Electrostatics

You need to avoid planning an electrostatics lesson and then finding that the atmosphere and the equipment are so damp that they get no effect at all, or else the results you do get appear to give the ‘wrong’ result so are confusing. There are precautions that can be taken which will usually ensure success.

All dusters used to charge objects should be freshly laundered and fluffy, and kept in a clean bag. When laundering, do not put fabric conditioner in the water as it's an anti-static agent. Students should have clean hands. Polystyrene balls, balloons, acetate and polythene rods should all be cleaned regularly. It is helpful to store all electrostatic equipment, including the Van de Graaff generator, in a cupboard which is kept warm and dry with a low wattage lamp burning. However even on a wet day, putting all the equipment near to an electric heater for some time before the lesson ensures that it is dry enough.

Today’s synthetic materials are well-known for becoming charged very easily, so that cars and carpets can give quite a nasty shock. Try separating bed-clothes in the dark of night and you will really see sheet lightning!

In modern laboratories with water fed through plastic pipes, it may be very difficult to find any point electrically bonded to earth. In such cases, an earth for electrostatics experiments can be provided by burying a substantial metal rod in the ground with a wire running through the wall to a terminal in the laboratory.

It helps to be familiar with the electrostatic series:

• Perspex (acrylic) ELECTROPOSITIVE
• Glass
• Silk
• Wood
• Sulphur
• Cotton
• Ebonite
• Indian rubber
• Polythene ELECTRONEGATIVE

If two materials are rubbed together, the material higher in the list will gain a positive charge, while the lower material will gain a negative charge.

Good luck: these lessons can be fun!