Superconductors are materials which have zero resistivity at and below a critical temperature. This temperature differs for each material, but currently are too low to be usefully used. If materials with high enough critical temperatures can be developed, they could be used in electricity transmission to reduce energy loss as well as in the production of strong magnetic fields. Semiconductors are components for which the resistance changes depending on external conditions. The two main types you need to know about are: 1. Light Dependant Resistors are light sensitive components - when light intensity increases, their resistance decreases 2. Thermistors are temperature sensitive components - when the temperature increases, their resistance decreases