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Temperature can be measured by using different types of thermometers and temperature scales. In addition, there are many methods being developed for measuring temperature. The devices which can be used to measure the temperature are: glass thermometer, thermocouples, thermistors, resistance temperature detector, pyrometers, and Langmuir probes etc. While measuring the temperature, one must be careful about the fact that the measuring instrument is reading the same temperature as that of the material. Sometimes, the heat from the measuring instrument can cause a temperature gradient. This will give rise to a wrong measured value of the temperature. Sometimes the windy conditions also lead to a wrong value measured by the instrument as well. Thus, the measurement of temperature of a material needs an extreme consciousness.
Thermal Expansion
Thermal expansion is the phenomenon in which the dimensions of a substance increase due to increase in temperature. When, there is a change in length by ΔL with a change in temperature ΔT, the phenomenon is called linear expansion (or contraction) and the coefficient of linear expansion is given by,
Here Li is the initial length of the substance. The value of α can be positive or negative. When α is positive, then there is linear expansion otherwise it is called linear contraction.
Similar to the linear expansion (or contraction) due to the change in temperature, the volume can also increase or decrease depending upon the increase or decrease of temperature. This phenomenon is called volume expansion. If the initial volume of a substance is Vi and the change in volume is ΔV due to the change in temperature ΔT then the coefficient of volume expansion is given by,
The coefficient of thermal expansion and the coefficient of volume expansion are related to each other as: β = 3α.
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Fluid Mechanics and Thermal Physics