There are certain substances for which, when the temperature is decreased, the resistivity decreases and suddenly drops to zero at a certain temperature Tc that is called the critical temperature. Thereby giving rise to infinite conductivity, this phenomenon is known as superconductivity and the substance in this state is called a superconductor.
Application of Superconductivity:
1. To construct very strong magnets, to create a very high magnetic field at the cost of very low energy.
2. For transmission of electrical power through superconducting wires without any loss.
3. For the production of ultrafast computers.