Drift velocity

Definition

Drift velocity is the average velocity at which free charge carriers, such as electrons, move through a conductor under the influence of an electric field. It is typically much smaller than the speed of individual electrons due to frequent collisions within the material.

5 Must Know Facts For Your Next Test

1. Drift velocity ($v_d$) is given by the formula $v_d = \frac{I}{nAq}$, where $I$ is the current, $n$ is the number of charge carriers per unit volume, $A$ is the cross-sectional area of the conductor, and $q$ is the charge of an electron.
2. The direction of drift velocity for electrons in a conductor is opposite to the direction of the electric field because electrons are negatively charged.
3. Drift velocity is typically on the order of millimeters per second (mm/s) in practical conductive materials.
4. Ohm's Law can be used to relate drift velocity to other quantities: $V = IR$, where $V$ is voltage, $I$ is current, and $R$ is resistance.
5. An increase in temperature generally increases atomic vibrations in a conductor, leading to more collisions and thus reducing drift velocity.

Review Questions

• What factors influence drift velocity in a conductor?
• How does drift velocity relate to electric current and charge carrier density?
• Why does increasing temperature generally reduce drift velocity?

Related terms

Electric Current: The flow of electric charge through a conductor; measured in amperes (A).

Resistance: A measure of how much a material opposes the flow of electric current; measured in ohms (Ω).

Ohm's Law: $V = IR$, which states that voltage across a resistor is directly proportional to current through it.