**Correct Option: 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: 1. **Basic Principle**: When a liquid is heated, it expands. This expansion causes the liquid to rise in a narrow glass tube. The amount the liquid rises corresponds to the temperature of the environment. 2. **Construction**: 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 uniformly with temperature changes. The scale on the thermometer is calibrated to correspond to specific temperature values. 3. **Reading the Temperature**: As the temperature increases, the liquid expands and moves up the tube. The height of the liquid column is then read against a calibrated scale, allowing the user to determine the temperature. 4. **Materials**: Mercury is often used because it has a high thermal conductivity, expands uniformly, and remains liquid over a wide range of temperatures. Alcohol is used in lower temperature ranges because it freezes at a lower temperature than mercury. ### 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 form a coil or strip. As the temperature changes, the differing expansion causes the coil to bend, which moves a pointer on a dial to indicate temperature. This method does not involve liquid expansion, making it different from 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, so it is not 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. ### Common Pitfalls - **Confusing Types**: Students often confuse different types of thermometers. It’s important to remember that liquid-in-glass thermometers specifically rely on liquid expansion, while others use different principles. - **Temperature Range**: Not all thermometers are suitable for all temperature ranges. For example, mercury thermometers are not used in very low temperatures due to freezing, while alcohol thermometers are not suitable for very high temperatures. - **Calibration**: Ensure that the thermometer is properly calibrated. Misreading the scale can lead to incorrect temperature readings. ### Revision Summary - A liquid-in-glass thermometer measures temperature through the expansion of a liquid (mercury or alcohol) in a glass tube. - The height of the liquid column corresponds to the temperature, which is read against a calibrated scale. - Other types of thermometers (bimetallic, thermocouple, infrared) operate on different principles and do not use liquid expansion. - Understanding the specific mechanisms of each thermometer type is crucial for accurate temperature measurement.