Drift velocity

Definition

Drift velocity is the average velocity of free electrons in a conductor due to an applied electric field. It is typically very small, on the order of millimeters per second.

5 Must Know Facts For Your Next Test

1. Drift velocity is directly proportional to the applied electric field and inversely proportional to the resistivity of the material.
2. The formula for drift velocity is $v_d = \frac{I}{nAe}$, where $I$ is current, $n$ is charge carrier density, $A$ is cross-sectional area, and $e$ is charge of an electron.
3. Drift velocity in a conductor increases with increasing current or decreasing cross-sectional area.
4. Even though individual electrons move rapidly in random directions, their net movement due to drift velocity is much slower.
5. In metals, drift velocity explains how electrical energy is transmitted through the motion of electrons.

Review Questions

• What factors affect drift velocity in a conductor?
• How does increasing the cross-sectional area of a wire affect its drift velocity for a constant current?
• Derive the formula for drift velocity using known quantities like current and charge carrier density.

Related terms

Electric Field: A region around a charged particle where other charged particles experience a force.

Resistivity:

A measure of how strongly a material opposes the flow of electric current, denoted by $\rho$.

Charge Carrier Density:

The number of charge carriers (usually electrons) per unit volume in a material.