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# ''The net [[electric flux]] through a surface is proportional to the charge enclosed by the surface.'' This is a restatement of [[Gauss's law|Gauss' law]].
In some materials, the electrons are bound to the atomic nuclei and so are not free to move around but the energy required to set them free is low. In these materials, called [[Semiconductor|semiconductors]], the conductivity is low at low temperatures but as the temperature is increased the electrons gain more [[thermal energy]] and the conductivity increases.<ref>{{Cite web|title=The Feynman Lectures on Physics Vol. III Ch. 14: Semiconductors|url=https://feynmanlectures.caltech.edu/III_14.html|access-date=2020-11-26|website=feynmanlectures.caltech.edu}}</ref> Silicon is an example of a semiconductors that can be used to create [[
[[Superconductivity|Superconductors]] are materials that exhibit little to no [[Electrical resistance and conductance|resistance]] to the flow of electrons when cooled below a certain critical temperature. Superconductivity can only be explained by the quantum mechanical [[Pauli exclusion principle]] which states that no two [[Fermion|fermions]] (an electron is a type of fermion) can occupy exactly the same [[quantum state]]. In superconductors, below a certain temperature the electrons form [[boson]] bound pairs which do not follow this principle and this means that all the electrons can fall to the same [[energy level]] and move together uniformly in a current.<ref>{{Cite web|title=The Feynman Lectures on Physics Vol. III Ch. 21: The Schrödinger Equation in a Classical Context: A Seminar on Superconductivity|url=https://feynmanlectures.caltech.edu/III_21.html#Ch21-S5|access-date=2020-11-26|website=feynmanlectures.caltech.edu}}</ref>
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