Conservation of electric charges:
Electric charges (quantity of electricity) is conserved in the same manner as linear momentum, energy, angular momentum etc. The law of conservation of charge is the basis of many equations of electricity and magnetism. According to the law of conservation of electric charge, the algebraic sum of positive and negative charges in an isolated system remains constant. Conservation of charge does not mean that charge cannot be produced or destroyed. It simply means that if ever charge is created or destroyed, it will always be in equal and opposite amounts. For example, when two bodies are rubbed, we get simultaneously two unlike charges of equal magnitudes.
Quantization of electric charge:
It is proved from number of experiments that all charges occurring in nature are positive or negative integral multiples of certain minimum electric charge. This minimum electric charge is the magnitude of electric charge on an electron. This fundamental charge to which we give the symbol e, has the magnitude 1.60210 x 10-19 coulomb. So, the charge on an electron is -e while the charge on a proton is +e. The fact that charges on a proton and on an electron are numerically equal but opposite in sign has been checked experimentally to an amazing degree of accuracy namely to one part in 1020.
Any charge q, is given by
q = ne
where n = 1, 2, 3, ....
When a physical quantity such as electric charge exists in discrete 'packets' rather than in continuous amount, it is said to be quantised. This fact is referred to as quantisation of electric charge. When suitably examined on a microscopic scale, most of the properties such as mass, energy, angular momentum are observed to be quantised.
Additive nature of charge: The total electric charge of a body is equal to the algebraic sum of all the electric charges located anywhere on the body. While taking algebraic sum, due consideration has to be given to + or – signs. If two charges +2q and +3q are taken, then the total charge is +2q + 3q or +5q. Similarly, if two charges +2q and –3q are taken, then the total charge is +2q – 3q or –q.