Definition

Electric current is the flow of tiny charged particles, usually electrons, through a wire, much like water flowing through a hose except it is charge that moves, and current needs a complete loop: cut the wire anywhere and the flow stops everywhere, just as a broken hose stops delivering water. It is the rate of flow of electric charge through a conductor, measured in amperes, one ampere being one coulomb of charge per second, and by Ohm's law $I = V/R$; in metals the moving charges are electrons, though conventional current is drawn in the direction positive charge would move. Formally, $I = dQ/dt$, and in a conductor with charge-carrier density $n$, carrier charge $q$, cross-section $A$, and drift velocity $v_d$, it equals $I = nqAv_d$; the microscopic form of Ohm's law is $\vec{J} = \sigma\vec{E}$, current dissipates power $P = I^2R$ as Joule heating and generates a magnetic field described by Ampere's law, the basis of electromagnets and motors, and Kirchhoff's current law states that current into a junction equals current out, a consequence of charge conservation.