What Electric Current Actually Is

Current is defined as I = dQ/dt: the charge passing a fixed cross section per second. That definition is about counting, not racing. Picture a wire packed solid with free electrons, like a hose already full of water. When you flip a switch, you don't wait for one electron to travel the whole wire — the electric field set up by the battery turns on everywhere in the wire at nearly the speed of light, and every electron in that crowded line starts drifting at once. The lamp lights immediately because the whole chain shoves forward together, even though each electron's own drift velocity is only millimeters per second.

Because current counts charge crossing a point, not the speed of any one charge, it depends on three things: how many charge carriers there are, how much charge each carries, and how fast they drift (I = nqvA). A thick wire with slow-moving electrons can carry the same current as a thin wire with fast ones. This is also why current is never 'used up' going around a series loop: charge cannot pile up or vanish at a resistor, so the number of electrons passing any cross section per second is identical all the way around. What a resistor uses up is energy, converting electrical potential energy to heat, while the rate of charge flow itself stays conserved.

This sets up the rest of circuits: conventional current is defined as the direction positive charge would flow, which is opposite to the actual drift of electrons, but every circuit law — Ohm's law, Kirchhoff's rules, power P = IV — is written in terms of this conventional current, so switching between the two pictures only matters for sign, never for the physics.