# The Van de Graaff Generator

## Demonstration Kit

### Introduction

The Van de Graaff Generator is a fun and exciting tool to teach students about static electricity and repulsive forces. Try these hair-raising demonstrations for an unforgettable learning experience!

### Concepts

• Conduction
• Electric forces
• Van de Graaff generator
• Electric charge
• Electrostatics

### Background

The first Van de Graaff generator was built in 1929 by Dr. Robert J. Van de Graaff (1901–1967). This high voltage electrostatic generator was once used to accelerate particles for nuclear physics experiments. The Van de Graaff generator functions using the basic principles of electrostatics.

The term electrostatics (or static electricity) means electricity at rest, and involves the behavior of electric charges and the nature of electric force. The electric charge on an object is determined by the number of protons and electrons in its atoms. Protons have a positive charge, and electrons have a negative charge. Most objects in our everyday lives are neutral, which means their atoms have equal numbers of protons and electrons. An object becomes charged by either losing or gaining electrons. This most often occurs through conduction, the charging of an object by direct contact. If an object gains electrons from another object, its net charge will be negative, and if it loses electrons its net charge will be positive. Objects gain or lose electrons depending on their atomic or molecular makeup.

Electric force is the attraction or repulsion (push or pull) that occurs between charged objects. Objects that have opposite charges attract while like charges repel. Attraction will also occur between a charged object and a neutral object. This is because charge likes to balance out between objects, and any difference in charge will result in a force between the two objects. An electric force will not exist between two or more neutral objects because charge is already balanced between them.

The Van de Graaff generator is known as an electrostatic generator because it gains a charge. The generator consists of a motor, rubber belt, circular dome, upper roller, lower roller, upper wire brush, and lower wire brush (see Figure 1). The motor is used to spin the lower roller, which in turn rotates the rubber belt. As the rubber belt moves across the lower roller, frictional contact between the two different materials causes electrons to be transferred from the roller to the belt or vice versa. The Van de Graaff generator can obtain either a positive or negative charge depending on the composition of the rollers. If the dome gains a negative charge, this means that electrons are carried up the belt and deposited on the dome (see Figure 1). If the dome attains a positive charge, electrons are being removed from the top of the dome and carried down the belt. Regardless whether the net charge is positive or negative, like charges will repel and move as far away from each other as possible, spreading to the outside of the dome. The dome of a Van de Graaff generator is often circular because charge tends to leak off objects with sharp edges. Therefore a circular or round dome will hold charge better than any other shape. For further information on how a Van de Graaff generator works, see Publication No. 10552, Van de Graaff Generator Safety, available for free on www.flinnsci.com. It also explains in detail how a Van de Graaff generator’s dome gains a positive charge.

{12734_Background_Figure_1}

### Materials

(for each demonstration)
Discharge electrode
Foam peanuts, 15*
Insulated platform, wood or plastic, at least 12" x 12" x 6" H
Meter stick, wood (no metal), or 1-m wood dowel rod, ½" dia
Neon wand*
Plastic cup, clear, 10 oz*
Safety glasses
Safety shield
Static “Hair” wand*
Tart pans, aluminum, 4¼", 5*
Van de Graaff generator, high-voltage
*Materials included in kit.

### Safety Precautions

Van de Graaff generators produce a very small current (microamps) and therefore an accidental shock from a Van de Graaff generator may cause pain and be startling, but the shock should not cause serious harm to most individuals, even at a high voltage. When working with a Van de Graaff generator it is important to have a metal discharge electrode connected to the Van de Graaff generator terminal. This acts as a ground and allows an operator to discharge the generator safely before getting near it. However, individuals who are charged for “hair-raising” demonstrations need to be discharged in a slow, controlled manner before removing their hands from the Van de Graaff generator dome. Do NOT use a metal discharge electrode to discharge a charged individual. Discharge a charged person using the following method: Turn off the Van de Graaff generator with a long wood rod or stick (such as a wooden meter stick). Then touch the charged individual with the wood rod to slowly discharge him or her. Hair strands will fall when the individual is completely discharged. Once discharged, the volunteer can remove his hand from the Van de Graaff generator dome. Do NOT touch the charged volunteer with anything other than an insulated wooden rod, or a painful shock to both the volunteer and the operator may result. Do not use Van de Graaff generators near flammable gases or vapors. Do not touch a Van de Graaff generator with wet hands or damp clothing. Use a Van de Graaff generator with an ON/OFF switch to prevent accidental shocks when performing “hair-raising” demonstrations.

### Disposal

All materials in this kit can be saved for future demonstrations.

### Procedure

Caution: Wear safety glasses and use a safety shield when doing the neon wand demonstration. The wooden meter stick used for all the demonstrations must be free of metal!

Demonstration 1. Let the Sparks Fly!

1. Obtain a Van de Graaff generator, discharge electrode and a wooden meter stick.
2. Place the Van de Graaff generator on a table away from grounded metal objects such as water faucets, door knobs, or metal tables.
3. Attach the discharge electrode to the proper location on the base of the Van de Graaff generator.
4. Turn off the lights in the classroom.
5. Hold the discharge electrode in one hand and the wooden meter stick in the other hand. Stand approximately one meter away from the Van de Graaff generator and turn it on by flipping the ON/OFF switch using the wooden meter stick.
6. Allow the Van de Graaff generator to run for 30 seconds or more to gain a static charge.
7. Bring the discharge electrode near the sphere of the Van de Graaff generator. Allow the students to watch as a spark flies between the sphere of the generator and the discharge electrode (see Figure 2).
{12734_Procedure_Figure_2}
8. Repeat steps 6 and 7 until all students observe the spark.
9. When finished with the observations, turn the Van de Graaff generator off by using the wooden meter stick to flip the ON/OFF switch. This will prevent static shock from the generator.
10. After the Van de Graaff generator is off, discharge its dome using the discharge electrode or wooden meter stick.
Demonstration 2. What a Blast!
1. Obtain a Van de Graaff generator, discharge electrode, wooden meter stick, plastic cup, foam peanuts and transparent tape.
2. Place the Van de Graaff generator on a table away from grounded metal objects, such as water faucets, door knobs or metal tables.
3. Attach the discharge electrode to the proper location on the base of the Van de Graaff generator.
4. Using transparent tape, secure a plastic cup to the top of the Van de Graaff generator.
5. Fill the plastic cup with foam peanuts (see Figure 3).
{12734_Procedure_Figure_3}
6. Hold the discharge electrode in one hand and the wooden meter stick in the other hand. Stand approximately one meter away from the Van de Graaff generator and turn it on by flipping the ON/OFF switch using the wooden meter stick.
7. Allow the students to observe as the foam peanuts “fly” out of the cup.
8. When finished with the observations, turn the Van de Graaff generator off by using the wooden meter stick to flip the ON/OFF switch. This will prevent static shock from the generator.
9. After the Van de Graaff generator is off, discharge its dome using the discharge electrode or wooden meter stick.
10. Remove the plastic cup and tape from the top of the Van de Graaff generator.

Demonstration 3. Flying Saucers!

1. Obtain a Van de Graaff generator, discharge electrode, wooden meter stick and five aluminum foil tart pans.
2. Place the Van de Graaff generator on a table that is far from grounded metal objects such as water faucets, door knobs, or metal tables.
3. Attach the discharge electrode to the proper location on the base of the Van de Graaff generator.
4. Stack the five tart pans on top of each other and place them upside down on the dome of the Van de Graaf generator (see Figure 4).
{12734_Procedure_Figure_4}
5. Hold the discharge electrode in one hand, and the wooden meter stick in the other hand. Stand approximately one meter away from the Van de Graaff generator and turn it on by flipping the ON/OFF switch using the wooden meter stick.
6. Allow the students to observe as the tart pans “fly” away from the dome one by one.
7. When finished with the observations, turn the Van de Graaff generator off by using the wooden meter stick to flip the ON/OFF switch. This will prevent static shock from the generator.
8. After the Van de Graaff generator is off, discharge its dome using the discharge electrode or wooden meter stick.
Demonstration 4. A Hair-Raising Experience!

Caution: The student volunteer must stand on an insulated platform during this demonstration. Example of insulating materials that may be used are plastic or wooden step-stools, wooden pallets and plastic milk crates.
1. Obtain a Van de Graaff generator, discharge electrode, wooden meter stick, wood or plastic insulated platform and the static “hair” wand.
2. Place the Van de Graaff generator on a table away from grounded metal objects such as water faucets, door knobs or metal tables.
3. Place the insulated platform next to the Van de Graaff generator on the floor. Make sure that the platform is not near any grounded metal objects.
4. Ask a student volunteer to stand on the insulated platform and hold the static “hair” wand in one hand. Caution: The student should remove any metal jewelry he or she may be wearing during this demonstration, including earrings.
5. Have the student touch the top of the Van de Graaff generator dome with the palm of his or her free hand (see Figure 5).
6. Warn the student volunteer that he is now insulated from the ground and that he will be charged with static electricity by the Van de Graaff generator. He cannot remove his hand from the Van de Graaff generator dome or touch any objects not insulated from the ground during this demonstration until he has been completely discharged and is instructed to do so by the Van de Graaff generator operator. If he lets go of the Van de Graaff generator during the demonstration, he will receive a static electric shock that could be painful. Note: Inform the student that he or she may experience a tingling sensation during this demonstration.
7. Have the volunteer hold the hair wand at shoulder level (see Figure 5).
{12734_Procedure_Figure_5}
8. Stand approximately one meter away from the Van de Graaff generator and the volunteer. Turn on the Van de Graaff generator by flipping the ON/OFF switch using the wooden meter stick.
9. Allow the Van de Graaff generator belt to build up to full speed.
10. Observe the fibers on the wand held in the volunteer’s hand. Observe the volunteer’s hair.
11. When finished with the observations, turn the Van de Graaff generator off by using the wooden meter stick to flip the ON/OFF switch. This will prevent static shock from the generator. Warning: Do not allow the volunteer to remove his hand from the dome until he is discharged.
12. After the Van de Graaff generator is off, discharge the volunteer by touching the Van de Graaff generator’s dome with the wooden meter stick. The wand’s fibers will slowly fall as the static electricity slowly “bleeds” off the volunteer. Once the fibers have fallen completely, continue to touch the dome with the meter stick for another 15 seconds to make sure the volunteer is completely discharged.
13. Once discharged, the volunteer can remove his or her hand from the dome and step off the insulated platform.
14. Repeat with other volunteers as time allows.
Demonstration 5. The Neon Wand!

Caution: The neon wand is a tube under low pressure and is subject to implosion if broken. Place a safety shield in front of the Van de Graaff generator, and wear safety glasses when performing this demonstration.
1. Obtain a Van de Graaff generator, discharge electrode, wooden meter stick, safety shield, safety glasses and a neon wand.
2. Place the Van de Graaff generator on a table away from grounded metal objects such as water faucets, door knobs or metal tables.
3. Attach the discharge electrode to the proper location on the base of the Van de Graaff generator.
4. Place the safety shield about 1½ to 2 meters away from the Van de Graaff generator (see Figure 6). Put on safety glasses.
{12734_Procedure_Figure_6}
5. Turn off the lights in the classroom.
6. Hold the discharge electrode in one hand and the wooden meter stick in the other hand. Stand approximately one meter away from the Van de Graaff generator and turn it on by flipping the ON/OFF switch using the wooden meter stick.
7. Set the wooden meter stick down and pick up the neon wand. Hold the neon wand between the safety shield and the Van de Graaff generator (see Figure 6). Slowly move the neon wand toward the Van de Graaff generator (keeping the wand between the safety shield and the Van de Graaff generator) until an orange glow is observed.
8. Allow students to observe the orange glow of the neon wand.
9. When all students have observed the orange glow, put the neon wand down and turn the Van de Graaff generator off by using the wooden meter stick to flip the ON/OFF switch. This will prevent static shock from the generator.
10. After the Van de Graaff generator is off, discharge its dome using the discharge electrode or wooden meter stick.

### Student Worksheet PDF

12734_Student1.pdf

### Teacher Tips

• If the wooden meter stick has metal tips, be sure to remove them before the demonstration.
• Static electricity experiments and demonstrations always work best on a dry day. Lower humidity days are better than high humidity days. Air-conditioned air or heated winter air tends to be drier and thus more conducive to electrostatic demonstrations.
• The neon wand will also glow orange for a brief second when rubbed with animal fur.
• High voltage Van de Graaff generators 350,000- to 400,000-volt, such as Flinn Catalog No. AP6476, work the best for these demonstrations.
• Sturdy plastic or wooden step-stools and plastic milk crates work well as insulating platforms.
• Refer to the Flinn Scientific Publication No. 10552, for additional safety information.

### Science & Engineering Practices

Developing and using models
Analyzing and interpreting data
Engaging in argument from evidence

### Disciplinary Core Ideas

MS-PS2.B: Types of Interactions
HS-PS1.A: Structure and Properties of Matter
HS-PS3.C: Relationship between Energy and Forces

### Crosscutting Concepts

Cause and effect
Systems and system models
Energy and matter

### Performance Expectations

HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
HS-PS2-5: Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.
HS-PS3-5: Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.
MS-PS2-3: Ask questions about data to determine the factors that affect the strength of electric and magnetic forces

Demonstration 1. Let the Sparks Fly!

Observations

Sparks fly between the dome of the Van de Graaff generator and the discharge electrode.

Explanation

Electric charge tends to balance out between objects. When the Van de Graaff generator is turned on, it begins to accumulate a charge, while the discharge electrode remains neutral. When the discharge electrode is brought near the Van de Graaf, the generator will discharge in order to balance the electric charge between the two objects.

Demonstration 2. What a Blast!

Observations

The foam peanuts fly out of the cup.

Explanation

Like charges repel, whereas opposite charges attract. The foam peanuts are in contact with the Van de Graaff generator and therefore attain the same charge polarity as the dome. Because all of the foam peanuts are the same charge, they repel each other.

Demonstration 3. Flying Saucers

Observations

The aluminum tart pans fly off the Van de Graaff generator one at a time.

Explanation

Like charges repel, whereas opposite charges attract. The tart pans are in contact with the Van de Graaff generator and therefore attain the same charge polarity as the dome. Because all of the tart pans are the same charge, they repel each other.

Demonstration 4. A Hair-Raising Experience!

Observations

The fiber strands on the static hair wand stand up. The volunteer’s hair may also stand up.

Explanation

Like charges repel, whereas opposite charges attract. When an individual is charged by a Van de Graaff generator, he or she attains the same charge polarity as the dome. This charge accumulates over the entire surface of the individual, including the fiber strands of the wand the individual is holding. With each fiber strand obtaining the same charge, the fiber strands repel each other. The repulsive forces between the fibers are strong enough to overcome the force of gravity. So, in an attempt to spread as far away from other fibers as possible to minimize the repulsive forces, the fiber strands stand up and spread apart. The same phenomenon may occur with the volunteer’s hair, especially if it has been recently washed and contains little or no hair care products.

Demonstration 5. The Neon Wand!

Observations

The neon wand glows an orange color when brought near the Van de Graaff generator.

Explanation

The Van de Graaff generator is providing a voltage (electrical energy) that excites the gas inside the neon tube. As the gas atoms absorb energy, electrons are “promoted” or “jump” to higher energy levels according to the Bohr model or quantum theory of the atom. When these electrons fall back to their ground state, they release energy in the form of light.

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