Thursday 23 July 2015

Superconductivity

SUPERCONDUCTIVITY

In case of a conductor when the temperature increases then its electrical resistance also increases because it has positive temperature coefficient of resistance. It means if we decrease the temperature then the electrical resistance of conductor will also decrease. In some materials when we go on decreasing the temperature then at a particular temperature known as critical temperature the electrical resistance of conductor becomes zero. Thus conductor becomes superconductor. This phenomenon is called superconductivity. Critical temperature for mercury is 4.2K , Lead 7.2K and Tl-Ba-Cu-oxide 125K.
It means the electrical resistance of mercury becomes zero at 4.2K temperature.

One  of  the  truly  remarkable  features  of  superconductors  is  that  once  a  current  is set  up  in  them,  it  persists  without  any  applied  potential  difference (because  R " 0).  Steady currents  have  been  observed  to  persist  in  superconducting  loops  for  several  years  with no apparent decay! An  important  and  useful  application  of  superconductivity  is  in  the  development  of superconducting  magnets,  in  which  the  magnitudes  of  the  magnetic  field  are  about ten  times  greater  than  those  produced  by  the  best  normal  electromagnets.  Such superconducting  magnets  are  being  considered  as  a  means  of  storing  energy.

Superconducting  magnets  are  currently  used  in  medical  magnetic  resonance  imaging (MRI)  units,  which  produce  high-quality  images  of  internal  organs  without  the  need for excessive exposure of patients to x-rays or other harmful radiation.

Applications

(i) Superconductors form the basis of energy saving power systems, namely the superconducting generators, which are smaller in size and weight, in comparison with conventional generators.
(ii) Superconducting magnets have been used to levitate trains above its rails. They can be driven at high speed with minimal expenditure of energy.
(iii) Superconducting magnetic propulsion systems may be used to launch satellites into orbits directly from the earth without the use of rockets.
(iv) High efficiency ore–separating machines may be built using superconducting magnets which can be used to separate tumor cells from healthy cells by high gradient magnetic separation method.
(v) Since the current in a superconducting wire can flow without any change in magnitude, it can be used for transmission lines.
(vi) Superconductors can be used as memory or storage elements in computers.


For detailed study visit:-
http://www.extremetech.com/extreme/208651-what-is-superconductivity

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