4. Thermometer and its types

Thermometer

• Mercury and alcohol both remain in a liquid state even when the temperature changes.
• Both have a high coefficient of expansion, which helps measure the small changes in temperature by measuring the expansion in the volume of the liquid.

• It has a uniform expansion (For equal amounts of heat, mercury expands by equal lengths).
• It is opaque (non-transparent) and shining.
• It does not attach to the sides of the glass tube.
• It is the only element in the liquid state at room temperature.
• It is a good conductor of heat (but comparatively low compared to other metals).
• The range of temperatures measured using a mercury thermometer is high because mercury has a high boiling point of \(357\)\(°C\) and a freezing point of \(−\)\(39\)\(°C\).

Properties of alcohol:

• The freezing point of alcohol is less than \(−\)\(100\)\(°C\). So we can use it to measure very low temperatures.
• Its expansion per degree Celsius increase in temperature is very large.
• It can be coloured brightly and hence it is easily visible.

• Clinical thermometer

• Laboratory thermometer

• Digital thermometer

• Infrared thermometer