It is possible to transfer electrons from one material to another owing to their position the atom. In some materials (metals), electrons are free to move inside them.

Materials in which electrons can move through easily are called electrical conductors.

Some materials are good electrical conductors while others are poor electrical conductors.

Examples of good electrical conductors include all metals (e.g. copper, silver, aluminium, mercury, etc) and carbon graphite. Meanwhile examples of poor electrical conductors include; human body, the earth, semiconductors at room temperature, water, moist air, etc.

Materials in which electrons cannot move through are called electrical insulators.

Examples include rubber, plastics, Perspex, polythene, glass, dry air, cotton, wool, cellulose acetate, etc.

CHARGED MATERIALS

Charging a material means making the material to either gain or lose electrons.

Most materials around · us are neutral. That is, they have the same number of protons and electrons.

On the other hand, a charged material has either more protons than electrons or more electrons than protons. There are two types of charged materials; positively charged materials and negatively charged materials.

• A positively charged material contains more protons than electrons. If a neutral material happens to lose electrons, it becomes positively charged as it will now contain more protons than electrons.
•  A negatively charged material contains more electrons than protons. So if a neutral material gains electrons, it becomes negatively charged (more electrons than protons)

The net charge (Q) acquired by a body either due to excess electrons or a proton is given by;

                                                   Q = ne

Where n = number of excess protons or electrons, e-1. 6×10^-19 C [charge on a proton (+) or an electron (-)]

The net charge on a neutral body is zero.

Force between charged materials

Experiments have shown that there is a force (electrostatic force) between charged objects

The electrostatic force between two materials is attractive if they carry different kinds of charges [(-) and (+)]. Meanwhile the force is repulsive if they carry the same kind of charge [(-) and (-) or (+) and (+)] ·

This result is usually stated as:

The electrons in an atom are held in the electronic shells by the electrostatic force attracting them towards the positive nucleus.

The magnitude of the force between two charged objects depends on

• The distance between the objects; the closer the objects are, the stronger the force.
• The quantity of charge on each body; the larger the quantity of charge on each body, the stronger the force.

If two charged particles carrying charges Q₁ and Q₂ respectively are separated by the distance r, then the relationship between the forces (F), Q₁, Q₂ and r can be written as

                                      F α =

The above relationship is usually referred to as Coulomb's Law.

Experiment to demonstrate the basic law of electrostatics

The charged rods are suspended as shown. It is observed that repulsion occurs between rods carrying the same kind of charge. Meanwhile attraction occurs with rods carrying different kinds of charge.

Hence like charges repel, unlike charges attract.