Superconductivity
When metals cool their resistance falls steadily as the motion of the atoms of the metal and the free electrons gets less. This means that there are fewer collisions between electrons and other electrons and between electrons and atoms.
However scientists discovered that as the metal was cooled further a temperature was reached where the resistance suddenly fell to zero.
When this happens the metal is said to be superconducting and the phenomenon is called superconductivity.
The temperature at which this happens for a certain metal is called the critical temperature for that metal. For pure metals the critical temperature is very low (usually below -270 oC) but recently scientists have made compounds that have relatively high critical temperature (as high as -70oC).
When a material is superconducting a current will flow through the material for hours without any external electromotive force being applied and without any energy being lost as heat.
Superconductors have tremendous benefits in electric motors and electrical circuits and superconducting electromagnets have been used in magnetic levitation (Maglev) trains and in some MRI scanners. The worldwide market for superconductor products is predicted to reach £25 billion by the year 2020.
Questions:
1. a) Why do materials have resistance?
b) What happens to the resistance of a metal as its temperature falls?
c) What happens as the temperature is reduced below the critical temperature?
2. What are metals called when they are below their critical temperature?
3. Why are superconducting motors so important?
4. Find out and write a sentence about the Japanese MLX01 test Maglev train.
5. Find out and write a sentence or two about the problems with the magnetic field that is produced when a current flows in a superconducting material.
A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS USB
