Static Charge Demo Guide
Estimate the capacitance and charge of a charged sphere, and walk through classic static-electricity demonstrations with low-voltage safety notes.
Estimated charge
Three demonstrations to try
Balloon and hair. Rub an inflated balloon briskly on dry hair for about 20 seconds, then slowly pull it away. The balloon picks up a negative charge from the friction (the triboelectric effect), and it will make hair stand up or stick lightly to a wall for a few minutes.
Electrophorus.Rub a charged insulating plate (like a PVC sheet) with fur or wool, then lower a metal disc with an insulated handle onto it. Touching the disc briefly grounds one side, and lifting it away leaves the disc charged — a 180-year-old device that can recharge itself repeatedly from a single rub.
Van de Graaff generator.A small, hand-cranked or motor-driven tabletop unit charges a metal dome to a high voltage at extremely low current. Touching the dome while standing on an insulated stool is the classic hair-raising demonstration — always follow the manufacturer’s instructions and supervise young students.
Frequently Asked Questions
How is the charge on a sphere calculated?
An isolated conducting sphere behaves like a capacitor, with capacitance C = 4πε₀r (r is the radius in metres, ε₀ is the permittivity of free space). Once you know the capacitance and the voltage it's charged to, the stored charge follows from Q = C × V.
Why can a Van de Graaff generator reach tens of thousands of volts safely?
The generator's belt moves only a tiny amount of charge at a time, so even though the voltage is very high, the current is minuscule and the total energy released in a spark or a touch is small — similar to why a small static shock from a doorknob doesn't hurt despite being thousands of volts. High voltage at very low current is the key safety factor in these classic demonstrations.
What are some classic static-electricity demonstrations?
Rubbing a balloon on hair and sticking it to a wall, an electrophorus (a charged plate that transfers charge to a metal disc by induction), a Van de Graaff generator making hair stand on end, and a simple electroscope showing charge by the separation of two thin foil leaves are all standard, well-documented classroom demonstrations of static electricity.
What is the triboelectric effect?
It's the transfer of electrons between two different materials when they're rubbed together or separated — one material ends up with a surplus of electrons (negatively charged) and the other with a deficit (positively charged). Balloon-on-hair, rubbing a plastic rod with fur or silk, and walking across a carpet are everyday examples.
Educational estimate for classroom-style static-electricity demonstrations only — this is not a safety certification. Use only commercially manufactured demonstration equipment, follow its instructions, and have an adult or instructor supervise. This guide covers static electricity only and has no connection to skin conductance or any medical measurement.