Electron Theory. The basis of our understanding of electricity is the electron theory. This theory states that all matter, that is, everything that occupies space and has weight, is composed of tiny invisible units called atoms. Atoms, in turn, are subdivided into still smaller particles called protons, neutrons, and electrons. The protons and neutrons make up the central core, or nucleus, of the atom, while the electrons spin around this central core in orbits as illustrated in Fig. 1.1.

Figure 1.1: Typical atom consisting of nucleus and revolving electrons. The nucleus is composed of protons and neutrons. The protons carry a positive electrical charge, the electrons carry a negative electrical charge, and the neutrons are neutral; that is, they carry neither a positive nor a negative charge

The protons and electrons are charged with small amounts of electricity. The proton always has a positive charge of electricity on it, while the electron has a small negative charge. The magnitude of the total positive charge is equal in amount to the sum of all the negative charges on all the electrons. The neutron has no charge on it, either positive or negative, and is therefore neutral and hence called neutron.

Atoms differ from one another in the number of electrons encircling the nucleus. Some atoms have as many as 100 electrons spinning around the nucleus in different orbits. The atom of hydrogen gas has only 1 electron. The atom of lead has 82 electrons.

Positive and negative charges of electricity...