Current, charge flow and drift velocity

Repair the common break

Common misconception: Drift velocity is the signal speed around a circuit.

Correct model: Current is charge flow rate and I = nAvq relates microscopic carrier drift to the macroscopic current.

Worked transfer

For carrier density n, cross-section A, charge q and drift speed v, the charge crossing in time t is nAvtq, giving I = nAvq. This slow drift is not the circuit signal speed.

Guided practice

Explain why “Drift velocity is the signal speed around a circuit.” fails. Then construct one example that correctly applies current, charge flow and drift velocity.

Independent practice

Find the drift speed in a 1.0 mm² wire carrying 2.0 A if n = 8.5 × 10²⁸ m⁻³ and q = 1.60 × 10⁻¹⁹ C.

Return to the recorded repair plan when the explanation and application are secure enough to re-test.