Spark image

Electric fields

You can feel the hairs on your hand standing up if you are near a Van de Graaff generator
You hear crackling and may fell tingling if you stand below a high voltage power line
A spark can be made to jump between two parts of a sparking plug
Lightning flashes occur between a cloud and the ground
In a plasma globe there are writhing lines of light
The carbon powder in a photocopier is attracted to the master disc

These effects are all due to the presence of an electric field.

In just the same way that a magnet has a magnetic field surrounding it so electric charges have an electric field surrounding them. If two electrodes with a high voltage between them are placed in a shallow dish of castor oil an electric field will exist in the non-conducting oil.

You can show the shape of the field lines by sprinkling rice or semolina on the surface of the oil in just the same way that you would use iron filings to show the shape of a magnetic field.

The fields that you would get for four important arrangements are shown in the diagrams:
1. Two unlike charges attraction.
2. Two like charges repulsion.
3. A charge and an oppositely charged plate.
4. Two oppositely charged plates.

(The direction of the arrows shows the way a positive charge would move if placed in the field.)

© Keith Gibbs 2020