The correct option is **C. Liquid-in-glass thermometer**. ### Explanation of the Correct Answer A liquid-in-glass thermometer is a device that measures temperature by utilizing the principle of thermal expansion of a liquid, typically mercury or colored alcohol. Here’s how it works step-by-step: 1. **Basic Principle of Thermal Expansion**: When a liquid is heated, its molecules gain energy and move faster, causing the liquid to expand. Conversely, when the liquid cools, it contracts. This property is fundamental to the operation of a liquid-in-glass thermometer. 2. **Construction of the Thermometer**: A liquid-in-glass thermometer consists of a glass tube that is sealed at one end. The tube contains a small amount of liquid (mercury or alcohol) that expands and contracts with temperature changes. The other end of the tube is open to the atmosphere, allowing the liquid to move freely. 3. **Reading the Temperature**: The glass tube is marked with a scale (usually in degrees Celsius or Fahrenheit). As the temperature increases, the liquid expands and rises in the tube. The height of the liquid column corresponds to a specific temperature on the scale, allowing for an accurate reading. 4. **Common Uses**: Liquid-in-glass thermometers are widely used in laboratories, meteorology, and various industrial applications due to their accuracy and reliability. ### Why the Other Options Are Incorrect - **A. Bimetallic thermometer**: This type of thermometer uses two different metals that expand at different rates when heated. These metals are bonded together, and as they expand, they bend, moving a pointer on a dial to indicate temperature. While it is a valid temperature measurement device, it does not use liquid expansion, which is the key characteristic of the liquid-in-glass thermometer. - **B. Digital thermometer**: Digital thermometers use electronic sensors to measure temperature and display the reading on a digital screen. They do not rely on the physical expansion of a liquid, making them fundamentally different from liquid-in-glass thermometers. - **D. Infrared thermometer**: Infrared thermometers measure temperature from a distance by detecting the infrared radiation emitted by an object. They do not involve any liquid or physical expansion, which again sets them apart from liquid-in-glass thermometers. ### Summary of Key Points - **Liquid-in-glass thermometers** measure temperature through the expansion of liquids (mercury or alcohol) in a glass tube. - They are accurate and widely used in various fields due to their reliable performance. - Other types of thermometers (bimetallic, digital, infrared) operate on different principles and do not utilize liquid expansion. - Understanding the working principles of different thermometers is crucial for selecting the appropriate device for specific applications. This thorough understanding of the liquid-in-glass thermometer and its comparison with other types will help you grasp the fundamental concepts of temperature measurement in physics.