Superconductors

Topics: Superconductivity, Magnetic field, Magnetism Pages: 20 (6241 words) Published: May 4, 2013
SUPER CONDUCTORS
Superconductivity is an electrical resistance[->0] of exactly zero which occurs in certain materials[->1]below a characteristic temperature[->2]. It was discovered by Heike Kamerlingh Onnes[->3] in 1911. Likeferromagnetism[->4] and atomic spectral lines[->5], superconductivity is a quantum mechanical[->6]phenomenon. It is also characterized by a phenomenon called the Meissner effect[->7], the ejection of any sufficiently weak magnetic field 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 conductivity[->8] in classical physics[->9]. The electrical resistivity[->10] of a metallic conductor[->11] decreases gradually as the temperature is lowered. However, in ordinary conductors[->12] such as copper[->13] and silver[->14], this decrease is limited by impurities and other defects. Even near absolute zero[->15], a real sample of copper shows some resistance. Despite these imperfections, in a superconductor the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current[->16] flowing in a loop ofsuperconducting wire[->17] can persist indefinitely with no power source. In 1986, it was discovered that some cuprate[->18]-perovskite[->19] ceramic[->20] materials have critical temperatures above 90 K (−183 °C). These high-temperature superconductors[->21] renewed interest in the topic because of the prospects for improvement and potential room-temperature superconductivity. From a practical perspective, even 90 kelvins is relatively easy to reach with readily available liquid nitrogen[->22] (which has a boiling point of 77 kelvins), resulting in more experiments and applications.

SUPER CONDUCTORS PROPERTIES
Superconductivity is an electrical resistance[->23] of exactly zero which occurs in certain materials[->24]below a characteristic temperature[->25]. It was discovered by Heike Kamerlingh Onnes[->26] in 1911. Likeferromagnetism[->27] and atomic spectral lines[->28], superconductivity is a quantum mechanical[->29]phenomenon. It is also characterized by a phenomenon called the Meissner effect[->30], the ejection of any sufficiently weak magnetic field 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 conductivity[->31] in classical physics[->32]. The electrical resistivity[->33] of a metallic conductor[->34] decreases gradually as the temperature is lowered. However, in ordinary conductors[->35] such as copper[->36] and silver[->37], this decrease is limited by impurities and other defects. Even near absolute zero[->38], a real sample of copper shows some resistance. Despite these imperfections, in a superconductor the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current[->39] flowing in a loop ofsuperconducting wire[->40] can persist indefinitely with no power source.[1] In 1986, it was discovered that some cuprate[->41]-perovskite[->42] ceramic[->43] materials have critical temperatures above 90 K (−183 °C). These high-temperature superconductors[->44] renewed interest in the topic because of the prospects for improvement and potential room-temperature superconductivity. From a practical perspective, even 90 kelvins is relatively easy to reach with readily available liquid nitrogen[->45] (which has a boiling point of 77 kelvins), resulting in more experiments and applications. Main article: Superconductor classification[->46]

There is not just one criterion to classify superconductors. The most common are §By their physical properties: they can be Type I[->47] (if their phase transition[->48] is of first order) or Type II[->49] (if their phase transition is...
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