噓 tengharold:stop posting crap. 12/13 16:43
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.
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 114.44.129.205