Microscopic Current

How Current Forms in a Metal

Electrons already move randomly at high speed. When an electric field is applied, a tiny drift velocity is added to that random motion, producing a macroscopic current.

Electric Field

Field Off

Observation

Time x1
Average drift speed 0.000 mm/s
Thermal speed about 1.6 x 10^6 m/s
Current direction No net current

Diagram Mode

Electrons, atoms, and drift speed are exaggerated so the relationship between random motion and directed drift is visible.

Metal ions Free electrons Drift direction
Diagram: size and speed are exaggerated for teaching Current state: random thermal motion only

Key Ideas

No electric field

Electrons move rapidly in every direction. Higher temperature increases this random thermal speed, but the average velocity in any direction is still about zero.

With an electric field

Electrons still move randomly, but a very small drift velocity is added opposite the field. Conventional current points opposite electron drift.

Real-scale mode

The scale uses copper-like values: atomic radius about 1.28 x 10^-10 m and nuclear radius about 4.8 x 10^-15 m, so the nucleus radius is about 1/27,000 of the atomic radius.