Resistance and humidity
The resistance of the conductor is related to temperature. The resistance of pure metal increases with the increase of temperature, and the temperature rises by 1 °C and the resistance value increases by a few thousandths. The resistance of carbon and insulator decreases with increasing resistance. The relationship between the semiconductor resistance value and the temperature is large, and the temperature is slightly increased, and the resistance value is greatly reduced. The resistance of some alloys such as constantan and manganese copper has little to do with temperature changes. These conditions of resistance change with temperature are useful. A resistance thermometer can be fabricated using the relationship between resistance and temperature change. The platinum resistance thermometer can measure temperatures from 263 ° C to 1000 ° C. The semiconductor 锗 thermometer can measure very low temperatures. Constantan and manganese copper are good materials for making standard resistors.
For example, the filament of a light bulb is made of tungsten wire, and the resistance of the filament when it is normally illuminated is much larger than the resistance at normal temperature?
The resistance of tungsten increases with increasing temperature, and the temperature increases by 1 °C and the resistance increases by about five thousandths. When the filament emits light, the temperature is about 2000 ° C, so the resistance value is increased by about 10 times. When the filament is illuminated, the resistance is much larger than when it is not illuminated. When the circuit is turned on, the filament resistance is very small, and the electrical equipment is easily damaged at this moment.