Projekt In Danish Conserning Superconductivity Essay

2793 words - 11 pages

FormålTeoriDette fysik projekt har til formål at undersøge supraledning og belyse dets anvendelsesmulighed til transport i nutiden og fremtiden. Et bestemt materiales supraledende evne, vil blive undersøgt ved et laboratorieforsøg. Om dette materiale har nogen modstand ved meget lave temperaturer, vil også blive undersøgt ved et forsøg. Hvad er supraledere og supraledning?Næsten alle metallers resistans vokser lineært med temperaturen. Ved nedkøling af bestemte materialer til det absolutte nulpunkt, har det vist sig at resistansen falder til nul, samtidig med at de frastøder magnetfelter. Det er stoffer med disse egenskaber, man kalder supraledere og egenskaben kaldes supraledning.Historisk baggrundDet var den hollandske fysiker H. Kamerlingh-Onnes der i 1911 opdagede fænomenet "supraledning". Han havde fundet en måde at fortætte Helium på, dette brugte han til at køle kviksølv ned til 4,2o K. Herved opdagede han at den elektriske modstand forsvandt. Dette åbnede mulighederne for, at kunne transportere ufattelige masser uden nogen gnidning. Det var dog først i 1933 at det lykkedes Meissner og Ochsenfeld, to tyske fysikere, at vise hvordan supralederens magnetfeltsvirkning kunne bruges som en kontaktanordning. Det store problem dengang var dog at man kun kunne bruge flydende Helium, som var meget dyr at fremstille, for at opnå de meget lave temperaturer. Derfor var det først i 1986 hvor forsøg med keramiske materialer fra en gruppe kaldet "perovskiter", foretaget af nogle schweiziske forskere, at man opdagede at disse allerede var supraledere ved 35o K. I 1987, efter at denne opdagelse var blevet videreudviklet, havde man fundet en perovskit, der allerede var supraledende ved 90o K. Egenskaberne ved perovskiter er at deres resistans vokser stykvis lineært med temperaturen. Fordi at man havde fået et materiale der var supraledende ved en så høj temperatur, gjorde at man kunne anvende flydende nitrogen, der opnås ved 77o K. Flydende nitrogen har en større køleevne end flydende Helium og er langt billigere at fremstille. I dag bruges også flydende nitrogen til køling af supraledende materialer og det er tilgængeligt ved mange universiteter og laboratorier der bruger det til at køle materialer ned med.Teknisk baggrundSupraledning er et af de fænomener, som man ikke ved alt om endnu. Det er ikke ligesom for eksempel tyngdekraften, hvor der er blevet opstillet utallige teorier og alle dens funktioner er blevet forklaret. Man har nemlig endnu ikke kunne forklare alle egenskaberne ved supraledning og man er stadig uenige omkring, hvilke teorier der er de korrekte. Et af de punkter hvor man er uenige, er om det er muligt at få supraledning ved stuetemperatur. Dette kommer af at den generelle teori om supraledning, siger at dette kun kan ske omkring det absolutte nulpunkt. Dog er det jo bevist, som vi tidligere har sagt, at man har opnået supraledning ved højere temperaturer, dette kaldes sjovt nok for "højtemperatur-supraledning".Superledere har den...

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