Electricity & Magnetism: Hair on End

PIRA Class: 5B10.10

Purpose:
To illustrate the electric field about a charged sphere. 

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 Graaff Generator for demo preparation and Van de Graaff operation)

In Class:

1. Locate Van de Graaff in classroom 5 feet away from any student/ student desk/ classroom electronics/ etc.

2. Choose a pacemaker-free student with oil-free, dry, med./ long hair. Have student remove any metal objects/ jewelry, especially from the side of their body that will be closest to Van de Graaff. (Small earrings are ok; Van de Graff has been known to discharge to students' metal shoe buckles.)

3. With Van de Graaff turned off, have student stand on insulating stand and place one or both hands firmly (and flatly) of Van de Graaff dome. Inform student that if they remove their hand from the dome at any time during the demonstration, they should not put it back on the dome.

4. While holding grounding rod pole in one hand, flip on belt motor at control box with the other and gradually increase belt speed.

5. Observe hair to stand on end, illustrating the electric field about the student's head.

6. Reduce belt speed then turn off Van de Graaff. 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.

7. Before moving Van de Graaff aside, touch grounding rod to dome one last time to insure that dome is completely discharged.

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

ALTERNATIVE: Use Vanessa Van de Graaff's wig - TRY THIS

Equipment:
Van de Graaff generator, grounding rod, insulating stand

Location:
Shelf 352, insulating stool is on the floor next to shelf 164