Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a particular temperature is called CRITICAL TEMPERATURE .
The electrical resistivity of most metals and many alloys drops suddenly to zero at very low temperature .This phenomena is called SUPERCONDUCTIVITY .
Superconductivity was discovered by Dutch physicist Heike Kamerlingh Onnes .
The critical temperature for mercury is 4.2 K . And the critical temperature for other superconducting elements varies from less than 0.1 K to nearly10 K .The elements which are good conductors such as copper and silver , do not become superconducting when cooled .
types of superconductors
There are many criteria by which superconductors are classified. The most common are:- Response to a magnetic field: A superconductor can be Type I, meaning it has a single critical field, above which all superconductivity is lost; or Type II, meaning it has two critical fields, between which it allows partial penetration of the magnetic field.
- By theory of operation: It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise.
- By critical temperature: A superconductor is generally considered high temperature if it reaches a superconducting state when cooled using liquid nitrogen – that is, at only Tc > 77 K) – or low temperature if more aggressive cooling techniques are required to reach its critical temperature.
- By material: Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium-titanium, germanium-niobium, and niobium nitride), organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon).
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