Clearing smoke

Demonstration

A demonstration of the principle of electrostatic precipitation.

Apparatus and Materials

• Transparent plastic cup (e.g. Perspex picnic cup)
• Drawing pin
• Aluminium foil
• Smoke source (e.g. paper drinking straw)

• Van de Graaff generator

Health & Safety and Technical Notes

Read this comprehensive safety note:

• Van de Graaff generator safety

• Read our standard health & safety guidance

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.

Procedure

1. Place the cup on top of the machine's sphere. Connect its lid to earth.
2. Place a drawing pin, point upwards, in the cup. This will ensure a strong local electric field, and ‘electric wind’ to stir the smoke.
3. Fill the cup with smoke and run the machine.

Teaching Notes

• 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.
• 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

• A video showing how to use a Van de Graaff generator: