Superconductivity (AQA AS Physics) : Revision Note

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 electrical resistivity against temperature for a normal metal compared to a superconductor can be shown on the following graph:

Resistivity against Temperature graph for a superconductor vs. 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

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