Electric Current

Electric current is the movement of mobile charge carriers. It is measured in amperescoulombs per second. With positive and negative charge carriers we have to take into consideration the total charge going in each direction. So, if we have a conductor with:

then for positive charge we have:


coulombs of charge passing a point in one second. Similarly for negative charge we have:


This gives us in total:

Q++Q- = (qpnpvp + -qnnn-vn)ΔtA

Now, current is the rate of charge flow, so:

I = (Q++Q-)/Δt = (qpnpvp + -qnnn-vn)A

Note that in a metal, we only have one type of mobile charge carrier, the electron, so:

I = Q-/Δt = -qnnn-vnA

The current divided by the area (I/A in our notation) gives us what is known as the current density.


Fischer-Cripps. A.C., The Electronics Companion. Institute of Physics, 2005.