Editing Mean free path (section)

===Electronics===
{{See also|Ballistic conduction}}

In macroscopic charge transport, the mean free path of a [[charge carrier]] in a metal <math>\ell</math> is proportional to the [[electrical mobility]] <math>\mu</math>, a value directly related to [[electrical conductivity]], that is:
:<math>\mu = \frac{q \tau}{m} = \frac{q \ell}{m^* v_{\rm F}},</math>

where ''q'' is the [[elementary charge|charge]], <math>\tau</math> is the [[mean free time]], ''m<sup>*</sup>'' is the [[Effective mass (solid-state physics)|effective mass]], and ''v''<sub>F</sub> is the [[Fermi velocity]] of the charge carrier. The Fermi velocity can easily be derived from the [[Fermi energy]] via the non-relativistic kinetic energy equation. In [[thin film]]s, however, the film thickness can be smaller than the predicted mean free path, making surface scattering much more noticeable, effectively increasing the [[resistivity]].

[[Electron mobility]] through a medium with dimensions smaller than the mean free path of electrons occurs through [[ballistic conduction]] or ballistic transport. In such scenarios electrons alter their motion only in collisions with conductor walls.