In superconductivity materials, its characteristics appear after it’s cooled below the critical temperature (varies between materials).This is mostly between 20Kelvin to 1K, e.g. solid mercury has critical temperature of 4.2K. Metals undergo metallic bonding where they have delocalised electrons allowing them to conduct in the form of heat and electricity. But, large amounts of energy are lost through heat, as the atoms collide with each other in the lattice structure. In a superconductor however, the electrons travel in pairs and move quickly between the atoms, so energy isn’t lost through heat making it more efficient. The Meissner effect is a defining characteristic of superconductivity, where it shows that the magnetic field is expelled when superconductivity is carried out.
http://www.howstuffworks.com/question610.htm
This table shows how the critical temperature varies between different superconductors.
Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes. He was studying the resistance of solid mercury at cryogenic (very low) temperatures, when at 4.2K; he observed that the resistance disappeared. More experiments were carried out further, and in 1913, lead was found to superconduct at 7K and niobium nitride at 16K in 1941. Superconductivity was further enhanced by the Meissner effect, the Ginzburg-Landua theory, the BCS theory and the Josephson Effect. The highest temperature superconductor is said to have a critical temperature of 138K!
Normal wires could be replaced by superconducting wires, so it’s more efficient as there’s no electrical resistance meaning no/less energy is lost. Superconducting magnets are some of the most powerful magnets known moreover. They are used in MRI and NMR machines, mass spectrometers, and in particle accelerators such as the ones in CERN. Nowadays, superconductors have been used to make digital circuits based on ‘rapid single flux quantum technology’ and RF/Microwave filters for mobile phone base stations. In the future, we could see superconductors used in high-performance smart grids, electric power transmission, transformers, power storage devices, electric motors, magnetic levitation devices, high-speed levitated trains and many more.
However, there’s no superconductors at room temperature, therefore we have to cool it a very low temperature for superconductivity to work. This is a MAJOR disadvantage, as it costs a lot of energy and money to get it to that temperature, making it less environmentally friendly as more fossil fuels are burnt adding to the effect of global warming/climate change.
For my practical, I’m measuring the resistivity of a metal and identifying it, linking it with this case study which is what it’s all about. So if the resistivity of that metal is zero; I know it’s a superconductor.
Bibliography
1. Physics Review
April 2004, Volume 13, Issue 4
‘Supercool’
Elizabeth Swinbank
2. AS Salters Horners Advanced Physics
Heinemann
Page 99
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