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Temperature

thermometers


When we assume that the linear expansion ΔL of a metal bar of length L is proportional to the change in temperature ΔT, according to

ΔL = α L ΔT


then we only need to set a temperature scale in order to have a thermometer.
Celsius selected 0oC when the metal bar was placed in melting ice and 100oC when the bar was placed in boiling water.
For the linear thermal expansion coefficient α Celsius obtained then

L(T=100oC) - L(T=0oC) = ΔL = α L ΔT = α L (100-0) = 100α L


Tables of linear thermal expansion coefficients can be found in many places, like in WikipediA, or in the Engineering ToolBox.
Kelvin used the absolute zero temperature of -273.15oC to define 0 K. But the Kelvin unit of 1 K is equal to the Celsius unit of 1oC. As a consequence linear thermal expansion coefficients are exactly the same in Kelvin units as in Celsius units.

Several types of thermometers and thermal controllers make use of bimetallic strips. A bimetal bends under temperature changes which allows for temperature to be measured.
Other types of thermometers make use of a liquid column.

Thermal expansion is sometimes the cause of railroad accidents. Heat expands the rail and when there are no joints to create any extra room, then thermal expansion creates pressure on the steel. When the pressure becomes too much, the track can buckle or bulge out considerably, giving rise to so-called sun kinks.


volumetric expansion