3  Quantisation of charge
Experimentally it is established that all free charges are integral multiples
of a basic unit of charge denoted by e Thus charge q on a body is always
given by
q = ne
where n is any integer, positive or negative This basic unit of charge is
the charge that an electron or proton carries By convention, the charge
on an electron is taken to be negative; therefore charge on an electron is
written as –e and that on a proton as +e