Types of thermometers: 1. Liquid crystal thermometer: Liquid crystals made with different formulas have different phase transition temperatures. When they undergo phase transition, their optical properties also change, making the liquid crystal appear colorless. If liquid crystals with different phase transition temperatures are coated on a piece of paper, the temperature can be determined by the color change of the liquid crystals. The advantage of this thermometer is that it is easy to read, but the disadvantage is its insufficient temperature. It is commonly used in ornamental fish tanks to indicate water temperature. 2、 Resistance thermometer: The resistance of metal increases with temperature, and in the case of little temperature change, its resistance is approximately linearly related to temperature. In a larger temperature range, it can usually be represented by a simple quadratic polynomial. By measuring the resistance of a metal, the temperature can be determined. This type of thermometer is usually made of white gold wire and can reach 10-3 degrees, commonly used for precise measurements. Due to the high melting point of platinum, the temperature range that can be measured is larger, around -250 degrees Celsius to 1200 degrees Celsius. 3、 Gas thermometer: A gas with low density under fixed pressure, whose volume is linearly related to temperature. A thermometer made using this relationship is called a constant pressure gas thermometer. A gas with a fixed volume and low density has a linear relationship between pressure and temperature. A thermometer made using this relationship is called a constant volume gas thermometer. 4、 Rotary thermometer: A rotary thermometer is made of a coiled bimetallic strip. One end of the bimetallic strip is fixed, and the other end is connected to a pointer. Due to different degrees of expansion, the two metal sheets curl differently at different temperatures, causing the pointer to point to different positions on the dial. The temperature can be determined from the reading on the dial. 5、 Semiconductor thermometer: The resistance change of semiconductors is different from that of metals. When the temperature increases, their resistance actually decreases, and the magnitude of the change is relatively large. Therefore, even a small temperature change can cause a significant change in resistance, resulting in thermometers with high precision and often referred to as temperature sensors. 6、 Thermocouple thermometer: A thermocouple thermometer is composed of two different metals connected to a sensitive voltmeter. Metal contacts will generate different potential differences at the two ends of the metal at different temperatures. The potential difference is very small, so a sensitive voltmeter is needed to measure it. The temperature can be determined from the reading of the voltmeter. 7、 Optical thermometer: When the temperature of an object is high enough to emit a large amount of visible light, the amount of its thermal radiation can be measured to determine its temperature. This type of thermometer is called an optical thermometer. This thermometer is mainly made up of a telescope equipped with a red filter and a set of circuits with small light bulbs, ammeters, and variable resistors. Before use, establish the relationship between the temperature corresponding to different brightness levels of the filament and the reading on the ammeter. When in use, align the telescope with the object being measured, adjust the resistance to make the brightness of the light bulb the same as that of the object being measured. At this point, the temperature of the object being measured can be read from the ammeter.