Electric Field: Electric Fields & Potential
Hair on End
PIRA Class: 5B10.10

Purpose
To illustrate the electric field about a charged object.

Description
Standing on an insulated stand with one hand on a Van de Graff generator, long hair can be observed to fly radially outward.
(See Demo: 5A50.30 Van de Graff Generators for demo preparation and Van de Graff operation)

Beforehand:
-On the day before / week prior to your classroom demonstration, make sure Van de Graff control box is plugged in and heater is turned on. This will reduce moisture within the Van de Graff.
-Check the base's desiccant stores. If desiccant is pink instead of blue, it needs to be replaced (or dried out in a 400 oven for 12 hours.)
- If during trial run no discharge is produced (and all connections, etc. are in order), securely attach a grounding lead from dome to base (with duct tape) and run belt motor for ~30 minutes. (No HV!) This will help remove excess humidity from inside dome.

In Class:
1. Locate Van de Graff in classroom 5 feet away from any student/ student desk/ classroom electronics/ etc. (Van de Graff has been seen to fry a computer's muse board. That's right, Fried Mice in class!)
2. Make sure grounding rod and control box connections with Van de Graff base are secure.
3. Choose a pace-maker free student with oil-free, relatively well groomed, med./ long hair. Have student remove any metal objects/ jewelry, especially from the side of their body that will be closest to Van de graff. (Small earrings are ok; Van de Graff has been known to discharge to students' metal shoe buckles.)
4. Have student stand on insulating stand and place one or both hands firmly (and flatly) of Van de Graff dome. (Inform student that if they remove their hand from the dome at any time durin the demonstration, they should not put it back on the dome.)
5. While holding grounding rod pole in one hand, flip on belt motor at control box with the other.
6. Flip on HV (high voltage) at control box. Observe hair to stand on end, illustrating the electric field about the student's head.
7. To turn off Van de Graff, turn off High Voltage first and then the belt motor. As student's hair falls back down, have student remove hand. Once hair is fairly "back in Place", student may step off of insulating stand. By rubbing shoulders with another, most excess charge will be removed.
8. Before moving Van de Graff aside, touch grounding rod to dome one last time to insure that dome is completely discharged.
NOTE:
- Depending on the day's humidity, discharge will be small or large.
- Internal belt and brushes remove electrons from Van de Graff dome, leaving dome positively charged. When brought in close contact, grounding rod replaces these negative charges; belt immediately strips them off again.
- Dome's potential will reach ~20,000V with respect to grounding rod.

PEDAGOGY: Remind students that excess charge distributes itself all over dome and student alike. Each strand of hair will have this same charge (positive). Thus, the strands of hair repel each other

Equipment
Van de Graff generator, control box and grounding rod; Insulating Stand, Student w/ long, oil-free hair