In 1908, Heike Kamerlingh Onnes became the first scientist to produce liquid helium, achieving the lowest temperatures recorded up to that point. A number of researchers had suggested that materials behaved differently at very low temperatures, and this substance was important in allowing experiments that confirmed it. Working with solid mercury, Onnes demonstrated the phenomenon of superconductivity. This is when the electrical resistance of the metal drops suddenly to zero. No energy is lost as an electric current travels through the material, making it very efficient for storing or transmitting power. Since the work done by Onnes, other superconducting materials have been discovered that can be used at higher temperatures and which are therefore more economical.
 
There are a number of practical applications of superconducting materials. Many of these applications are based on the fact that the materials can be made into extremely powerful electromagnets. These are used in scientific experiments to direct beams of particles. They also form part of maglev trains – trains that float a small distance above the rails because of magnetic forces. Because there is no contact between the train and the rail this form of transport is capable of very high speeds, although it is unlikely to be in widespread use until costs drop considerably.

Superconductors are used in a variety of contexts. Very 6____________________ can be made out of superconducting materials and scientists use them in 7____________________. In transport, maglev trains rely on the 8____________________ produced in superconductors to raise the train above the rails, the lack of 9____________________ meaning that high velocities can be reached. The 10____________________ of maglev systems limit their use.