Question

How does thermal expansion affect a thermometer?

Answer 1

Hint: The basic working principle of a thermometer is thermal expansion. When the thermometric matter gets the heat energy then it expands and this expansion shows the increased temperature reading on the calibrated scale.

Complete step by step answer:
• Thermal expansion is the basis of which a thermometer works. This is due to the thermodynamic properties “a substance expanding and retracting due to changes in heat”.
• Generally, material expands when receives heat and contracts at lower temperatures
• In the case of a thermometer, there is a thin glass tube with a colorful liquid in it (that rises up with a certain measurement on the thermometer). The tube is made thin to get a more precise reading. The tube is so thin that the liquid can either move up or down. And this is where thermal expansion comes in as the liquid will rise or fall (generally rise for increased temperature) when the liquid expands or contracts according to temperature.
• When a liquid receives energy in the form of heat, the atoms of the liquid will gain energy and will get "excited", due to this energy they move further apart i.e., they have expanded. The tube is so thin that they have nowhere to go but up. Thus, they will mark the increase in temperature for the thermometer.
• The reverse is for cooling. At lower temperatures the atoms come closer and take up a smaller area, so as the liquid contracts the level goes down and goes down in the thermometer, indicating a decrease in temperature.
• The expansion rate depends upon various factors like specific heat and coefficients of linear expansion. Higher the coefficient of linear expansion, the more accurate the reading because it gives the highest change in length for a certain change in temperature.

Note:
• Thermal expansion is the internal property of the material
• Thermal expansion of a body is denoted by $\alpha$, whenever a body receives heat it tends to expand
• Covalent materials such as diamond, silicon carbide and silicon nitride have strong bonds between atoms, resulting in low coefficients of thermal expansion