Liquid Thermometer
Liquid Thermometer
Liquid thermometers are based on the principle of change of volume of the liquid with change in temperature. These thermometers are suitable for a narrow range of measurements. The most commonly used liquids are (i) mercury and (ii) alcohol. The range of the mercury thermometer is - 39°C to 357°C. Alcohol thermometers are used only to measure temperature near ice points.
Mercury Thermometer
Mercury is usually selected for use in liquid in glass thermometers for the following reasons:
- It has a low specific heat and hence it absorbs little heat from the body whose temperature is being measured.
- It is a good conductor of heat and takes the temperature of the body quickly.
- It can be easily seen in a fine capillary tube and the thermometer can be made sensitive.
- It does not wet the wall of the glass tube. This is an important point for the construction of a thermometer.
- It has a uniform coefficient of expansion over a wide range of temperatures.
- It remains a liquid over a large range. Its freezing point is -39°C and its boiling point is 357°C.
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