Thermistor experiment

Today we put a thermistor into hot water with a thermometer and watched the resistance as the water cooled down. The resistance went up. I now understand the band theory idea better after learning some solid state quantum mechanics. Single atoms have clearly defined electron energy levels but as you bring atoms closer together to bond them, the electron energy levels cannot merge. Instead, for neighbouring atoms, one has its level nudge slightly up and the other has it nudge slightly down. On a grand scale, this results in a lot of almost but not quite identical electron energy levels. They form bands because they are grouped around the same energy. In semi-conductors, there is a clear gap between the valence band for bonding and the conduction band. Thermal energy is enough to move some electrons up from the valence band to the conduction band. More conduction electrons means higher current so we conclude that the resistance has fallen. The converse is true for cooling.