Could someone explain mean free electron paths with regard to; Drude model and Fermi velocity I have answered a question where you are given relaxation time and fermi velocity at 4K and 300K and asks you to work out the mean free path. Easy. Next it says how do these values compare with what the Drude model predicts. I keep reading that Drude neglects electron electron interactions, does this mean that they can still scatter off each other but only on head on collisions? It also says that electron ion interactions are neglected except in head on collisions, but that in Fermi, (I assume this is the Fermi model?) electrons only don't scatter off ions in a perfect periodic lattice. My main question is; does the Drude model give a longer electron mean free path than the Fermi model, and if so, why?