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.
