15.2 Conductors and insulators  (Page 39/3)

Conductors and insulators

All atoms are electrically neutral i.e. they have the same amounts of negative and positive charge inside them. By convention, the electrons carry negative charge and the protons carrypositive charge. The basic unit of charge, called the elementary charge, e , is the amount of charge carried by one electron.

All the matter and materials on earth are made up of atoms. Some materials allow electrons to move relatively freelythrough them (e.g. most metals, the human body). These materials are called conductors .

Other materials do not allow the charge carriers, the electrons, to move through them (e.g. plastic, glass).The electrons are bound to the atoms in the material. These materials are called non-conductors or insulators .

If an excess of charge is placed on an insulator, it will stay where it is put and there will be a concentration of charge inthat area of the object. However, if an excess of charge is placed on a conductor, the like charges will repel each otherand spread out over the outside surface of the object. When two conductors are made to touch, the total charge on them is shared between thetwo. If the two conductors are identical, then each conductor will be left with half of the total charge.