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.
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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.
The direction of drift velocity for electrons in a conductor is opposite to the direction of the electric field because electrons are negatively charged.
Drift velocity is typically on the order of millimeters per second (mm/s) in practical conductive materials.
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.
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?