“Are there materials whose resistance depends on the surrounding temperature?”
Wouldn’t be useful if we had a material whose resisted changed proportionally to temperature? For example, we could harness it for so many applications, such as in ventilation, we could increase the speed of a fan if the surrounding area becomes too hot, or maybe we could have a thermal conductivity measurement system. Well, thanks to the power of the human mind, there are in fact thermally sensitive resistors which are simply called thermresistors. Thermresistors come into two types, P-type and N-type. The resistance P-type thermresistor increase with temperature (P standing for positive), while the resistance of N-type (negative) thermresistors decrease with temperature. When using thermresistors, one has to be careful of the influence of thermal runaway effects that result from Joule heating. All in all, thermresistors are fascinating devices that are a testament the the raw power of human ingenuity.