#### fluidistic

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In reality, in metals at least, only electrons that have an energy near the Fermi energy can conduct electricity. That's because they are the only ones that can get accelerated by an applied electric field since the lower energy electrons cannot increase their energy due to the already occupied states and they have to follow the Pauli exclusion principle, being fermions. This can be seen with the Fermi-Dirac distribution. As as a result, the ##n## value that can be computed this way is much smaller than the one that comes from Drude's model (around 3 orders of magnitude smaller for Cu at 300K according to some calculations on the Internet).

On hyperphysics (http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/Fermi2.html) they show a formula to compute ##n## which is valid at 0K. The moral of the story is that it indeed involves dealing with the Fermi-Dirac statistics, unlike what the Drude's model does.

Therefore, I can understand what the ##n## coming from Fermi-Dirac statistics is, but not the one coming from Drude's model. They seem to differ by several orders of magnitude. Can someone explain what the ##n## coming from the Drude model physically represents?