Editing mean free time

{{title|Mean Free Time}}
'''Mean free time''' or '''conductivity relaxation time''' (<math>\tau</math>) is the average time between scattering events. For example, the average time between collisions in a [[semiconductor]].

=== Relation to mean free path ===
The [[mean free path]] is the average distance the electron travels between collisions. In other words, it is the average distance the electron travels in <math>\tau</math> time.

:<math>\lambda = \langle v \rangle \tau</math>


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 {{title|Mean Free Time}}
-'''Mean free time''' or '''collision time''' or '''conductivity relaxation time''' (<math>\tau</math>) is the average time between scattering events. For example, the average time between collisions in a [[semiconductor]].
+'''Mean free time''' or '''conductivity relaxation time''' (<math>\tau</math>) is the average time between scattering events. For example, the average time between collisions in a [[semiconductor]].
-== Overview ==
-[[Charge carriers]] in a material are in random thermal motion with average velocity <math>\langle v \rangle</math>. When an electric field <math>E</math> is applied, the carriers acquire [[drift velocity]] <math>v_d</math> in the same direction, opposite to the field. Constant collisions with lattice ions means that the the gained kinetic energy is lost pretty frequently. The '''mean free time''' <math>\tau</math> is the average time before a randomly picked electron makes it next collision. Note that collisions are random, so <math>\tau</math> does not depend on the elapsed time since prior collision.
 === Relation to mean free path ===