up. It would not make a difference if the polarity of the Van de Graaff generator were reversed. As long as the person is insulated, the charge will build up (assuming, of course, that the hair is clean and dry).

My Van de Graaff generator will create sparks about 10 to 12 inches in length. I like to charge myself on it and point at the aluminum blinds on the window. The charge (electronic wind) will cause the blinds to move. I can do this from about 8 feet away with ease. Soap bubbles are also interesting to play with around the Van de Graaff generator. They initially are attracted to the Van de Graaff generator and float toward it; once they become charged by the Van de Graaff generator, they float away due to repulsion. There are multitudes of fun things you can do with your Van de Graaff generator. Use your imagination!

For more information, check out the links below!

If your Van de Graaff generator does not seem to be charging properly, make sure that it is clean. Avoid oils or debris. You can also use a hair dryer on it to remove any moisture. I go through this ritual every time I want to use my Van de Graaff generator. You will be amazed at the difference it can make. You may want to turn off all of the lights and run the Van de Graaff generator in the dark. You will see bluish-purple sparks shooting out where ever you have leakage. Try to eliminate the leakage with tape, epoxy or silicon. It may even take combinations of the three, but it will be worth your while to do so.

Accelerate!

Demonstrations

Van de Graaff generator

See the show
Full show video
Sample scripts
Hydrogen balloon
Beach ball accelerator
Plasma ball
Cathode ray tube
Electrical resistance
Liquid nitrogen
Superconductivity
Beach ball collider
Cloud chamber
Curriculum links

The Van de Graaff generator is a classroom classic with a surprising heritage in cutting-edge particle physics. As well as making your hair stand on end, these machines were used to accelerate particles through millions of volts.

1 × Van de Graaff generator 1 × electrically-insulating stool Some confetti, or aluminium foil, or foil cake trays

The demonstration

This demonstration involves high voltages, and so it should never be done by anyone with a pacemaker or other internal electrical device, or who thinks they might be pregnant.

The first part of this demo requires a volunteer from the audience. It works best on someone with long, light-coloured hair free from ties and styling products: light hair is often thinner, which means it will stand up more easily, and is also easier to see. Don’t pick on an individual (they might be pregnant, or just shy!), but if you could encourage someone fitting that description that gives you the best chance of success.

Give your volunteer a round of applause and find out their name. Check that they aren’t wearing any metal jewelry etc, and ask that they remove it if so. Put it safely to one side.
Get the volunteer to stand on an electrically-insulating stool. Place one hand on top of the generator dome, and get them to hold out their other hand flat. In this, place some confetti, pieces of aluminium foil, or cake tins. If you have a suitable light, dim the main lights and illuminate their head from behind to emphasise the forthcoming hairdo.
Check they’re feeling OK, turn on the generator, and stand back. The only thing they need to do is not to take their hand from the dome and, should they do so, not try to replace it (or they’ll get a shock!). Make sure the earthed globe is a long way from the main one to avoid shocking the volunteer too.
The objects in their hand will leap out and, by the time that’s finished, their hair should be standing up pretty nicely. Get them to shake their head around a bit to encourage this.
Get the volunteer to take their hand off the dome, and jump down with both feet, and give them a round of applause!

Having shown the amusing effect of high voltage on a person, we can now explore the limitations of these devices as particle accelerators. The problem is sparks, and we can use the sparks to work out the voltage to which we charged up our hapless volunteer!

If you haven’t already, dim the lights.
Take the grounded sphere and place it near the dome of the Van de Graaff generator. When you get within a few centimetres, a spark should leap across with a crack. Do this a few times from different angles to show the audience.

Vital statistics

breakdown voltage of air: 30,000 V/cm

highest-voltage Van de Graaff: 25.5 MV

length of spark from Van de Graaff LHC: 7 TV ÷ 30 kV/cm = 2300 km

How it works

The rubber belt inside the Van de Graaff generator runs between two rollers made of different materials, causing electrons to transfer from one roller to the rubber, and from the rubber onto the other roller, by the triboelectric effect. Brushes at the top and bottom provide a source and sink for these charges, and the top brush is electrically connected to the Van de Graaff’s dome and so the charge will spread out across the dome.

This accumulated charge would like to distribute itself over as large a volume as possible, and so it will also spread out across anything you connect to the metal dome, including your volunteer. The reason it’s important to stand them on something electrically-insulating is that the charge would like even more to spread out over the whole Earth, and connecting them to that will both massively reduce the effect, and also cause an electric shock as the current flows from the Van de Graaff to earth through its unfortunate human intermediary.

When insulated, the build-up of charge on the volunteer causes forces light objects to spread out as far as possible too, causing the confetti or foil to leap from their hand and then causing the individual hairs on their head to stand up. When they jump off the stool, the charge immediately flows to earth and their hair will immediately return to normal.

To work out the voltage of the Van de Graaff generator, and thus the voltage on our volunteer, we can use the length of the sparks in combination with the breakdown voltage of air—the voltage required to cause air to dissociate into ions and become conductive. This voltage is about 30,000 V/cm for dry air (hot, humid or lower-pressure air will tend to spark more easily). Sparks from the Van de Graaff are typically a few centimetres long, giving a voltage between 50,000 and 150,000 V.

Their propensity to generate sparks is the fundamental limitation of Van de Graaff accelerators, or indeed any accelerator design based on a large, static voltage. Those used for research managed to get up to over 20 MV by clever use of insulating materials, right down to careful choice of the gas in which the generator sits to minimise the chance of sparks. A Van de Graaff can thus be used to accelerate particles up to reasonably high energies: moving an electron through 1 V gains it an energy of 1 eV, so energies of over 20 MeV are achievable by this method (and more if accelerating nuclei with greater than a single electron charge).

However, modern particle physics has gone some way beyond this: the Large Hadron Collider will ultimately use beams which have 7 TeV of energy each: equivalent to accelerating a proton through 7,000,000,000,000 V. If we divide that by the breakdown voltage of air, we can work out the length of a spark we might get from an LHC employing a single, giant Van de Graaff generator to accelerate its particles. We get 2,300 km: easily enough to stretch, for example, from Switzerland to anywhere in the UK.

HowStuffWorks: How Van de Graaff generators work
Google Answers: high voltage arcing distances
Wikipedia: Van de Graaff generator

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Note: All electrostatic demos work better on cold, dry days.

a. In this classic demonstration, the professor or a student volunteer stands on the insulated base and places his/her hand on the sphere of the generator. An assistant turns the generator on, and the demonstrator's hair stands on end. The demonstrator should have a key or other pointed object concealed on his person to hold up and spray off the excess charge when the demonstration is over. A similar effect can by demonstrated by placing a wig on the sphere, or by connecting the sphere to a paper plume. The electric flier shown below will spin by spraying off charge when connected to the sphere.

b. Two Van de Graaffs are provided, one of which charges its sphere positive, and the other negative. When both are turned on, they will spark to each other over 8 -12" distance. However, if a small point is placed on one sphere, aimed in any direction, even at the other sphere, no sparks will jump, because the point dissipates the charge into the air preventing the potential from building up.

c. When the pear-shaped metal sphere is charged by touching it to the Van de Graaff, a larger charge can be removed from the narrow end than from the fat end. The amount of charge is tested by the deflection of an electroscope. To produce a noticeable effect this demonstration must be done carefully.
	d. charge is on the outside of a conductor. Several demonstrations of these effects are described in
e. . A string connected between an electrostatic generator and an electroscope will not conduct charge, but a metal wire will.

f. . Smoke blown into a tube (from a cigarette) rapidly disappears when the electrodes on the ends of the tube are connected to the generator.
	g. " " A paper cup full of puffed wheat or small Styrofoam chips placed on top of the generator produces a spectacular effect. Bring your own puffed wheat.

Click on the images below to see movies

Van De Graaff Generator Wonders

Activity length, 20-40 mins., electricity forces and motion, activity type, discrepant event (demonstration only).

Most people have seen a Van de Graaff generator before at a science centre or on TV. You know that it makes peoples' hair stand on end, but do you actually know how it works?

Van de Graaff experiments are all based on the fact that like charges repel.

A Van de Graaff generator pulls electrons from the Earth, moves them along a belt and stores them on the large sphere. These electrons repel each other and try to get as far away from each other as possible, spreading out on the surface of the sphere. The Earth has lots of room for electrons to spread out upon, so electrons will take any available path back to the ground.

The grounding rod is a smaller sphere, attached by a wire to the Earth. It provides a convenient path for electrons to move to the ground. If we bring the grounding rod close enough to the large sphere, the electrons rip through the air molecules in order to jump onto the grounding rod, creating a spark and crackling noise.

When a fluorescent light tube approaches the negatively charged generator, the electrons on the generator flow through the tube and the person holding it. Flowing electrons result in an electrical current, lighting up the light tube. It doesn't take very much current to light a fluorescent bulb!

Putting Styrofoam peanuts or confetti on top of the Van de Graaff generator can create a cool trick. The electrons that collect on the sphere spread out into the Styrofoam peanuts and confetti, making the little, light objects negatively charged. When the negative charges on the peanuts repel the negative charges on the generator, the peanuts push off the sphere.

When a student puts a hand on the sphere, the electrons will spread out onto that person as they repel from the other electrons. They are most obvious in a person's hair because the like charges of the electrons repel each other and cause the hairs to stand up and spread away from each other. As long as the person is standing on an insulated platform, the electrons will not be able to travel down to the ground and their hair will remain standing up.

Explain how static charge causes materials to attract or repel each other.

Per Class or Group: A Van de Graaff Generator (available at Arbor Scientific ) a plastic stool Styrofoam peanuts (or confetti) metal pie pan a mirror

Key Questions

Where are the electrons?
What is making your hair stand on end?
Why doesn’t the hair come down after the machine has been turned off?
What caused a shock when the volunteer touched a fellow student?
Why did your teacher ground the generator before allowing the volunteer to step off the stool?
What is the role of the plastic stool?

Safety note: Make sure you ground the large sphere after each use by touching it with the ground wire or small sphere. Although the Van de Graaff generator produces a very low current, it may cause problems with people who have heart problems or a pacemaker. Warn students they may get small shocks which will scare them more than hurt them.

Part 1: Making Sparks

Touch the small sphere (connected to the ground wire) to the dome.
Turn the knob counter clockwise.
Turn the generator on.
Slowly turn the knob clockwise so the motor turns the belt.
Take the small sphere away and let a charge accumulate on the dome. Ask a student to turn off the lights to make it easier to see the sparks.
Move the small sphere around the sphere in different positions so that everyone can see the sparks.

Part 2: Sautéing Styrofoam

Ground the dome by touching the grounding rod to it.
Without removing the grounding rod, place Styrofoam peanuts (or confetti) on top of the large sphere.
Take the ground away, and the Styrofoam peanuts will fly off the generator.
This can be repeated by placing a metal pie panplate (or three!) on top of the generator and repeating the steps above.

Part 3: Hair-Raising Experience

Ask a student to step up onto the insulated stool.
Without removing the grounding rod, ask the volunteer to put one hand on the dome, the other hand by their side and make sure they understand not to move their hands until you tell them to.
Take the ground away, and their hair will start to stand up. Shaking their head will help too!
Hold the mirror so that the volunteer can see their new hair-do!
Ask the volunteer to move their hand from the ball to their side, and to keep it there. Immediately ground the Van de Graaffand then turn it off.
The volunteer can simply step off the stool or touch elbows with a classmate to get rid of their extra electrons (note: touching elbows will result in a shock!).
Place a piece of fake fur on the large sphere, the individual fur strands will stand.
Tape streamers to your volunteer, like an extra-long moustache!
Have someone hold onto the large sphere while blowing soap bubbles with a wand, the bubbles will become positively charged and will be attracted to anything that is grounded e.g. a person walking by.
A fly stick is a miniature, battery powered Van de Graaff generator. It charges mylar objects, which are then repelled by the stick (and by each other). You can make small objects hop up and down between the stick and your hand or levitate the more visible ones. For fun ideas, check out the Educational Innovations' teacher blog.

About the sticker

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Time-Travel T-Rex

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Science project, van de graaff generator experiments.

Lightning is the electronic discharge between particles in the air and clouds and the ground. Electricity is carried through current , or the flow of electrons, and lightning is caused by very large currents, which is why it can be so deadly when it strikes. Large currents that cause lightning also cause high voltages. Voltage is the “potential difference” between two places, meaning it describes the ability and likelihood of electric charge to flow from one place to another. If current is relatively low, voltage can be very high and still very safe. The Van de Graaff generator in this experiment operates at high voltages but low currents, similar to the static electricity you experience after rubbing your shoes on carpet and touching a doorknob on a dry day.

You may have seen a Van de Graaff generator in a science museum before. It is an electrostatic generator, and creates static electricity by building up very large voltages on its surface by moving a belt over a terminal and the electric charge accumulates on the surface of a hollow metal sphere. These spheres can hold high enough potential differences to produce a visible spark when objects are brought close. A small, table-top generator can get up to 100,000 V (volts)! One in a museum can get up to 5 megavolts—that’s 5,000,000 V! This is much higher than a typical battery, which is about 1.5 V. This apparatus was invited in 1929 by Robert Van de Graaff, an American scientist.

Explore concepts in current and voltage with a Van de Graaff generator.

What will happen if you touch the generator when it is on?

2 Van de Graaff generators
Rubber-soled shoes
Costume wig
Wear rubber-soled shoes! This will help insulate you from the ground.
Set up the Van de Graaff generator on a table top.
Touch the generator while it is off to discharge any static electricity currently on the surface.
Turn on the generator.
Touch it! What happens? How does it feel?
Keeping your hand on the generator that is on, bring your free hand closer to the metal fork. What happens?
Turn off the generator.
Place the costume wig over the generator. Turn it on and observe what happens.
Turn off the generator and remove the wig.
Take the metal object (like a fork) and rub it on an insulated object, like the carpet or clothing. Why do you have to do this?
Bring it close to the sphere and watch what happens.

Touching the generator while it’s on will cause your hair to stand up! Similarly, the hair on the wig will stand up when the generator is on. Bringing your free hand close to a metal object will discharge electricity from your body and you will hear an audible pop! Bringing a positively charged charged metallic object close to the negatively charged generator will produce a visible spark, like tiny lightning!

Rubber shoes help to insulate you from the ground, allowing charge to build up on your body rather than flow straight through you into the ground, the area with the lowest electric potential. A plastic stepping stool or other object made of insulated material would also work well. Carpet is also a decent insulator, which is why you can often scoot around the carpet with shoes on and shock your friends with the static electricity that you build up.

When the generator is on, it is negatively charged as the electrons amass on the sphere’s surface. When you touch the sphere, the electrons flow onto your body, which is neutrally charged. As the electrons flow over the surface, they reach the hairs on your arms and on your head. Like charges repel each other, and because the hairs are so light the charges repel enough to move the hair away from the rest of your body. This is the same reason the strands of the wig stand up.

The sound produced when static electricity is discharged is caused by the electrons jumping across the air barrier all at once! Lightning makes a sound as well, the electric discharge that happens in the air creates the audible boom we know as thunder. We see the lightning first before we hear the thunder because light travels faster than sounds.

Rubbing a metal object like a fork on the carpet or on fabric will cause many of the electrons to move onto whatever you are rubbing the object on. This will create a positively charged object. Bringing this near the negatively charged Van de Graaff generator can create a potential difference large enough to produce a visible spark. If you don’t get a spark, it is likely that your object is not positively charged enough.

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Note: All electrostatic demos work better on cold, dry days.

a. In this classic demonstration, the professor or a student volunteer stands on the insulated base and places his/her hand on the sphere of the generator. An assistant turns the generator on, and the demonstrator's hair stands on end. The demonstrator should have a key or other pointed object concealed on his person to hold up and spray off the excess charge when the demonstration is over. A similar effect can by demonstrated by placing a wig on the sphere, or by connecting the sphere to a paper plume. The electric flier shown below will spin by spraying off charge when connected to the sphere.

b. Two Van de Graaffs are provided, one of which charges its sphere positive, and the other negative. When both are turned on, they will spark to each other over 8 -12" distance. However, if a small point is placed on one sphere, aimed in any direction, even at the other sphere, no sparks will jump, because the point dissipates the charge into the air preventing the potential from building up.

c. When the pear-shaped metal sphere is charged by touching it to the Van de Graaff, a larger charge can be removed from the narrow end than from the fat end. The amount of charge is tested by the deflection of an electroscope. To produce a noticeable effect this demonstration must be done carefully.
	d. charge is on the outside of a conductor. Several demonstrations of these effects are described .
e. . A string connected between an electrostatic generator and an electroscope will not conduct charge, but a metal wire will.

f. . Smoke blown into a tube (from a cigarette) rapidly disappears when the electrodes on the ends of the tube are connected to the generator.
	g. " " A paper cup full of puffed wheat or small Styrofoam chips placed on top of the generator produces a spectacular effect. Bring your own puffed wheat.

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		of VDG machines
		on my web pages. Use your VDG as a power supply for the motor. If you ground one bottle of the motor, stand on a plastic insulator, touch the VDG sphere, and point at the other bottle of the motor, the motor will start to turn. It is powered by the charged wind coming from your fingertip. Initially hold your finger a couple of inches from the bottle until you get the demo working. I managed to slowly increase the distance to the motor, retuning the motor brushes each time for best operation, until I could point at a motor which was four feet away! By instead using a paperclip taped to the VDG sphere and bent so it pointed at the motor, I managed to run the bottle motor from 10 feet away! This was in dry weather, when the VDG was working very well.

Turn off VDG without pain

Sky Pie

DANCING BUBBLES

ELECTROSTATIC LEVITATION

MAGIC BLINKING WAND

FAUX - DOO

CRACKLE'S HAILSTORM

PLUS OR MINUS?

PAPERCLIP RAY

CONDUCTIVE "INSULATORS"

Procedure:

Drop several CO2 chips in the water so that a thin layer of fog forms.

Use tape and a wire to connect the tray to the sphere of your VDG. Charge the tray with respect to ground.

Move your hand slowly over the fog, keeping your hand a few inches above it. You'll see small mysterious furrows being carved in the fog by the invisible, narrow threads of "electric wind."

If your hands are extremely clean (no sharp microscopic defects), try wetting your fingers and brush them across fuzzy clothing to pick up some microscopic lint. Or instead try waving a torn bit of paper over the mist. The sharp paper fibers seem to generate these "threads" of charged air fairly well. If humidity is very low, then perhaps the paper should be made moist.

If you can locate a zerostat , a " Zerostat (tm) " record-cleaning gun (Discwasher Inc.), you can perform the following. Tape strips of tissue all over your VDG sphere. Turn it on so the strips stand out, then turn it off. The strips remain standing. Now "shoot" the sphere with the Zerostat gun. The strips will collapse!. This "gun" contains a Barium Titanate piezo crystal connected to a sharp needle in the gun's tip. Squeezing the trigger send a few microamps of charged wind out through the gun's tip. Ionized air is a conductor, so the presence of ionized air near the generator allows the charge on the sphere to leak away.

When explaining Van de Graaff machines it's probably a good idea to avoid the words "Static Electricity." A VDG machine is simply an electric power supply which has a characteristic of high voltage and low current output. This is in contrast to a dry cell battery. Dry cells are electric power supplies which give high current and low voltage output. While it's true that electric charge, charge imbalance, voltage, current, power, and energy exist, it is NOT true that there is a "stuff" called Static Electricity. Just because voltage and current may vary, that's no reason to invoke a new kind of "electricity" called "static." Van de Graaff machines and batteries do not differ as much as we might think. After all, if enough VDG machines are connected in parallel, their currents add up and they can light a normal incandescent bulb. And if enough dry cells are connected in series, their voltages add up and they can attract lint, raise your hair, charge your body, cause corona discharge, and make giant sparks. Electrostatics, or "Static Electricity," is a class of effects in the same way that "biology" or "weather" are classes of effects. Your hand is "biology", yet your hand is not made out of biology. Clouds are "weather", yet clouds are not composed of weather. And, while scuffing your shoes on the rug involves "static electricity," scuffing your shoes does not create any substance or energy called static electricity. If we always call it "electrostatics" instead of "static electricity", we won't be so confused about it's nature. If we say "surface charge", we won't be so surprised when it moves or flows ("Static" must be unmoving, right? Wrong, surface charges can and do flow.) Assume that the words "static electricity" breed confusion and ignorance, then avoid speaking them.

The Van de Graaf machine is a fun demo tool in museums, but it's also useful in science teaching. It can be used to demonstrate two important things: electric fields and electric forces. Everyone encounters magnets and magnetic fields, but few are aware that *electric* fields exist. These fields are usually hidden under the label "static electricity" and are ignored. This is unfortunate, since knowledge of electric fields leads to the understanding of sparks and lightning, voltage and circuits, and even the physical basis of chemistry and biology! In the functioning of the everyday world, e-fields are MUCH more important than magnetic fields, yet all the emphasis is placed on the latter. Students have difficulty understanding voltage because voltage *IS* electric fields, and if we don't understand electric fields, we will be befuddled by "voltage." The Van de Graaff machine is extremely useful because it produces electric fields which are strong enough to be measured, manipulated, felt directly, played with, and finally grasped at an intuitive level.

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7 Van De Graaff Generator Activities

A set of activities to show how the generator works and the principles behind it.

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Van De Graaff Activities

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Van De Graaff Generator

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How To : Experiment with a Van de Graaff generator

Try out this science experiment... watch this video tutorial to learn how to experiment with a Van de Graaff generator. This is purely educational, and demonstrates different techniques in using the Van de Graaff generator.

This is a collection of experiments using a Van de Graaff generator. The generator uses a belt and two rollers to build up a charge in the dome on top. The electrons will jump from the dome to reach a grounded object.

Since like charges repel one another, objects placed on top of the dome will become charged and then be repelled. This is the same machine sometimes used to make someone's hair stand up in classrooms or in science centers.

This is an easy science experiment you can do right at home.

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5 Fun Ways to Use a Van de Graaff Generator

The Van de Graaff generator is a common sight in the science lab. Van de Graaff generators operate using the following principles:

When different materials rub together, one loses electrons to the other. The material that gained electrons will have a negative charge and the material that lost electrons will have a positive charge. This is called the triboelectric effect.

Negative charges repel each other, but are attracted to positive charges. Similarly, positive charges repel each other, but are attracted to negative charges. When charges are repelled, it is called electrostatic repulsion.

When positive and negative charges are separated from one another, a potential difference is created. With a potential difference, electrostatic discharge can occur as electrons jump from the negatively charged object to the positively charged object.

Positive generators (like the Van de Graaff) create a positive charge by pulling electrons from the top of the machine toward the bottom. The positive charge surrounds the dome. Check out the fun demonstrations you can do with a Van de Graaff generator, all with this kit , perfect for every science lab!

Playing with Pith Balls

Materials: Van de Graaff generator and discharge wand, pith balls , tape

Plug the discharge wand into the base of the generator.

Tape the ends of the pith ball strings onto the dome of the Van de Graaff generator. You can put all the strings into a bundle or tape them around the dome at intervals.

Start the generator and observe how the pith balls behave. Bring the discharge wand close to the dome while the generator is still running. Turn off the generator and observe the behavior of the balls.

Discharge the generator and observe the behavior of the balls. Observe how the pith balls react to discharge.

Get the Spins with a Spiked Arm Wheel

Materials: Van de Graaff generator and discharge wand, spiked arm wheel

Place the pointed plug into the top of the dome and place the spiked arm wheel on top of the point.

Move the discharge wand as far away from the charging dome as possible. Turn the Van de Graaff on for about 10 seconds and observe what happens.

Does the wheel only rotate one way? Move the wheel in a circle clockwise and move the discharge arm so it is touching the collecting dome.

Turn the Van de Graaff on and then observe the wheel.

Now move the discharge arm away from the collecting dome so that charge begins to collect on the dome.

Observe the motion of the wheel. What happens?

This demonstrates how charge will collect on the outside of a charged surface and accumulate at a point. The points of the wheel will have a greater charge density and therefore more charge will emanate into the air from the point. Since charge has mass and that mass is leaving from the end of the wheel’s points, the wheel is propelled forward.

This fits with Newton's third law: for every action, there is an equal and opposite reaction. The charge leaves from the tips of the stars moving tangent and clockwise and the star therefore is pushed counterclockwise around in a circle.

Dancing Balls

Materials: Van de Graaff Generator; dancing ball accessories in a 6" long and 2" diameter glass tube; pith balls, vermiculite, or aluminum foil

Place the pith balls, vermiculite, or aluminum foil into the cylinder. Attach the cylinder to the top of the generator.

Switch on the generator and observe the contents in the cylinder for 30 seconds.

Avoiding the dome, bring a finger near to the metal top cap. Observe the change in behavior of the cylinder’s contents. What do you feel?

Move the finger further away then bring it back. How does the behavior of the contents of the cylinder change?

Because you are in contact with the ground (earth), you can supply electrons through your body, to the top cap of the tube. Why do the balls go down the tube, when your finger is near the top cap?

Light up the Night!

Materials: Van de Graaff generator and discharge wand, neon bulb pointer

This demonstration is best done in a darkened room.

Start the Van de Graaff generator.

Bring the neon bulb toward the dome of the generator.

Adjust the distance between the wand and dome, and observe how it affects both the interval between discharges and the brightness of their glow.

Turn off and discharge the generator.

How does it work? As you bring the wand near the generator, the electric field is strong enough to flow through the tube, exciting the neon atoms. As the atoms relax, they give off light, causing the wand to glow with neon’s characteristic red-orange color.

A Hair-Raising, Electrifying Time!

Materials: Van de Graaff generator, a wooden chair, a wooden stick (e.g., meter stick)

Set the Van de Graaff generator on a table and place the wooden chair a few feet from it.

Have someone sit or stand on the chair with their feet off the ground and the generator off (people with medium to long, fine hair make the best volunteers!).

Have the volunteer place their hand on the bulb of the Van de Graaff.

Turn on the generator. What happens?

After the demonstration has concluded, switch the generator off, then touch the volunteer with the wooden stick to draw off the remaining electric charge.

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Van De Graaff Generator

What is Van De Graaff Generator?

A Van de Graaff Generator is a device used for building up extremely high Potential Differences in the order of a few million (as high as 20 million volts). Currently, Van de Graaff Generator produces a Potential Difference of 5 Mega volts.

The Van de Graaff Generator was designed by Robert Jemison Van de Graaff in1929 A.D.

While standing on an insulated platform, if we touch the spherical part of this Generator, the charge of the sphere would pass along our body and would transmit to our hairs.

Since the same charge would produce on our hairs, and these charges would repel each other. This is what we could see in the picture below:

Van de Graaff Generators are delineated as the "constant current" electrostatic devices. When we put a load on a Van de Graaff Generator, the current remains constant., but the voltage alters with the load.

Introduction:

Van de Graaff Generator is one of the devices that has an insulating effect and helps insulate various objects by creating a very high Potential. There is the acceleration of particles that are observed. There is also the presence of atom smashers where the subatomic particles are exposed to high-speed acceleration and are then smashed into the target atoms. Due to this smash collision happening there is the production of other subatomic particles along with other high energy radiation being produced. In order to understand the use of the Van de Graaf Generator and its uses here is an article on Van De Graaff Generator - Introduction, Working, Principle, Construction and Uses via Vedantu that helps you get an idea about everything involved with the same.

Triboelectric Effect Seen in Van De Graaff Generator:

The triboelectric effect is a type of electrification in which certain materials tend to become charged electrically when they come into contact with one another and are then separated from each other. The polarity and strength of the charges that are being produced may differ in magnitude based on the materials that are used, surface roughness, temperature, strain, and other properties. To know more about the triboelectric effect students can also access the Vedantu NCERT Solutions for Class 12 Physics which provides a detailed view on the same.

On this page, we will learn about the following:

Working, principle, and construction of Van De Graaff Generator

Uses of Van De Graaff Generator

Van de Graaff Generators are “Constant Current ” Electrostatic devices that work mainly on the two principles:

Corona discharge.

Accumulation of charge on the outer sphere.

Construction

(Image will be Uploaded Soon)

Van De Graaff Generator Consists of the Following:

An outer terminal - An aluminum or steel sphere

Upper brush - A piece of fine metal wire

Upper pulley (P1) - A piece of nylon

A long narrow conveyor belt of insulating material like Silk, rayon or rubber wound around the pulleys P1 and P2

Lower brush

Lower pulley (P2) - A piece of nylon covered with silicon tape.

B1 - Sharply pointed spray comb

B2 - Sharply pointed collecting comb

When the spray comb is given a positive Potential (= 10 4 volts) w.r.t. the earth via the high tension source H.T. Due to corona discharge action of sharp points, a positively charged electric wind is set up, which sprays a positive charge on the belt as soon the motor is turned on, the lower pulley (P2) begins turning the positively charged belt upwards, and the lower pulley (P1) establishes a negative charge. Since the pulley P2 is capturing electrons from the belt which is passing over this pulley P2.

Here, we can see that the charge on the pulley P2 is more concentrated than the belt because a strong electric field is generated at the lower pulley.

As the belt reaches the sphere, a negative charge builds upon the collecting comb B2 and a positive charge on the farther side of the comb B2.

This positive charge shifts to the outer surface of S. The discharging action of sharp points of the comb B2, a negatively charged electric wind is set up. Which in turn would neutralize the coated positive charge on the belt, and the belt would turn down again.

The belt will collect the positive charge from comb B1, and then would be collected by the comb B2.

This process continues, the charge accumulates on the sphere S and the excess charge shows up on the outer surface of the sphere.

Capacitance of electrical sphere

C = \[ 4 \times π \times 𝔪o \times R \] (R =radius of the shell)

C = \[ \frac {Q}{V} = \frac {V}{4 \times π \times 𝔪o \times R } \]

Where V is the Potential Difference

C = Capacitance

Q= The charge in the spherical shell

𝔪o =Permittivity of free space

Hence, the Potential Difference V increases with an increase in charge Q.

As soon as the Potential of the shell exceeds the breakdown field value of air (\[3 \times 10^{6}\] Volt /meter), the air around S gets ionized, and leakage occurs.

This leakage is minimized by housing the shell inside the steel chamber filled with nitrogen and methane at high-pressures.

Uses of Van de Graaff Generator

Particle Accelerators

These accelerators are also known as Particle Smashers. The high energy supply by the Generator accelerates the subatomic particles in an evacuation tube, and these particles crash into atoms.

The ability of a Generator to create these high-energy collisions is the cornerstone of Particles and used to accelerate ions, protons, and electrons needed for various experiments of Nuclear physics.

These Generators are used as accelerators to generate X-Ray beams for nuclear research and nuclear medicine.

Science Education

In physics education to teach Electrostatics.

Sterilizing Food

Accelerates electrons to sterilize food and process materials

There are two kinds of Van de Graaff Generators: The one employs high-voltage power supply for charging and one utilizes belts and rollers for charging.

Van de Graaff Generator, as we set about the output terminal (sphere) with a grounded object, the voltage will decrease, but the current will remain the same.

The charges are produced due to friction by two insulating bodies rubbing against each other, and they can’t move on their own (at rest) which means they (charges) are static by nature are called Static charges.

FAQs on Van De Graaff Generator

1. How can you Prevent Corona Discharge?

Corona discharge depends upon various factors:

Shape: A smooth surface (electric field uniformly spreads) would have less corona than the stranded surface (as electric field distributes over the surface at different locations).

Size: Conductors having a large diameter have fewer chances of corona discharge.

Line Voltage: Lesser the line voltage, less will be the corona discharge.

2. How can the whole Charge of a Conductor be Transferred to another Isolated Conductor?

This can be done by placing a hollow insulated conductor inside the charged conductor and connecting the two conductors by a wire, the whole charge will shift to the isolated conductor.

3. A Spherical Shell of Radius k with Charge D is Spread out to Radius h. Find the Work done by the Electrical Force in this Procedure.

Work done = Initial Stored energy - final stored energy

Since the formula is given by W=\[ \frac {1}{2} \times D^{2} \frac {𝔪}{r}\]

=\[\frac {1}{2} \times D^{2} \frac {4}{π} \times {𝔪} \times {k}- \frac {1}{2} \times D^{2} \frac {4}{𝔪} \times {π} \times {h}\]

Therefore, Work done = \[ D ^{2} \frac {8}{π} \times {𝔪}\]

4. Two Insulated Spheres of Radii 40 cm and 56 cm Holding a Similar Charge are Wired by a Conductor and then they are Set Apart. Which of the Two Spheres will Carry More Charge?

Bigger sphere will carry more charge as its capacity is larger (D = M x G). The Potential Difference G turns the same on getting them attached with a wire.

5. What are the components of the Van De Graaff Generator?

The components of the Van De Graaff Generator can be provided as follows:

1. Hollow metal sphere supported by insulating supports through its sides

2. Upper electrode

3. Upper gaseous roller (for example it can be an acrylic glass)

4. Side of the belt with the presence of positive charges

5. The opposite side of the belt with negative charges being present

6. Lower metal roller

7. The lower ground electrode

8. An aspherical device with negative charges present

9. The spark that is produced due to the presence of different Potentials

6. What is the use of learning about the Van De Graaff Generator - Introduction, Working, Principle, Construction and Uses via Vedantu?

By learning about the Van De Graaff Generator - Introduction, Working, Principle, Construction, and Uses via Vedantu students get to learn regarding the following:

1. Students can learn how to use the Van De Graaff Generator for creating a Potential that ranges around a few million volts

2. How the protons, deuterons, etc can be accelerated and hence bring about artificial transmutation

3. It will help to learn more about collision experiments that are present in Physics

4. How the beams involved can be used to treat cancer.

7. Where is the Van De Graaff Generator used?

In recent times the Van De Graaff Generator is largely used to demonstrate various aspects and concepts involved in the electrostatic behavior of particles in academic sessions. However, in the earlier times, it was mainly one of the sources that were used to accelerate various subatomic particles. Now due to the advancements in science, it has become possible to use much better instruments than Van De Graaff Generator. Even if the use of the Van De Graaff Generator is very restricted to only demonstration purposes, it once used to have a good history as a part of nuclear physics.

8. What are the limitations of the Van De Graaff Generator?

There are certain limitations with its usage and these limitations can be provided as follows:

1. It has a series combination that allows only one route for the motion of the charges that are involved, hence making it impossible for the scattering of particles.

2. It can only be used to accelerate the charged particles and not the uncharged particles. Hence it has only a limited range of applications.

Due to these two limitations, it is not feasible to use the Van De Graaff Generator for measurement purposes. The charge being involved is also quite dangerous and hence is only allowed for demonstration purposes.

9. What are the precautions and safety measures needed to be taken while accessing the Van De Graaff Generator?

Van De Graaff Generator is an instrument that dissipates a high amount of charge hence there needs to be some precautions and safety measures that needs to be followed:

1. Those people who have cardiac pacemakers attached should not be close to the Van De Graaff Generator or even come in contact with it

2. While the Van De Graaff Generator is being charged make sure that you stay at least three feet away.

3. Always make sure that you discharge the collector dome between two experiments when you are done with the demonstration. You can use the discharge wand for this purpose.

4. The voltage is so high that it can make its way to your body through the discharge wand and hence make sure you hold it only by the handle and do not touch anywhere else.

5. Do not run the Van De Graaff Generator for a longer period of time continuously

6. Make sure you have kept the entire device dry and clean

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Van de Graaff Generator facts for kids

A Van de Graaff generator is an electrostatic machine . It uses a moving, nonmetallic belt to accumulate very high voltages on a hollow metal globe . Voltage differences achieved in modern Van de Graaff generators can reach 5 megavolts. Applications for these high voltage generators include driving X-ray tubes, accelerating electrons to sterilize food and process materials, and accelerating protons for nuclear physics experiments. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance. It is named after the American physicist Robert Jemison Van de Graaff , who built the first generators of this style in 1929 .

Images for kids

Spark by the largest air-insulated Van de Graaff generator in the world at The Museum of Science in Boston , Massachusetts

This Van de Graaff generator of the first Hungarian linear particle accelerator achieved 700 kV during 1951 and 1000 kV during 1952.

A Van de Graaff particle accelerator in a pressurized tank at Pierre and Marie Curie University, Paris

This page was last modified on 16 October 2023, at 16:53. Suggest an edit .

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COMMENTS

Experiments with a Van de Graaff generator
Procedure. Show the Van de Graaff generator, and describe it as a machine transporting charges to its large sphere. Bring up the light, conducting polystyrene sphere, suspended on a long insulating nylon thread from an insulating rod. Let the small sphere touch the large sphere, sharing some of the charge and the repulsion between like charges ...
Van de Graaff Experiments
When the Van de Graaff generator starts charging, it transfers the charge to the person who is touching it. Since the person's hair follicles are getting charged to the same potential, they try to repel each other. This is why the hair actually stands up. It would not make a difference if the polarity of the Van de Graaff generator were reversed.
Van de Graaff generator
Sparks from the Van de Graaff are typically a few centimetres long, giving a voltage between 50,000 and 150,000 V. Their propensity to generate sparks is the fundamental limitation of Van de Graaff accelerators, or indeed any accelerator design based on a large, static voltage. Those used for research managed to get up to over 20 MV by clever ...
Van de Graaff generator
A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials.It produces very high voltage direct current (DC) electricity at low current levels. It was invented by American physicist Robert J. Van de Graaff in 1929. [1]
Van de Graaff Experiments
search. E.1.2 Experiments with Van de Graaff Generators. Note: All electrostatic demos work better on cold, dry days. a. Charge flows to the points and sprays off. In this classic demonstration, the professor or a student volunteer stands on the insulated base and places his/her hand on the sphere of the generator.
Van De Graaff Generator Wonders
Van de Graaff experiments are all based on the fact that like charges repel. A Van de Graaff generator pulls electrons from the Earth, moves them along a belt and stores them on the large sphere. These electrons repel each other and try to get as far away from each other as possible, spreading out on the surface of the sphere.
Van de Graaff Generator Experiments
The Van de Graaff generator in this experiment operates at high voltages but low currents, similar to the static electricity you experience after rubbing your shoes on carpet and touching a doorknob on a dry day. You may have seen a Van de Graaff generator in a science museum before. It is an electrostatic generator, and creates static ...
110. Van de Graaff Experiments
110. Van de Graaff Experiments. Note: All electrostatic demos work better on cold, dry days. a. Charge flows to the points and sprays off. In this classic demonstration, the professor or a student volunteer stands on the insulated base and places his/her hand on the sphere of the generator. An assistant turns the generator on, and the ...
Van de Graaff generator: Hints, Demonstrations, and Activities
When explaining Van de Graaff machines it's probably a good idea to avoid the words "Static Electricity." A VDG machine is simply an electric power supply which has a characteristic of high voltage and low current output. This is in contrast to a dry cell battery. Dry cells are electric power supplies which give high current and low voltage output.
7 Van De Graaff Generator Activities
7 Van De Graaff Generator Activities Environmental Science, Physical Science, Physics, Life Science, Earth Science, A set of activities to show how the generator works and the principles behind it. Full Lesson Plan >
Van de Graaff generator
A Van de Graaff generator can produce extremely high potential differences (voltages). A small school version can pump a huge charge onto the top dome so that the potential difference between the dome and the earth can be 200 000 volts yet the total charge is so tiny that you only receive a small shock when you touch it. This makes possible dramatic demonstration experiments which convey ...
PDF Experiment 5: Van de Graaff
• The Van de Graaff generator is notoriously unreliable and can go from creating fabulous sparks to nothing in the matter of minutes, or vice-versa • Cleaning the dome with detergent can help to remove grease, and blowing a hairdryer to warm the dome and surrounding air can improve performance dramatically Experiment 5: Van de Graaff
Van de Graaff generators in the classroom: Theory, operation, and
Van de Graaff generators in the classroom: Theory, operation, and safety. 20 April 1998. Theory. The generator uses a Teflon pulley at the lower end of the machine, attached to an electric motor. A rubber belt passes over the pulley. ... Always discharge the collector dome between experiments and when you are finished. Use the discharge wand ...
PDF Instructions Applications for Van De Graff Generator
Introduction: The Van de Graaff generator deposits a very large amount of positive electrical charge on the metal dome (oblate, globe). This massive volume of positive electrical charge produces a spectacular display of lightning and other phenomena. When two insulators are rubbed together, one loses electrons to the other and becomes ...
Experiment with a Van de Graaff generator
Try out this science experiment... watch this video tutorial to learn how to experiment with a Van de Graaff generator. This is purely educational, and demonstrates different techniques in using the Van de Graaff generator. This is a collection of experiments using a Van de Graaff generator. The generator uses a belt and two rollers to build up a charge in the dome on top. The electrons will ...
PDF 5 SAFE EXPERIMENTS USING A VAN DE GRAAFF!
Using a Van de Graaff you can show random motion of metallic balls continuously affected by repulsion and loss of charge within a transparent vessel. To carry out this experiment attach a transparent tube (filled with aluminum foil balls) to the top of the dome, switch on the Van de Graaff and watch the balls randomly move around the cylinder.
Cool Experiments: Van de Graaff Generator
The first video of a new series called "Cool Experiments" from Beauty of Science. This video is about a few interesting experiments done with a Van de Graaff...
PDF Washington University in St. Louis Electrostatics Lab Introductory
The big piece of equipment in this week's experiment is a Van de Graaff generator powered by a hand crank. A Van de Graaff generator uses some clever tricks in order to charge a metal dome to a very high potential. The University of Virginia has an excellent virtual demonstration of the inner workings of the Van de Graaff generator.
5 Fun Ways to Use a Van de Graaff Generator
The Van de Graaff generator is a common sight in the science lab. Van de Graaff generators operate using the following principles: When different materials rub together, one loses electrons to the other. The material that gained electrons will have a negative charge and the material that lost electrons will have a positive charge. This is called the triboelectric effect. Negative charges repel ...
Van De Graaff Generator
1. Students can learn how to use the Van De Graaff Generator for creating a Potential that ranges around a few million volts. 2. How the protons, deuterons, etc can be accelerated and hence bring about artificial transmutation. 3. It will help to learn more about collision experiments that are present in Physics.
Van de Graaff Generator facts for kids
A Van de Graaff generator is an electrostatic machine. It uses a moving, nonmetallic belt to accumulate very high voltages on a hollow metal globe. Voltage differences achieved in modern Van de Graaff generators can reach 5 megavolts. Applications for these high voltage generators include driving X-ray tubes, accelerating electrons to sterilize ...
Painful Experiments with Van De Graaff Generator
A Van de Graaff Machine can be specially helpful to learn about charges and high voltage, as well as very painful if you don't handle it right!It would be pr...
A hair-raising experience with a Van de Graaff generator
From Vancouver's Science World: "A Van de Graaff generator pulls electrons from the Earth, moves them along a belt and stores them on the large sphere. These electrons repel each other and try to get as far away from each other as possible, spreading out on the surface of the sphere. The Earth has lots of room for electrons to spread out ...