Drift velocity
The average velocity at which charge carriers move through a conductor in response to an applied electric field. Despite its slowness (typically mm/s for electrons), drift velocity is related to current by I = nAve where n is carrier density, A is cross-section, ve is drift velocity, and e is charge.
Formula
I = nAve
Real World
In the copper wiring of a household kettle (2 kW, 230 V), electrons drift at roughly 0.1 mm/s — slower than a snail — yet the kettle heats almost instantly because the electric field propagates at near light speed.
Exam Focus
When comparing wires, use I = nAve to reason about which variable changes; show your substitution explicitly for 'show that' questions.
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