Inside a Conductor — Random Motion to Drift
A closed copper loop opened up so you can see the free electrons inside. With the field off they are already travelling at around 10⁶ m/s, colliding with the lattice and going nowhere on average. Switch the field on and a slow, steady lean appears on top of that racing — and the lean is the entire current.
Como usar esta simulação
- Press Field off to watch pure thermal motion with no current flowing
- Press Field on to superimpose the drift and start charge crossing the section
- Follow a single highlighted electron through several collisions to see its zig-zag path
- Look along the loop to confirm the drift is the same everywhere in the circuit
O que observar
- With the field off electrons move fast but the cloud as a whole stays put
- With the field on the racing is unchanged — a slow one-way lean is simply added to it
- The drift is so slow beside the thermal speed that you must watch the cloud, not one electron, to see it
- Collisions with the lattice keep resetting the acceleration, which is why the drift stays constant instead of growing
- Every cross-section of the loop carries the same drift, so the current is the same all the way round
A física por trás
Thermal speed in copper at room temperature is about 10⁶ m/s, but the directions are random, so the mean displacement is zero and no charge is transported. An applied field E adds an acceleration a = eE/m between collisions, which every collision resets. The result is a small constant average called the drift velocity, typically of order 10⁻⁴ m/s — ten orders of magnitude below the thermal speed. The current is I = nAv_d e, and only that tiny drift term appears in it.