What is the principle of an electronic thermometer? Why does it need to be shaken after use to make the mercury column drop? An electronic thermometer is a kind of mercury thermometer. It is equipped with pure mercury in the glass bubble at the lower end and in the glass tube at the upper end, which is marked with temperature scales. Since the human body temperature does not exceed 42°C and does not fall below 35°C, the scales of the thermometer are from 35°C to 42°C, and each small grid represents 0.1°C. When testing the thermometer, the glass bubble at the lower end of the thermometer comes into contact with the human body because the body temperature is higher than that of the thermometer. The mercury in the glass bubble expands due to the heat from the body, rising along the glass tube until the mercury temperature matches the body temperature. The construction of the thermometer is very special. There is a very thin constriction at the junction of the glass bubble and the thin tube. When the thermometer is removed from the body, the mercury cools and contracts, and the mercury column breaks at the constriction. The upper mercury cannot return.So a thermometer can continue to display body temperature after it is removed from the body. Therefore, it needs to be shaken to make the mercury column fall. 2. Why is a thermometer triangular? When reading the temperature, the glass is colorless, and the mercury is gray and presents as silver white, but the mercury column is extremely thin and the color is difficult to observe, which causes difficulty in reading. To solve this problem, the upper part of the thermometer is made into a column with a triangular cross-section and a cylindrical surface. In this way, the side of the prism-shaped column can refract the light reflected from the mercury column at the interface between glass and air and amplify it, making it easier to read. 3.Electrical Sensing Device Conversion Principle: How does an electrical sensing device convert principles? Several typical sensors and their principles: Pressure sensor: Utilizes certain crystals, which generate a voltage when deformed in one direction, a phenomenon known as the piezoelectric effect, which converts force deformation into voltage. Alternatively, pressure-sensitive resistors, which change resistance when subjected to pressure, convert force into a change in electrical resistance, thereby generating corresponding electrical signals. Examples include sensors used in electronic scales. Light sensor: Utilizes so-called photoconductive devices, such as photocells (which can provide a certain current at the output end when illuminated), photoresistors, photodiodes, and transistors (which change internal resistance when illuminated) to convert light signals into electrical signals. Examples include sensors used in infrared alarm systems. Temperature sensor: Utilizes thermistors (which change resistance with temperature changes) or semiconductive materials in the form of PN junctions, whose conductivity changes at different temperatures, causing temperature transmitters. Examples include electronic thermometers, which use this type of sensor. However, semiconductor temperature sensors are not suitable for temperatures above 100 degrees. Industrial applications commonly use thermocouple sensors, which consist of two different metal wires or plates connected together to form a so-called "thermocouple." When the junction temperature rises, an electric potential (thermoelectric potential) is generated between the two metals. Measuring this potential allows the temperature at the junction to be determined, making thermocouples also a type of temperature sensor. Displacement sensor: When displacement causes a change in the position or medium between the electrodes of a capacitor; or when displacement causes a change in the position (coupling degree) of adjacent coils, the change in capacitance or the inductance or mutual inductance of the coils reflects the displacement. Vibration sensor: Of course, vibration can be detected using the piezoelectric effect, but it can also be achieved using electromagnetic induction, where vibration is transmitted to a coil, causing it to cut magnetic lines of force within a magnetic field, converting vibration into electrical signals (electromagnetic loudspeakers); or by transmitting vibration to the electrodes of a capacitor, causing the capacitance to change with the vibration, thereby generating electrical signals (polarized body microphones).Microphones used on mobile phones are all vibration sensors. Magnetic field sensors: Some materials exhibit a phenomenon where, when the magnetic flux passing through the material changes (i.e., the magnetic field strength changes), a voltage is generated perpendicular to the direction of the magnetic flux. This phenomenon is known as the Hall effect. By utilizing this effect, sensors that are sensitive to magnetic fields can be made. As for wind speed sensors and flow sensors, they essentially work based on the same principles mentioned above, and they are not listed individually.Why do you have to shake the thermometer before use? In simple terms, the thermometer has a triangular prism-shaped upper section with a thick glass layer. The middle is a thin tube, and the lower section is shorter and contains a filled mercury bubble. The upper and lower sections are directly connected by a very thin, curved channel. This design means that even after the thermometer is removed from the body, the reading will remain at its highest temperature (due to the vacuum formed in the very thin channel), and it will not decrease with the decrease in external temperature (it will only rise with temperature increases, the specific reason is explained in the references, and it is not convenient to elaborate here). In other words, without external force (using centrifugal force), the reading of the thermometer will rise and not decrease. Therefore, it is necessary to shake off the reading before each use to ensure accurate measurement.