Electric charge is a basic property of the elementary particles of all substances. There are two types of electric charge:

1. Positive charge

2. Negative charge

The unit of charge is Coulomb (C). Similar (same sign) charges repel each other, and different (opposite sign) charges attract each other.

The electric charges obey the principle of the conservation of charge" the net electric charge in an isolated system is constant". This means when matter is created from energy, equal amounts of positive and negative charge always come into being, and when matter is converted to energy, equal amounts of positive and negative charge disappear.