In terms of this definition, one coulomb is the charge
flowing through a wire in 1 s if the current is 1 A (ampere), (see Chapter 1
of Class XI, Physics Textbook , Part I) In this system, the value of the
basic unit of charge is
e = 1 602192 × 10–19 C
Thus, there are about 6 × 1018 electrons in a charge of  –1C In
electrostatics, charges of this large magnitude are seldom encountered
and hence we use smaller units 1 mC (micro coulomb) = 10–6 C or 1 mC
(milli coulomb) = 10–3 C