What are the main sources of electrical resistance in a metal?
The factors that affect the electrical resistance of a metal are impurity, temperature and alloying. The free mean path of an electron is the mean distance it travels between successive collisions. For an ideal crystal with no impurities and imperfections the mean free path at 0 K s infinite. That is, there are no collisions and the electrical conductivity is ideally infinite. Introduction of solute atoms into the crystal results in collisions, reducing the mean free path and the conductivity.