We all know that when different substances get exposed to increased heat, they react in different ways. When solids, liquids, or gases undergo some temperature change, their dimensions and volumes also tend to change. Thermal expansion refers to the expansion and growth of the dimensions of solids, liquids, or gases when their temperature undergoes an increase. Let us look at some examples of thermal expansion that we come across in our daily lives.

Thermal Expansion

The ability of matter to change its form, area, volume, and density in reaction to a change in temperature is known as thermal expansion. Transitions between phases are not included.

The temperature monotonic affects a material’s average molecular kinetic energy. When a solid is heated, the atoms begin to vibrate and move more, increasing their space. 

Types of Thermal Expansions

Thermal expansion can manifest in three different ways: in the form of linear, areal and volume expansion.

• Linear Expansion

In solids, thermal expansion occurs in the form of an increase in length. For example, if we consider the rod of length to increase due to increased temperature. The linear expansion is given by:

 ΔL = 𝛼L ΔT Lwhere,

• ΔL illustrates the difference in length 
• L is the original length
• ΔT is the temperature change
• 𝛼 is defined as the linear coefficient of thermal expansion
• In the CGS unit, the linear coefficient is represented by celsius-1.
• In the SI unit, the linear coefficient ‘𝛼’ is represented by kelvin-
• 1.Area Expansion

The thermal area expansion coefficient links a change in temperature to a change in the area dimensions of a substance. The fractional change in area per degree of temperature change is what this term refers to.

Coefficient

Areal expansions are expressed through coefficients, the fractional change in area per degree of temperature change. Therefore, the coefficient denotes the rate of area change per unit degree change in temperature.

The formula is expressed as ΔA = 2αAAΔT

Where A is the initial area,

ΔT is the temperature change,

ΔA is the change in area,

αA is the coefficient of area expansion.

• Volume Expansion

We may express the volumetric (or cubical) thermal volume expansion coefficient as follows, ignoring the effects of pressure on a solid:

The formula is expressed as ΔV = βV1 ΔT

Wherein:

• V1 is the initial volume,
• ΔT is the temperature change,
• ΔV is the change in volume,
• β is the coefficient of volumetric expansion.

Thermal Expansion in Metals

Thermal expansion is all about expansion on heating and contraction on cooling. On heating, the dimension of the objects will change. Based on the changes that occur in the body, these are the following observations:-

• If the length of the objects gets expanded, it is called linear expansion.
• On heating, if the length and breadth of the object get changed, it is called area expansion.
• If any objects expand on both sides on heating and lead to an increase in volume, it is called volume expansion.
• Some examples of thermal expansion in solids are molten rods, metal-framed windows, thermometers, and railway works where expansion is needed in joints of the structure. 

Some important points related to Thermal expansion of solids

• If the volume of the objects increases due to an increase in temperature, then it is known as thermal expansion.
• The change that occurs in an object’s volume, area, or length is called thermal expansion.
• In the case of a solid, linear expansion is more common.
• The expansion may increase height, length, or thickness in all solids, liquids, and gases.
• Volumetric expansion is more common in liquid and gases.
• The binding forces are different in different materials, and it has a different expansion coefficient.
• If the object has a well structural configuration, its expansion coefficient will be uniform throughout the objects.
• If the object does not have a uniform structural configuration, it has a different coefficient of expansion(CTE).
• Temperature increase leads to change in shape. Hence the CTE increases.
• Softer metals have higher CTE.
• Harder materials like tungsten have lower CTE.

Conclusion

When a solid is heated, the atoms around its fixed points vibrate faster. As a result, the comparative enlargement of solids when heated is slight. When different substances are exposed to heat, they react in different ways. When solids, liquids, and gases undergo an increased temperature change, their dimensions and volumes also tend to change. Thermal expansion refers to the expansion and growth of the dimensions of solids, liquids, or gases when their temperature undergoes an increase.

Thermal expansion, which does not include phase changes, is the tendency of matter to alter its form, area, volume, and density in response to a change in temperature.