Unit Of Charge And Current.

• Each electron carries the same amount of negative charge and we could use the charge on a single electron as the unit of charge. 
• However, the charge on an electron is tiny and electric currents contain many electrons flowing through a wire. 
• The unit of charge is thus the coulomb (C) and one coulomb is approximately equal to the total charge of six million million million electrons (to be more exact the charge on one electron is 1.6x10-19, therefore 1C comprises the charge of 6.25x1018 electrons). 
• If electrons flow past a point on a wire so that 1 coulomb of charge passes every second, a current of one ampere (A) is said to flow. 
• Therefore, electrical current is the rate at which charge passes through a wire. Mathematically we can say:

Where:
Q = the charge transferred in coulombs (C)
I = the current in amperes (A)
t = time during which the current flows in seconds (s)