Thermometer

Thermometer is a device used to measure temperature of a body. There are many types of thermometers

based on different working principles and have limitation of measuring temperature also. For example liquid thermometer can’t measure the temperature below freezing point and above boiling point of liquid. Generally mercury thermometer and alcohol thermometer are liquid thermometers. Liquid thermometers are based upon the principle of expansion of liquid with temperature. As shown in figure, in mercury thermometer mercury is enclosed inside conducting metal bulb. The bulb is connected to narrow transparent capillary tube. The tube is covered with glass jacket from outside for protection. Zero degree Celsius is determined by placing the bulb in melting ice which called lower fix point and 100 degree Celsius is determined by placing the thermometer bulb on steam of boiling water which is called upper fix point. The distance between two fix points are divided to 100 equal parts and each part indicates 1 degree Celsius.
An alcohol thermometer is same almostly only the difference that liquid is colored alcohol instead of mercury. As alcohol has low freezing points it is popularly used by mountaineers to measure surrounding temperature during mountain climbing. Instead of liquid thermometer there are many other types of thermometers such as

• Constant pressure gas thermometers
• Constant volume thermometers
• Platinum resistance thermometers
• Thermocouple thermometers
• Pyrometer Thermometers
• Pacifier thermometers
• Plastic strip thermometer

Q. Why water can’t be used as thermometer liquid?

Answer: Water can’t be used as thermometer liquid because it has irregular expansivity (anomalous expansion), Low range of freezing and boiling points, adhere on glass tube etc.