Thermal and Linear Expansion

Introduction

We all know that when different substances get exposed to increased heat, they tend to react in different ways. When solids, liquids, or gasses 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 gasses when their temperature undergoes an increase. Let us look at some everyday examples of thermal expansion that we come across in our daily lives.

Examples of Thermal Expansion

1. Public roads crack after undergoing vigorous temperature increases and fluctuations due to the weather.
2. Electric power wires tend to sag after their materials expand.
3. Glass windows with metal frames require rubber strips to be kept in between to avoid thermal expansion.
4. Joints in railway tracks or bridges are slightly larger to consider thermal expansion.
5. On hot days, tyres can burst due to the thermal expansion of the air inside them.

Types of Thermal Expansion

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

Linear Expansion

When a substance is exposed to heat, it reacts and increases in length. Linear expansion refers to the change in length with respect to its original length on account of increased temperature change,

Coefficient

Linear expansions are expressed through coefficients, which is the per degree Celsius, or change in the length of a 1 unit long material when there is a 10°C temperature increase. Therefore, the coefficient denotes the rate of change of unit length per unit degree change in temperature.

The formula is expressed as αLL1 = dL / dT,

wherein:

• αL is the coefficient of linear expansion,
• L1 is the initial length of the material,
• dL is the unit change in length, and
• dT is the unit change in temperature.

SI Unit and Dimension

The SI unit of coefficient of linear expansion can be expressed as °C-1 (Celsius) and °K-1 (Kelvin).

Functioning

The expansion of materials depends on the collective force between the atoms and particles in it. If this collective force is high, the linear expansion of the material will be low, even if the temperature is drastically increased. Therefore, the coefficient of linear expansion is an in-built property of a material, and thus it will vary from one type of material to another. This is why soft metals tend to expand quickly because the collective force between the atoms is low.

Value of Coefficient of Linear Expansion for Some Compounds

Every compound has varying values than others, based on its properties. For example, solids have a high coefficient because of the increased collective force between the atoms in them. Therefore, hard solids have a higher coefficient within the range of 10^-7/K, whereas on the other hand, organic liquids are within the range of 10^-3/K. The table below showcases the values for various metals.

S No.	Metals	αL at 20 ° C (10-6/K)
1.	Aluminium	23.1
2.	Brass	19
3.	Carbon Steel	10.8
4.	Diamond	1
5.	Copper	17
6.	Gold	14
7.	Ice	51
8.	Iron	11.8
9.	Mercury	61
10.	Steel	From 11 to 13
11.	Water	69
12.	Silicone	2.56

Areal Expansion

When a substance’s surface area expands as the temperature rises, it is known as areal expansion. Superficial expansion is another name for areal expansion.

Coefficient

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

The formula is expressed as ΔA = 2αAAΔT

Wherein:

• A is the area
• ΔA is the change in area
• αA is the area expansion coefficient
• ΔT is the temperature difference

SI Unit

The SI unit of coefficient of linear expansion can be expressed as Unit Area and °K^-1 (Kelvin).

Functioning

Areal expansion is a two-dimensional material expansion. The temperature of the object influences how much it expands. When the temperature of an object changes, the volume of the object adjusts to cause an increase in area.

Volume Expansion

Volume/ volumetric/ cubical expansion takes place when the increased temperature acting on a gas, solid, or liquid increases the volume of the material.

Coefficient

Volumetric expansions are expressed through coefficients, which is the fractional change in volume per degree of temperature change. Therefore, the coefficient denotes the rate of change of volume per unit degree change in temperature.

The formula is expressed as ΔV = βV1 ΔT

Wherein:

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

SI Unit

The SI unit of coefficient of volumetric expansion can be expressed as Unit Volume and °C^-1.

Functioning

Volumetric expansion is a three-dimensional material expansion. The temperature of the item influences how much its volume expands. When the temperature of the object changes, the volume increases as a reaction.

Conclusion

When different substances are exposed to heat, they react in different ways. When solids, liquids, and gasses 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 gasses when their temperature undergoes an increase. Linear expansion is the fractional change in length with respect to its original length. The formula is expressed as αLL1 = dL / dT. When a substance’s surface area expands as the temperature rises, it is known as areal expansion. Superficial expansion is another name for areal expansion. The formula is expressed as ΔA = 2αAAΔT. Volume/ volumetric/ cubical expansion takes place when the increased temperature acting on gas, solid, or liquid increases the volume of the material. The formula is expressed as ΔV = βV1 ΔT. All materials possess different thermal expansion properties. Understanding the expanding ability with an increase in temperature for various materials is crucial in order to use them in an appropriate situation.