Thermometer

Topics: Temperature, Liquid, Thermodynamics Pages: 2 (362 words) Published: June 8, 2013
 
Thermometer is the device used to measure temperature.
The extremely fine tube (narrow bore) of a thermometer is called a capillary. The boiling point of water (or condensing point of steam) is 100oC or 212oF or 373 K. The freezing point of water (or melting point of ice) is 0oC or 32oF or 273 K. These temperatures are typically used in the calibration of thermometers and are known as the fixed points. The temperature range that is typically marked on a laboratory thermometer is −10oC to 110oC.  

Thermometric liquids are those that are used in thermometers. Some examples of such liquids are mercury and alcohol.
The thermometric fluid used by Galileo Galilei in his thermometer was air.  
Alcohol, which is used as a thermometric liquid, has the following characteristic properties : 1. Alcohol has a very low freezing point of about −112oC and hence is suitable in thermometers to record very low temperatures. 2. Alcohol has a low boiling point of about 78oC and therefore cannot be used to measure high temperatures. 3. Alcohol can be colored brightly (by adding a dye, generally red) and then it is clearly visible through glass. 4. Alcohol expands more than mercury.

5. Alcohol is fairly inexpensive.
6. Alcohol wets glass.
7. Alcohol is not a good conductor of heat.
 
Mercury, which is used as a thermometric liquid, has the following characteristic properties : 1. Mercury has a high boiling point of about 357oC and therefore can be used to measure temperatures as high as 357oC. 2. Mercury has a freezing point of about −39oC and hence is suitable in thermometers to record low temperatures (although not very low temperatures). 3. Mercury is opaque and has a shining silvery color of its own, making it clearly visible in the capillary tube of a thermometer. 4. Mercury needs very little heat to expand and so it can easily measure the temperature of a body without causing a decrease in the body's temperature. 5. Mercury does not stick to the side of the glass...
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