21. Many other mean free paths can be defined. 22. This leads to a mean free path 23. The mean free path " ? " is the average distance traveled by electrons before their collisions. 24. Thus, if the electrical conductivity is low, the mean free path of the electrons is very short. 25. Copper nanowires less than 40 nm wide will shorten the mean free path to the wire width. 26. Sometimes one measures the thickness of a material in the " number of mean free paths ". 27. Because of spectrum hardening, the " mean free path " of the X-ray spectrum changes with distance. 28. In fact, the kinetic diameter of a molecule is defined in terms of the mean free path . 29. When " L " is larger than the phonon mean free path , Umklapp scattering process limits thermal conductivity. 30. At Lower Rainham the route heads into Riverside Country Park and follows traffic-free paths beside the River Medway.
