Electronic Circuits: Current

The current is basically a charge passing through an area A over a specific unit of time. It is denoted by ΔQ/ΔT. 

We can define a symbol, I as an instantaneous current where I = lim (as Δt -> 0) ΔQ/Δt which is equivalent to dQ/dt at any point. Current is measured in Amps, which is basically 1 coulomb per second. This diagram shows a good illustration of current. 

Electrons go the opposite the direction of currents, so we can assume that the current is the proton moving, even though only valence electrons will jump and move due to polarity changes, so basically the current is free electrons moving through the ions. 

Now the charge is measured in Coulombs. In one electron there are -1.602 * 10 ^ (-19) Coulombs. This means that in one coulomb, there are -6.24 * 10 ^(18) electrons since we just reversed the -1.602 * 10 ^ (-19) number. Conversely, there are 1.602 * 10 ^ (-19) Coulombs in one proton and 6.24 * 10 ^(18) protons in 1 coulomb. We can represent the 1.602 * 10 ^ (-19) and -1.602 * 10 ^ (-19) as Qp and Qe, respectively. Remember since the current is the charge over time, charge can equal to current multiplied time, or ΔQ = ΔI x T.