Superconductivity Electricity is best defined as the flow of electrons in a conductor. Superconductivity is a phenomenon in which certain metals, alloys, and ceramics conduct electricity without resistance. Superconductivity occurs in metals and alloys such as lead, mercury, and tin, at temperatures near absolute zero. In 1911, Heike Kamerlingh Onnes discovered superconductivity while researching the effects of extremely cold temperatures on different metals. Onnes discovered that

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Superconductivity


Electricity is best defined as the flow of electrons in a conductor. Superconductivity is a
phenomenon in which certain metals, alloys, and ceramics conduct electricity without
resistance. Superconductivity occurs in metals and alloys su
ch as lead, mercury, and tin,
at temperatures near absolute zero.

In 1911, Heike Kamerlingh Onnes discovered superconductivity while researching the
effects of extremely cold temperatures on different metals. Onnes discovered that
mercury lost all resista
nce to the flow of electricity when cooled to about 4K.

Before Onnes’ discovery, there wasn’t any way to eliminate resistance. Although copper,
aluminum, silver, and gold are excellent conductors, there is a loss of some electrical
energy because of resist
ance.

The modern theory of superconductivity, the BCS theory (named for the developers of
the theory, Bardeen, Cooper, and Schrieffer), says that a superconductor has no electrical
resistance because of an attractive interaction between its electrons tha
results in the
formation of pairs of electrons. These pairs of electrons are bound to one another and
flow without resistance around impurities and other imperfections. In an ordinary
conductor, resistance occurs because its unbound electrons collide with
imperfections an
then scatter.

Superconductivity is use in the field of electromagnetics. Powerful superconducting
magnets use less electricity than ordinary magnets. These magnets are being used in
many areas including medicine, transportation, and the s
tudy of physics.

In the medical field, magnetic resonance imaging (MRI) machines use a superconducting
magnet to generate a powerful magnetic field. MRI technology allows physicians to
identify abnormalities without performing surgery and without exposing
the patient to
radiation.

Magnetically Levitated Trains, called Maglev trains, use superconducting
electromagnetic coils. The coils are mounted on the bottom of the train an aluminum
coils or sheets are set in the guideway. When the train moves over the g
uideway, it
induces a current. The guideway coils become electromagnets with the same polarity as
the train coils. The two types of coils then repel each other. The repulsion force is strong
enough to raise the train.


http://www.howstuffworks.com/maglev
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train.htm