The charge on any body can be expressed as an integral multiple of basic unit of charge, i.e. charge on one electron. This phenomena is called quantisation of electric charge. It can be written as q = ± ne.
where, n = l, 2, 3, ••• is any integer, positive or negative and e is the basic unit of charge.
Charge is said to be quantised because it can have only discrete values rather than any arbitrary value, i.e. free particle has no charge at all or a charge of+10 e or —6 e but not a free particle with a charge of, say 3.57 e.
(ii) In practice, the charge on a charged body is very large. On the other hand, the charge on an electron is very small. When electrons are added to a body or removed from a body, the change taking place in the total charge on the body is so small that the charge seems to be varying in a continuous manner. Therefore, quantisation of electric charge can be ignored, when dealing with a large scale charged body.