Editing Electric current (section)

===Superconductivity===
{{Main|Superconductivity}}

Superconductivity is a phenomenon of exactly zero [[Electrical resistance and conductance|electrical resistance]] and expulsion of [[magnetic field]]s occurring in certain materials when [[cryogenics|cooled]] below a characteristic [[Critical point (thermodynamics)|critical temperature]]. It was discovered by [[Heike Kamerlingh Onnes]] on April&nbsp;8, 1911 in [[Leiden]]. Like [[ferromagnetism]] and [[atomic spectral line]]s, superconductivity is a [[quantum mechanics|quantum mechanical]] phenomenon. It is characterized by the [[Meissner effect]], the complete ejection of [[magnetic field|magnetic field lines]] from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of ''[[perfect conductor|perfect conductivity]]'' in [[classical physics]].