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mean free path

(average length that a particle travels before interaction)

The term mean free path is used in the physics of moving particles (atoms, electrons, photons, etc.) to indicate the average length they travel between interactions. When performing calculations in a substance where some type of particle moves around, estimates of the consequences can be calculated by assuming all the particles always move the same distance between interactions, using the mean free path as that distance. The mean free path can be determined from density and the radius at which the particles interact.

Some situations where it is used:

Further reading:

Referenced by pages:
cross section
optical depth (τ)
Rosseland mean opacity