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 a step-by-step breakdown of how it works: 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, the molecules lose energy, and the liquid 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 is filled with a 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 easy reading. 4. **Common Uses**: - Liquid-in-glass thermometers are commonly used in laboratories, meteorology, and household applications due to their accuracy and reliability. ### Why Other Options Are Incorrect **A. Bimetallic thermometer**: - A bimetallic 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 type of thermometer, it does not use liquid expansion, which is the key characteristic of the liquid-in-glass thermometer. **B. Thermocouple**: - A thermocouple consists of two different metals joined at one end. When the junction is heated, it produces a voltage that can be correlated to temperature. This method relies on the thermoelectric effect rather than the expansion of a liquid, making it fundamentally different from a liquid-in-glass thermometer. **D. Infrared thermometer**: - An infrared thermometer measures temperature from a distance by detecting the infrared radiation emitted by an object. It does not involve any liquid or physical contact with the object being measured, which distinguishes it from the liquid-in-glass thermometer. ### Summary of Key Points - **Liquid-in-glass thermometers** measure temperature through the expansion of liquids (mercury or alcohol) in a glass tube. - They are marked with a scale for easy reading of temperature changes. - Other types of thermometers (bimetallic, thermocouple, infrared) operate on different principles and do not use liquid expansion. - Understanding the working principles of different thermometers is crucial for selecting the appropriate type 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.