A superconductor is a substance that conducts electricity without resistance when it becomes colder than a "critical temperature." At this temperature, electrons can move freely through the material. Superconductors are different from ordinary conductors, even very good ones. Ordinary conductors lose their resistance slowly as they get colder. In contrast, superconductors lose their resistance all at once. This is an example of a phase transition. High magnetic fields destroy superconductivity and restore the normal conducting state.
Normally, a magnet moving by a conductor produces currents in the conductor by electromagnetic induction. But a superconductor actually pushes out magnetic fields entirely by inducing surface currents. Instead of letting the magnetic field pass through, the superconductor acts like a magnet pointing the opposite way, which repels the real magnet. This is called the Meissner effect, and it can be demonstrated by levitating a superconductor over magnets or vice versa.
History of superconductors[change | change source]
|1911||superconductivity discovered by Heike Kamerlingh Onnes|
|1933||the Meissner effect discovered by Walter Meissner and Robert Ochsenfeld|
|1957||theoretical explanation for superconductivity put forward by John Bardeen, Leon Cooper, and John Schrieffer (BCS theory)|
|1962||the tunneling of superconducting Cooper pairs through insulating barrier predicted|
|1986||A ceramic superconductor was discovered by Alex Müller and Georg Bednorz. Ceramics are normally insulators. A lanthanum, barium, copper and oxygen compound with a critical temperature of 30K. Opened up the possibilities for new superconductors.|
Applications[change | change source]
- Superconducting quantum interference device (SQUID)
- Particle accelerators
- Small particle accelerators in health
- Levitating trains
- Nuclear fusion
- MRI Scanner