Electric fields

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.)