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Tuesday, 30 July 2019

Applications of Superconductors

SUPERCONDUCTIVITY:


The resistance of material increases with increase in temperature. Similarly as the temperature is reduced its resistance also decreases. If the temperature is brought down to nearly -273°C, the resistance of some materials becomes zero. A state at which a material attains zero resistivity is called superconductivity. The temperature at which this transition takes place from normal conductivity to superconductivity is called transition temperature. Transition takes place almost suddenly and it has not been accounted for satisfactorily. It is found experimentally that if a current is induced in a mercury ring at a temperature of 4.5 degree Kelvin, it will continue to flow for years without taking any power from the source of supply. Similarly a lead ring carries a current of several hundred amperes over a year with no change.



Superconductivity has been observed to occur in poorer metallic conductors like tin, lead to rather than in better conductors like silver, copper etc. The biggest temperature at which superconductivity has been observed to occur is 20 degree Kelvin for a compound consisting of Niobium, Aluminium and Germanium. The transition temperature of some of the materials is given in Table.

Transition Temperature of Elements

Material
Transition temperature (oK)
Aluminium
1.14
Cadmium
0.6
Indium
3.77
Lead
7.26
Mercury
4.16
Tin
3.72
Uranium
0.8
Zinc
0.786
Pb 2 Au
7
Sn Sb
39
Copper Sulphide
1.6
Zinc Chloride
2.3

APPLICATIONS OF SUPERCONDUCTIVITY


On cooling a tin cylinder in a magnetic field and then measuring the field near its surface, it was found that the flux was suddenly affected as the cylinder became superconducting. It means as the metal became superconductor, the flux within it was thrust out. The magnetic field inside a metal in the superconducting state is zero regardless of its value before entering this state. The occurrence of unique magnetic state in a superconductor corresponding to B = 0 is of great importance because it means that the behaviour of a superconductor in a magnetic field is reversible.

FIELD APPLICATIONS OF SUPERCONDUCTORS IN PHYSICS


Superconductivity as it is does not find much application. This is on account of the difficulty involved in reaching a low temperature of -273°C and maintaining the equipment in that state but it is likely to find application in the following cases:

(a) Electrical Machines: The electrical generators and transformers can be easily manufactured by using superconductivity in exceptionally small size. These manufactured generators and transformers have efficiency nearly equal to 100%.

(b) Power Cables: A 200 kV cable with superconductivity material will enable transmission of power over long distances using thin conductors without any significant power loss and voltage drop.

(c) Electromagnets: Superconducting solenoids have been made in such a way that it do not produce any heat during operation. It acts as a substance with zero magnetic permeability. Therefore the external magnetic field in the superconductor repels each other. The property can be utilized in developing frictionless bearings with magnetic lubrication. These frictionless bearings are most common in gyroscopes and electrical machines.

APPLICATIONS OF SUPERCONDUCTORS IN CHEMISTRY


Helium, an expensive gas is now used to attain low temperatures, required for superconductivity. Efforts are being made to develop compound which are superconductors at temperatures possible to obtain by easily available hydrogen gas.



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