Electric current I = $\frac{dQ}{dt}$ is the rate of charge flow. SI unit: ampere (A), a base SI quantity. Conventional current flows from high to low potential (positive charge flow direction), opposite to electron drift. Current density J = $\frac{I}{A}$ = $nev_d$, where n = number density of free electrons (~10^28 /$m^3$ for copper), e = 1.6 x 10^(-19) C, $v_d$ = drift velocity. The drift velocity $v_d$ = eE*tau/$m_e$, where tau is the relaxation time (~10^(-14) s) and E is the applied electric field. Typical $v_d$ ~ 10^(-4) m/s — electrons drift slowly but the electric signal propagates at nearly c because the field establishes almost instantaneously throughout the conductor.