The correct option is **C. Liquid-in-glass thermometer**. ### Detailed Explanation 1. **Understanding the Liquid-in-Glass Thermometer**: - A liquid-in-glass thermometer consists of a glass tube that contains a liquid, typically mercury or colored alcohol. - As the temperature increases, the liquid expands and rises in the tube. Conversely, when the temperature decreases, the liquid contracts and falls back down the tube. - The height of the liquid column corresponds to the temperature, which can be read against a calibrated scale marked on the glass. 2. **Why Option C is Correct**: - The defining feature of a liquid-in-glass thermometer is its reliance on the thermal expansion of a liquid. This principle is based on the fact that most liquids expand when heated and contract when cooled. - Mercury is often used because it has a high thermal conductivity, a wide temperature range, and does not wet the glass, allowing for a clear reading. Alcohol is used in lower temperature ranges because it remains liquid at lower temperatures. 3. **Why the 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. This method does not involve liquid expansion, making it different from the liquid-in-glass thermometer. - **B. Infrared thermometer**: - An infrared thermometer measures temperature by detecting the infrared radiation emitted by an object. It does not use any liquid or physical contact with the object being measured. This method is based on the principles of thermography and is used for non-contact temperature measurements. - **D. 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. ### Formulas and Calculations While there are no specific formulas for reading a liquid-in-glass thermometer, understanding the concept of thermal expansion is important. The linear expansion of a liquid can be described by the formula: \[ \Delta L = \alpha L_0 \Delta T \] Where: - \(\Delta L\) = change in length (or height of the liquid column) - \(\alpha\) = coefficient of linear expansion of the liquid - \(L_0\) = original length (or height of the liquid column) - \(\Delta T\) = change in temperature ### Common Pitfalls - **Reading Errors**: Ensure that you read the thermometer at eye level to avoid parallax errors. - **Temperature Range**: Be aware of the temperature range of the liquid used; for example, mercury thermometers are not suitable for very low temperatures as mercury freezes. - **Calibration**: Always check that the thermometer is calibrated correctly before use. ### Revision Summary - The **liquid-in-glass thermometer** measures temperature through the expansion of a liquid (mercury or alcohol). - **Bimetallic thermometers** use metal expansion, **infrared thermometers** measure radiation, and **thermocouples** rely on voltage generation. - Understanding the principles of thermal expansion is key to grasping how liquid-in-glass thermometers work. - Always ensure proper reading techniques and awareness of the thermometer's limitations for accurate measurements.