Analysis:

mercury thermometer

(Glass thermometer)

This is a traditional thermometer, which can be placed under the tongue or under the armpit. Children should be careful when using it, because it is easy to break. Mercury must be "shaken" back to 35 degrees Celsius before use. The temperature measuring time is about 3 minutes. Be sure to disinfect and clean after use.

Ear electronic thermometer

(Ear thermometer)

You must put on a disposable transparent plastic sleeve. Put the thermometer directly in the ear, and infrared rays can measure the temperature in three or two seconds, which is suitable for babies and children. Generally, the measured body temperature is higher than that of electronic oral thermometer and glass mercury thermometer.

Temperature detection strip

(fever thermometer)

A plastic sticker on the forehead is filled with crystal liquid, which represents the colors of different temperatures according to the change of body temperature. The accuracy of temperature measurement is low, because it is not the same as the skin temperature. For example, in an air-conditioned room, the skin temperature is slightly cold, so the measured body temperature is often lower than the actual one. The temperature measurement takes about 15 seconds.

Electronic oral thermometer

(Oral digital thermometer)

You can put it under your tongue or armpit for about a minute or two. When the temperature to be measured is stable, the thermometer will beep. Pay attention to whether the battery works normally, otherwise the temperature measurement is not allowed.

Types of thermometers

(1) liquid crystal thermometer: Liquid crystals made of different formulations have different phase transition temperatures. When they undergo phase transition, their optical properties will also change, making the liquid crystals look discolored. If liquid crystals with different phase transition temperatures are coated on a piece of paper, the temperature can be known from the change of liquid crystal color. The advantage of this thermometer is that it is easy to read, but the disadvantage is that it is not accurate enough. Often used to watch fish tanks, indicating water temperature.

(2) Resistance thermometer: The resistance of metal will increase with the increase of temperature. Under the condition of little temperature change, its resistance is linear with temperature. In a large temperature range, it can usually be expressed by a simple quadratic polynomial. By measuring the resistance of metal, we can know what the temperature is. This kind of thermometer is usually made of platinum wire, which can be accurate to 10-3 degrees Celsius, and is often used for precise measurement. Because of the high melting point of platinum, the measurable temperature range is large, about -250℃ to 1200℃.

(3) Gas thermometer: Under a certain pressure, the volume of gas with low density has a linear relationship with temperature. A thermometer made of this relationship is called a constant pressure gas thermometer. In a certain volume, the pressure and temperature of low-density gas are linear. A thermometer made from this relationship is called a constant volume gas thermometer.

(4) Rotating thermometer: The rotating thermometer is made of curled bimetal. One end of the bimetal is fixed and the other end is connected with the pointer. The expansion degree and temperature of the two metal sheets are different, which leads to the different curling degree of the bimetal. Then the pointer points to different positions on the dial, and its temperature can be known from the readings on the dial.

(5) Semiconductor thermometer: The resistance change of semiconductor is different from that of metal. With the increase of temperature, its resistance decreases and changes greatly. Therefore, a small amount of temperature change can also make the resistance change obviously. The thermometer has high precision and is often called a temperature sensor.

(6) Thermocouple thermometer: Thermocouple thermometer consists of two different metals connected to a sensitive voltmeter. Metal contacts will produce different potential differences at both ends of the metal at different temperatures. The potential difference is so small that a sensitive voltmeter is needed to measure it. We can know what the temperature is from the reading of the voltmeter.

(7) Optical pyrometer: If the temperature of an object is high enough to emit a large amount of visible light, the temperature can be determined by measuring the amount of its thermal radiation. This kind of thermometer is an optical thermometer. This thermometer mainly consists of a telescope with a red filter and a set of circuits with a small bulb, an ammeter and a variable resistor. Before use, establish the relationship between the temperature corresponding to different brightness of filament and the reading on ammeter. When in use, aim the telescope at the measured object, and adjust the resistance so that the brightness of the bulb is the same as that of the measured object. At this time, the temperature of the object to be measured can be read from the galvanometer.