A continuous and closed path of an electric current is called an electric circuit. An electric circuit consists of electric devices, source of electricity and wires that are connected with the help of a switch.
The unit of electric current is ampere (A). 1 A is defined as the flow of 1 C of charge through a wire in 1 s.
One electron possesses a charge of 1.6 ×10-19 C, i.e., 1.6 ×10-19 C of charge is contained in 1 electron.
∴ 1 C of charge is contained in 1 / 1.6 x 10-19
= 6.25 x 1018 = 6 x 1018
Therefore, 6 x 1018 electrons constitute one coulomb of charge.
Any source of electricity like battery, cell, power supply, etc. helps to maintain a potential difference across a conductor.
If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.