The resistance in many electrical machines such as electric motors, generators and transformers is large, producing vast amounts of heat during its operation. These machines have to be large in size to dissipate the heat loss.
There are some metals and compounds whose resistances fall to zero below a certain critical temperature, Tc. When their resistances become zero, these materials are called superconductors.
Superconductivitiy was first discovered by H.K. Onnes in 1911 when he cooled mercury to below 4.2 K. Since then, many more superconductors have been found but all these materials still require cooling by expensive cooling agents such as liquid helium or liquid nitrogen making them impractical. The race is on for a room temperature superconductor.
Superconductors are very useful because they can make electric cars more feasible and computers much faster. Electrical energy can be stored in superconducting coils for future use and there will be no energy loss in superconducting electrical power lines. Another important and useful application is superconducting magnets which would make things like magnetic levitation (MAGLEV) trains and medical imaging machines such as the magnetic resonance imaging (MRI) scanner mode economical.