This demonstration is an example of electrostatic precipitation, where electrostatic charge is used to attract smoke particles. This demonstration has real life applications. In some factory smoke towers, an electrostatic charge is created which ensures much of the smoke produced is attracted to collection chambers in the wall of the chimney, rather than pumped into the atmosphere.
The electrostatic precipitator in this case is a clear plastic tumbler which is placed on the dome of a Van Der Graff generator. By earthing part of the tumbler, an electric field is created between the top and bottom contacts and the smoke particles are attracted to the top of the cup.
Equipment required (per demo):
- Van Der Graff generator
- Plastic beaker
- Aluminium foil
- Drawing pin
The electrostatic precipitator needs to be constructed as in Fig 1. A solid plastic tumbler needs to have a hole drilled into its base, through which a large screw should be inserted. On the inside bottom, a small layer of aluminium foil should be placed. This needs to make electrical contact with the screw.
When the tumbler is placed onto the Van Der Graff dome, the screw head needs to make electrical contact with it. A layer of aluminium foil should be placed over the open top of the tumbler. This will act as the other contact and needs to be connected to earth. This can be achieved by attaching a crocodile clip and length of wire to it with the free end connected to earthed metalwork (such as a pipe) in the lab.
A match is lit, blown out and quickly placed into the bottom of the tumbler. The Van Der Graff generator is turned on and as the charge builds, the smoke from the spent match should start moving towards the top of the cup.