demonstrations:van_de_graaff_levitating_foil
Van de Graaff Levitating Foil
Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff
Categories: Van de Graaff Generator
Alternative titles: Electrostatic Spinning Strips
Summary
Thin strips of aluminum foil can be levitated and made to spin near the charged dome of a Van de Graaff generator. The electrostatic field induces a dipole in the strip, while ionic wind from the generator provides lift and rotation, creating a dramatic and attention-getting demonstration.
Procedure
- Cut strips of aluminum foil about 50 mm long, 2.5 mm wide, and 0.02 mm thick.
- Charge a Van de Graaff generator so that its dome is strongly electrified.
- Bring a foil strip near the dome, aligned with the electric field lines.
- Observe as the foil strip levitates at a distance of about 15 cm from the dome.
- The strip spins due to a combination of induced dipole attraction and ionic wind streaming from the dome.
- Try releasing several strips around the dome to see multiple spinners levitate simultaneously.
Links
Electrostatic levitation using Van de Graaff generator - dizekat:
van der Graaff levitating aluminium foil - PhysicsExperiments.org:
Variations
- Use different sizes, shapes, or twists of foil strips to compare rotation speeds and stability.
Safety Precautions
- Do not touch the Van de Graaff dome while it is operating.
- Keep electronic devices away from the generator to avoid damage from static discharge.
- Ensure foil strips are lightweight and free of sharp edges.
Questions to Consider
- Why do the foil strips first attract to the dome and then stabilize at a distance? (Electrostatic attraction competes with repulsion from ionic wind, producing balance.)
- What causes the strips to spin? (Slight twists in the foil interact with the ionic wind, creating torque.)
- How is this related to the behavior of other lightweight objects in strong electric fields, like the “Orbiting Foil” demonstration?
- What role does the electric dipole moment play in the attraction of the foil strips?