AQA A Level Physics

Revision Notes

5.2.3 Superconductivity

Superconductivity

  • All materials have some resistivity – even good electrical conductors such as copper and silver
  • Resistance means that when electricity flows through a material, it heats up and the electrical energy is wasted as thermal energy
    • The resistivity of a material can be lowered by lowering its temperature
  • If a material is cooled below a temperature called the critical temperature, its resistivity disappears entirely. It is now a superconductor
  • Therefore, a superconductor (or superconducting material) is defined as

A material with no resistance below a critical temperature

  • The critical temperature is defined as

The temperature at which a material becomes superconducting

  • A common superconducting material is mercury
    • Mercury has a critical temperature of 4.2 K
  • The temperature against electrical resistivity for a normal metal compared to a superconductor can be shown on the following graph:

Superconductivity Graph, downloadable AS & A Level Physics revision notes

Temperature against resistivity graph for a superconductor v a normal metal

  • Superconductivity is a property of only certain materials that have the characteristics above
  • This temperature threshold is sometimes referred to as the transition temperature

Exam Tip

Superconductivity occurs when there is no resistance. Avoid writing that there is a ‘little’ resistance or ‘thermal’ conductivity, which are not entirely correct

Applications of Superconductors

  • Superconductors are useful for applications that require large electric currents
  • Therefore, they are useful for:
    • The production of strong magnetic fields
    • The reduction of energy loss / dissipation in the transmission of electric power
  • Such applications which require these could be:
    • MRI scanners
    • Transformers & generators – for fewer fire risks
    • Motors
    • Monorail trains
    • Maglev (magnetic levitation) trains
    • Particle accelerators – need large magnetic fields to accelerate particles
    • Fusion reactors
    • Electromagnets
    • Power / electrical cables
    • Microchips
  • Maglev trains require extremely strong electromagnets to levitate the train due to such a large mass
    • This means they can travel at extremely high speeds up to 603 km / h
    • Maglev train systems currently only exist in Japan, South Korea and China

Maglev Train Diagram, downloadable AS & A Level Physics revision notes

Maglev trains use strong electromagnets attached to the train and rails to levitate

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