http://nobelprize.org/nobel_prizes/physics/laureates/2003/public.html An unexpected cold effect When investigations were first carried out into the nature of electricity in the 19th century, it was evident that metals and certain alloys conduct electricity by allowing electrons to move between the atoms. But the disorganized way in which the electrons move causes the atoms to vibrate, so heat is generated. If the current is too strong, the heat can be so great that the conductor melts. In addition it was found that an electric current through a conductor creates a magnetic field, which in turn generates current in the opposite direction. Electricity and magnetism interact and can thus counteract each other. In 1911 the Dutch physicist Heike Kamerlingh Onnes made a remarkable discovery. He was particularly interested in the properties of substances at low temperatures and had succeeded in producing liquid helium, which has an extremely low temperature. When Onnes investigated the electric conductivity of mercury, he found that when the metal was cooled by means of liquid helium to a few degrees above absolute zero, its electric resistance vanished. He named this phenomenon superconductivity. Although no theoretical explanation could be found for this phenomenon, it was evident that it could have far-reaching significance in a modern society that was becoming more and more dependent on electricity. --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 114.44.129.205