How Does a Thermometer Measure Temperature
- Mercury Thermometer
The upper part of a mercury thermometer consists of a glass tube, with a glass bulb at the lower end. Pure mercury is contained in the bulb and the lower end of the tube, and a scale is marked on the tube. Since the human body’s maximum temperature does not exceed 42°C and the minimum temperature is not below 35°C, the thermometer’s scale ranges from 35°C to 42°C, with each division representing 0.1°C.
To read, grasp the end of the thermometer (away from the mercury column), align the eye line with the upper surface of the liquid column, hold it horizontally, and slowly rotate the thermometer. While rotating, observe the thermometer until a thick mercury column is visible from the front, indicating the corresponding temperature. Typically, look at the edge between the scale and the number, with the scale facing up, the triangle edge facing you, and a white mercury line visible. The corresponding number position indicates the body temperature.
- Electronic Thermometer
The body temperature of an electronic thermometer is displayed on the screen. After measurement completion, remove it upon hearing the prompt tone, and the thermometer’s screen displays the temperature index.
- Infrared Ear Thermometer
Similar to an electronic thermometer, the infrared ear thermometer displays the temperature index on the screen after completing the measurement. Remove the thermometer to check the screen temperature index.
Principle of a Mercury Thermometer
When using a mercury thermometer, the glass bulb at the bottom contacts the human body. Due to the body’s higher temperature, the mercury in the bulb expands, rises along the thin glass tube, and stops when its temperature matches the body’s temperature.
The mercury thermometer features a thin constriction where the glass bulb meets the thin tube. As the thermometer leaves the body, the mercury cools, contracts, and disconnects at the constriction. The mercury above cannot return, allowing the thermometer to continue displaying the body temperature after leaving the body.
Post-use, the thermometer should be “returned to the watch,” meaning it is shaken down hard, allowing the risen mercury to return to the vacuole. Other thermometers should not be shaken, highlighting a significant difference between mercury thermometers and other liquid thermometers.
Advantages and Disadvantages of Mercury Thermometers
- Advantages
Mercury thermometers retain a high mercury column with body temperature rise, allowing convenient observation. With a compact glass structure and stable mercury performance, these thermometers provide accurate indication and high stability. They are also cost-effective, require no external power supply, and are trusted, especially in medical settings.
- Disadvantages
Mercury thermometers have evident drawbacks, including fragility, potential mercury pollution upon breakage, and the need for mercury disposal. They are less convenient due to longer measurement times and the absence of direct body temperature display like electronic thermometers.