Thermal Expansion

The tendency of any matter to change the volume, shape, or even area due to temperature variation is known as thermal expansion. In simple words, an increase in temperature compels a material to increase its volume. The consequent increase of volume due to the increase in temperature is known as thermal expansion. There are several types of thermal expansion based on the molecular packaging of matter. This blog discusses thermal expansion in detail. In addition, it discusses the applications and examples of thermal expansion that one can find in daily lives.

Definition of Thermal Expansion

An increase in a material’s volume due to increased temperature defines thermal expansion. Also, it is the fractional change in volume or length of material about a temperature change. 

Types of Thermal Expansion Coefficients

There are three types of thermal expansion coefficients in physics. 

First, the linear expansion coefficient takes care of the thermal expansion of solid materials. It caters to the solid material’s length, thickness, and height. The thermal expansion coefficient takes care of the liquid and gaseous material. It is easier to explain the change in volume concerning the temperature change for a matter in liquid form. Different materials have different molecular packages and bonding forces. The thermal expansion coefficient is all about the varied characteristics of materials.

Linear Expansion

Linear expansion deals with the increase in the length of solid material when it experiences an increase in temperature. For example, consider a rod of length L, and a small amount of increase changes the temperature of the rod. The formula for linear expansion in this context would be:

ΔL = αLΔT

Where,

ΔT denotes the change in temperature.

ΔL denotes the change in length. 

αL denotes the linear coefficient of thermal expansion.

L denotes the original length.

‘a’ denotes the coefficient of thermal expansion of a given solid. Thus, the SI Unit for thermal expansion of solids is per degree Celsius, and according to the CGS system, it is per Kelvin. 

Volume Expansion

The expansion of the volume of a solid on being heated is known as the volume expansion. The formula for volume expansion is as follows:

ΔV  = αv V ΔT

Where, 

ΔT denotes temperature change.

 αv is the coefficient of volume thermal expansion.

V = area of the object in m3

ΔV = Change in volume in m3

Superficial or Area Expansion

If there is an increase in the surface area after increasing temperature due to heating, then the phenomenon is known as area expansion. The formula for area expansion in solids is as follows:

A0 (l + βt).

Where,

A0 is the area of the solid at 0 degrees celsius.

β denotes the coefficient of area expansion.

The unit for area expansion is given by per degree celsius or per kelvin.

Relation between thermal expansion coefficients

The following formula explains the three types of thermal expansion coefficients in a relationship.

6α = 3β = 2γ.

α denotes the linear expansion, β denotes the area expansion, and γ denotes the volume expansion. The values of these coefficients depend on the temperature and are not constant.

Applications and Thermal Expansion Examples 

The theory of thermal expansion is widely used in thermometers, riveting, and the removal of tight metal lids of jars. Due to thermal expansion, as the body’s temperature is recorded, the mercury expands unidirectionally.

In the case of removing tight metal lids, you may have immersed tight-lidded jars in warm water. After the jar warms, it is easier to open the lid. The expansion of the metal lid due to the increased temperature is the reason for the sudden easy removal of the tight metal lid. 

Before rivets are used to join the steel plates by forcing them through the plate holes, they are heated. After which, the end of the plates are hammered, and once the rivets cool down, they will grip the plates tightly.

Conclusion

Thermal expansion is the phenomenon following an increase in the length, volume, and area of a solid, liquid, or even gas upon an increase in temperature. The three different types of thermal expansion are linear, volume, and area expansion. There is a relationship between the three expansions denoted by the formula 6α = 3β = 2γ. Here, α, β, γ denote linear, superficial, and volume thermal expansion coefficients. There is an inverse connection between bond energy and thermal energy—the higher the melting point, the lower the thermal expansion of matter. Three applications of thermal expansion that we come across daily are riveting, opening tight metal lids by immersing the jar in warm water, and using a thermometer during fevers.