FREE ESSAY ON CONDUCTORS

CONDUCTORS

Super conductivity is a natural phenomenon in which certain materials such as metals,
alloys, and ceramics, can conduct electricity without resistance. These materials are
what we call superconductors. In a superconductor, once the flow of electrons begins, it
essentially goes on forever, making it an important material to humans. 
Superconductivity was discovered by a Dutch scientist by the name of Heike Kamerlingh
Onnes in 1911. While researching properties of materials at absolute zero, this man found
out that certain materials lost its resistance to the flow of electrons. For years to
come, his discovery was at the head of theoretical interest. The only problem though, was
that people at that time could not even think of a way to produce such a temperature, to
allow materials to be superconductors at all times. This all changed in 1986 when Karl
Muller and George Bednorz were working at the IBM Research Division in Zurich,
Switzerland. They found a material that reached superconductivity at around 35 degrees
Kelvin or -238 degrees Celsius. In the next year, a team of Chinese-American physicists
declared that they had found a material that reached superconductivity at 92 degrees
Kelvin. This was a big improvement. 92 degrees Kelvin is not a very high temperature, in
fact, it is the equivalent of -181 degrees Celsius. Locating superconducting material
above 77 degree Kelvin is a good thing because it means that the material will be easily
produced and used. A theoretical understanding of superconductivity was advanced in 1957
by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of
Superconductivity became know as the BCS theory (which came from each mans last name) and
won them a Nobel prize in 1972. The BCS theory explained superconductivity at
temperatures close to absolute zero. However, at higher temperatures and with different
superconductor systems, the BCS theory has consequently became insufficient to fully
explain electron behavior.
The Type 1 category of superconductors is basically made up of pure metals that normally
show conductivity at room temperature. They require really cold temperatures to slow down
molecular vibrations enough to facilitate unrestrained electron flow in agreement to the
BCS theory. BCS theory suggests that electrons team up in cooper pairs in order to help
each other overcome molecular obstacles. Type 1 superconductors were discovered first and
require the coldest temperatures to become superconductive. They are characterized by a
very sharp transition to a superconducting state. Ironically, copper, silver and gold,
three of the best metallic conductors, do not rank among the superconductive elements. 
Except for the elements vanadium and niobium, Type 2 superconductors consists of metallic
compounds and alloys. The recently discovered superconducting perovskites or
superconducting ceramics belong to this Type 2 group. Type 2 superconductors differ from
Type 1 in that their transition from a normal to a superconducting state is regular
across a region of mixed behavior. A Type 2 superconductor will also allow some invasion
by an outer magnetic field into its surface. A Type 1 superconductor won't. 
Super conductors have many uses. They are used in trains as magnetic-levitation devices,
which makes certain trains appear to float while in motion. Superconductors are also used
medically in MRI's and commonly in electric generators, making them more efficient.