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, usually 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 This Answer is Correct**: - The key feature of the liquid-in-glass thermometer is its reliance on the thermal expansion of liquids. Both mercury and alcohol expand uniformly with temperature changes, making them suitable for accurate temperature measurement. - The design is simple and effective, allowing for a direct visual reading of temperature. 3. **Why the Other Options are Incorrect**: - **A. Bimetallic thermometer**: - This type of thermometer uses two different metals bonded together that expand at different rates when heated. The differential expansion causes the metal strip to bend, which moves a pointer on a dial. While it measures temperature, it does not use liquid expansion. - **B. Digital thermometer**: - Digital thermometers use electronic sensors (like thermocouples or thermistors) to measure temperature. They convert the temperature reading into a digital format for display. This method does not involve any liquid expansion. - **D. Infrared thermometer**: - Infrared thermometers measure the infrared radiation emitted by an object to determine its temperature. They do not use any liquid and are often used for non-contact temperature measurements. ### Formulas and Concepts - **Thermal Expansion**: The principle behind the liquid-in-glass thermometer is based on the formula for linear expansion: \[ \Delta L = L_0 \alpha \Delta T \] Where: - \(\Delta L\) = change in length (or volume for liquids) - \(L_0\) = original length (or volume) - \(\alpha\) = coefficient of linear (or volumetric) expansion - \(\Delta T\) = change in temperature ### Common Pitfalls - **Confusing Types of Thermometers**: Students often confuse different types of thermometers. It's important to remember that the liquid-in-glass thermometer specifically uses liquid expansion, while others use different principles. - **Misreading Scales**: When using a liquid-in-glass thermometer, ensure you read the scale at eye level to avoid parallax errors, which can lead to inaccurate readings. ### Revision Summary - The **liquid-in-glass thermometer** measures temperature through the expansion of liquids like mercury or alcohol. - It provides a direct visual reading based on the height of the liquid column in a glass tube. - Other types of thermometers (bimetallic, digital, infrared) use different principles and do not involve liquid expansion. - Understanding the working principle of each thermometer type is crucial for accurate temperature measurement.