What is responsible for the electric resistance R? At the beginning of the 20th century, people thought it was the collisions of the electrons against the surrounding atoms. But quantum physics has proved that electrons are waves whose shape adapts to the regular pattern formed by the atoms. It enables the electron to move without being impeded by the atoms, even if the latter take a lot of space and almost touch one another. It is the flaws in the pattern regularity which disrupt the electrons and provoke the collisions.
Such flaws include a missing atom (a vacancy), one too many of them (interstitial atom), and a bigger atom or a smaller one (an impurity). Every time such disorder happens, the electron, as a wave, bounces off and hence slows down, like a wave in the sea bouncing off a pier.
Another source of chaos, the most significant as far as pure metals are concerned, comes from the vibrations of the atoms due to the thermal agitation. These vibrations also create a kind of chaos, like calm pupils sitting in a classroom who suddenly start fidgeting right before recess. The higher the temperature, the more the atoms vibrate, and the more significant the chaos.
Hence, in a metal, the electric resistance comes from the vibrations of the atoms and the impurities or the flaws in the atom pattern. A simple experiment can prove it: if you cool a metal, it conducts electricity much better. Indeed, its atoms vibrate less and do not impede the electrons..
