meaning of thermal expansion, explanation of thermal expansion in solids ( linear, superficial and volumetric) and liquids
Answers
Thermal expansion can be defined as the change in the length, width, height, or volume of any material on changing the temperature. Thermal expansion is very evident in solids as atoms are densely packed.
Thermal Expansion in Metals:
- It is a well-known phenomenon now that substances expand on heating and contract on cooling.
- If you heat a body, it alters its dimensions.
- Depending on the shape of the body.
- The expansion can occur in length in which case it is called Linear Expansion.
- If we take a square tile and heat it, the expansion will be on two fronts, length and breadth, here it is called Area Expansion.
- If we take a cube and heat it, all its sides expand and now the body experiences an increase in the overall volume due to this and it is called Volume Expansion.
Linear Expansion:
Δl/l=αl.ΔT
where,
l is the initial length of the solid
Δl is the change in length.
αl length expansion coefficient
ΔT is the temperature difference
Area Expansion:
ΔA/A=αA.ΔT
where,
A is the initial area of the solid
ΔA is the change in the area.
αA Area expansion coefficient
ΔT is the temperature difference
Volumetric Expansion:
ΔV/V=αV.ΔT
where,
V is the initial volume of the solid
ΔV is the change in volume.
αV volume expansion coefficient
ΔT is the temperature difference
Volumetric Expansion Coefficient
It is important that we consider the volumetric thermal expansion of substances since most of the things we use in real life are three-dimensional and thereby undergo three-dimensional expansion i.e. volumetric expansion.
Thermal Expansion Of Solids Examples:
One can observe a plethora of applications of Thermal expansion in day to day life. Some of them are:
- Metal hot water heating pipes should not be used in long straight lengths
- Metal framed windows need rubber spacers
- Large structures and mega constructions such as railways, bridges need expansion joints in the structures to avoid sub kink
- Thermometers are another example of an application of thermal expansion
Mercury Thermometer:
- Thermal expansion is the basic principle that a thermometer works on.
- The mercury in the reservoir at the bottom of the thermometer is immersed in a hot or cold object.
- On doing so, the mercury in the thermometer contracts and expands changing the level indicated on the thermometer.
- The thermometers are always calibrated and after a few minutes, the level of mercury inside becomes stable and unchanging.
- This new level with the calibrated thermometer tells us the temperature of the object we are measuring.
- The same principle of thermal expansion applies to gases as well.
- The constant volume gas thermometer is an example of the application of thermal expansion in gases.
Thermal Expansion of Fluids :
THERMAL EXPANSION IN LIQUID:
- Liquids expand when its atoms vibrate faster about their fixed points, but because the bonds between separate molecules are usually less tight they expand more than solids.
- This is the principle behind liquid-in-glass thermometers.
- An increase in temperature results in the expansion of the liquid which means it rises up the glass.
THERMAL EXPANSION IN GASES:
- When gases are heated pressure and volume change, gases have large thermal expansion because of large intermolecular distance between the molecules of the gas .
- There are two types of expansions of gases
1) Volume expansion of gas
2) Pressure expansion of gas
- Example of thermal expansion in gases can be observed in hot air baloons, when the gas is heated the baloon inflates.
Coefficients of cubical or volumetric thermal expansion of some common liquids:
Material Volumetric coefficient of expansion (10⁻⁴ °C⁻¹)
Mercury - 1.8
Engine Oil - 7.0
Petroleum - 10.0
Chloroform - 12.7
Benzene - 12.5