Topic explanation

Standard explanation

Drift velocity is the average velocity acquired by charge carriers in an applied electric field.

Key points

• Drift velocity is the average velocity acquired by charge carriers in an applied electric field.
• Without a field, random carrier motion averages to zero and produces no net current.
• Electrons drift opposite to the electric field and conventional current.
• In time Δt, carriers sweep through volume AvdΔt.
• The current magnitude is I=nqAvd.
• Drift speed is vd=InqA.
• Current density is J=IA=nqvd.
• A circuit responds quickly even though individual electron drift is slow.

Labelled diagram