demonstrations:van_de_graaff_human_chain
Van de Graaff Human Chain
Materials: ★★☆ Available in most school laboratories or specialist stores
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: Passing the Charge
Summary
When people form a chain holding hands, with one person touching the dome of a Van de Graaff generator, the charge spreads through every person in the chain. If the last person in the line brings their free hand near a grounded object, all people in the chain receive a shock.
Procedure
- Place the Van de Graaff generator in an open area with space for several volunteers.
- Have one volunteer stand on an insulating platform and place their hand on the generator’s dome.
- Ask several other volunteers to form a chain by holding hands with the first person, all being insulated from the floor (e.g. on tables or plastic mats).
- Turn on the generator and allow charge to build up.
- Have the last person in the chain carefully bring their free hand near a grounded rod or a metal object.
- Observe the spark as the chain discharges.
- After the demonstration, turn off the generator and discharge the dome with the grounding rod before anyone lets go.
Links
Physics -2018 - Van der Graaf chain - Clink's Class:
Physics 2021 - (2nd period) - The Big Shock - Clink's Class:
Variations
- Try different numbers of people in the chain to see how far the charge can travel.
- Perform in a darkened room to make sparks more visible.
- Compare the effect with everyone standing on insulating mats versus standing on the floor.
Safety Precautions
- Always discharge the dome with a grounding rod before anyone breaks the chain.
- Ensure participants are not wearing or carrying sensitive electronics (phones, watches, hearing aids, pacemakers).
- Warn participants that small shocks and sparks may be startling.
- Use only healthy volunteers and avoid individuals with heart conditions or electronic medical implants.
Questions to Consider
- How does the charge travel from the generator through the human chain?
- Why does the spark appear at the last person when they approach a grounded object?
- What role does the insulating platform play in this demonstration?
- How is this related to how electricity flows in circuits?
- What similarities exist between this demonstration and natural lightning discharges?