Static “Hair” Wand

Introduction

This classic physics demonstration uses a high-voltage Van de Graaff generator to charge up a “volunteer” with long, straight hair. Unfortunately, individuals with static-friendly hair may not be in every classroom. Luckily, anyone can become a hair-charged volunteer when they hold a wand with thin fiber strands.

Concepts

• Van de Graaff generator
• Static electricity
• Repulsive forces

Materials

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 they remove their hand 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 wood meterstick). Then touch the charged individual with the wood rod to slowly discharge him. The “hair” fibers 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.

Procedure

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 that is far 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 (see Figure 1). Again, make sure 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 (see Figure 1).
   {13931_Procedure_Figure_1}
5. Have the student touch the top of the Van de Graaff generator dome with the palm of their free hand (see Figure 1).
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.
7. Have the volunteer hold the hair wand at shoulder level (see Figure 1).
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 1-m wood dowel rod.
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. Are the strands shooting upward and spread apart? (Twirling the wand helps to untangle and loosen the fibers.)
11. What does the volunteer experience? Is the volunteer’s hair standing up? How do his clothes feel? Is there a tingling sensation?
12. When finished with the observations, turn the Van de Graaff generator off using the wood dowel rod to flip the ON/OFF Switch. Warning: Do not allow the volunteer to remove his hand from the dome until he is discharged.
13. 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.
14. Once discharged, the volunteer can remove his hand from the dome and step off the insulated platform.
15. Repeat with other “volunteers” as time allows.

Teacher Tips

• 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 more conducive to electrostatic demonstrations.
• 350,000- to 400,000-volt Van de Graaff generators, such as Flinn Catalog No. AP6476, work the best for this demonstration.
• Insulated plastic step-stools, thick blocks of wood (4" x 6"), and plastic milk crates work well as insulating platforms.
• Refer to the Flinn Scientific Publication No. 10552, Van de Graaff Generator Safety, for additional safety information.

Discussion

A Van de Graaff generator builds up positive electric charge on its dome by separating negative static electric charge from positive static electric charge using a quickly moving belt. The positive charge collects on the large metal dome of the generator. When the charge build-up is large enough, a lightning-like spark can shoot from the dome to a grounded discharge rod.

A hair-raising demonstration using a Van de Graaff generator is a classic way to show the repulsive nature of like electric charges. Like electric charges repel, whereas opposite electric charges attract. When an individual is charged by a Van de Graaff generator, he attains the same positive charge polarity as the dome. Therefore, a positive charge accumulates over the entire surface of the individual, including the fiber strands of the wand. Each fiber strand becomes positively charged so all the fibers repel each other. The repulsive forces between the fibers are strong enough to overcome the force of gravity pulling the fibers down. So, in an attempt to spread as far away from other fibers as possible to minimize the repulsive forces, the fibers strands stand up and spread apart.