A demonstration of the principle of electrostatic precipitation.
Apparatus and materials
Transparent plastic cup (e.g. Perspex picnic cup)
Smoke source (e.g. paper drinking straw)
Health & Safety and Technical notes
Read this comprehensive safety note.
Drill a hole in the bottom of the cup. Run a bare wire through the hole to make contact with the Van de Graaff’s dome. Place a small piece of foil at the bottom of the cup, to make contact with the wire. Place a metal lid of foil on top of the cup.
A video demonstration of the Van de Graaff generator is available at the National STEM Centre eLibrary.
a Place the cup on top of the machine's sphere. Connect its lid to earth.
b Place a drawing pin, point upwards, in the cup. This will ensure a strong local electric field, and ‘electric wind’ to stir the smoke.
c Fill the cup with smoke and run the machine.
1 The electric field between the top and the bottom of the container clears the container of smoke as the particles are attracted to the top.
2 This principle is used in clearing smoke in a factory chimney. There is a wire down the centre of the chimney and a potential difference between the wire and the chimney walls. The smoke particles collect on the walls and so do not escape into the atmosphere.
This experiment was safety-tested in April 2006