Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Clearing smoke

Demonstration

A demonstration of the principle of electrostatic precipitation.

Apparatus and materials

Van de Graaff generator

Transparent plastic cup (e.g. Perspex picnic cup)

Drawing pin

Aluminium foil

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. 


Procedure


Generator and cupa 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.
 

Teaching notes


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 
 

Related guidance


Electrostatics

Van de Graaff Generator - the basics