> Electrical current is the movement of electrons from negatively charged atoms to negatively charged atoms when an appropriate external force is applied.
So current is the flow of electrons. Charge is the quantity that flows. Current exists because of the [first law of electrostatics](/Electronics/Physics_of_electricity/Coulombs_Law.md).
When there is an excess of electrons at one terminal (i.e. negatively charged atoms) and a deficiency of electrons at the other terminal (i.e. positively charged atoms), a difference of potential exists between the two terminals.
When the terminal are connected to each other via a conductor (e.g. copper wire) electrons will flow along the conductor. This is provided that there is a source to supply electrons at one end and remove them at the other. This is **voltage source**.
_The diagram below illustrates the flow of current where the circles are electrons knocking into each other to generate current:_
## Formal expression
We measure **charge** in Coulombs ($C$). A Coulomb is an aggregate of the charge of thousands of electrons because their individual charge is so small.
One Coulomb is equal to the charge of $6.24 \cdot 10 ^{18}$ electrons.
