Thermal expansion is defined as a phenomenon which is observed in solids, liquids, and gases. In thermal expansion, an object or a body expands on the basis of application of heat (temperature). Thermal expansion is the tendency of a body to change its dimension which are either in length, area, density, or volume due to heat When a substance is heated the kinetic energy of the substance increases.

Solid

• The particles of solid are always packed tightly.
• The gaps between the particles of a solid are very less and therefore the compression of solid is tough.
• The shape and volume of a solid is fixed.
• Solid is rigid in nature, hence the particles of solid only vibrate about their mean position and cannot move.
• Attractive force between the particles of solid is adamant.
• Example: solid ice, wood, sugar, rock, etc.

Liquid

• The particles of liquid are less tightly packed when compared to solids.
• Liquids have the ability to take the shape of the container in which liquids are kept.
• The particles of liquid have less space between them to move so the compression liquids are difficult but not as in solid.
• The Volume of Liquid is fixed but the shape of Liquid is not fixed.
• Rate of Diffusion in liquids is more as compared to solid.
• Example: water, milk, coffee, blood etc.

Gas

• The particles of gas are far from each other.
• The force of attraction between the particles of gases is almost negligible and hence they can move independently.
• The volume and shape of gas are not fixed.
• The particles of gas have more space between them to move so the compression gases are easy.
• The rate of diffusion is more as compared to solids and liquids.
• Example: air, oxygen, nitrogen, carbon dioxide, etc.

Thermal Expansion Types

There are three types of thermal expansions which we will learn.

1. Linear Expansion
2. Volume Expansion
3. Area Expansion

Linear Expansion

When the length changes because of heat then it is known as linear expansion.

L/L0=LT

Here, 

L= Length Change

L= Coefficient of length expansion

L0= Original Length

T= Difference in temperature

Coefficient of Linear Expansion is defined as rate of change of length per unit temperature.

A=dL/dT

Volume Expansion

When the volume changes because of heat then it is known as volume expansion.

V/V0=VT

V= Volume change

V= Coefficient of volume expansion

V0= Original Volume

T= Difference in temperature

The Coefficient of Volume Expansion is defined as the rate of change of unit volume per unit temperature.

Area Expansion

When the area changes because of heat then it is known as area expansion.

A/A0 =AT

Here,

A= Area change

A= Coefficient of Area expansion

A0 = Original Area

T= Difference in temperature

Coefficient of Thermal Expansion

Coefficient of Thermal Expansion is defined as a relative expansion of a material which is divided by the change in temperature.

Thermal Expansion of Solids

For solids, thermal expansion is expressed as a change in height, thickness, and length. Whereas for both liquids and gases, the coefficient of volumetric expansion is more useful. In general, if the material is a fluid (liquid or gas), we can determine it in terms of volume change.

Applications of thermal expansions

There are many applications of thermal expansions some of which are as follows

1. Thermal expansion used in thermometers to measure the temperature.
2. Thermal expansion is used for the removal of tight lids.
3. Rubber spacers are required for windows with metal-frame.

Mercury Thermometer

Thermal expansion is the basic principle on which a thermometer works. The mercury in the reservoir which is present at the bottom of the thermometer is immersed in a cold or hot object. After that the mercury in the thermometer expands and contracts and changes the level which is indicated on the thermometer.

Conclusion

Thermal expansion is defined as a phenomenon which is observed in solids, liquids, and gases. In thermal expansion, an object or a body expands on the basis of application of heat (temperature).

The particles of solid are packed tightly.

The gaps between the particles of a solid are very less and therefore the compression of solid is tough.

The particles of liquid are less tightly packed when compared to solids.

Liquids have the ability to take the shape of the container in which liquids are kept.

The force of attraction between the particles of gases is almost negligible and hence they can move independently.

The particles of gas have more space between them to move so the compression gases are not much difficult.

The Coefficient of Linear Expansion is formulated as A=dL/dT

The Volume Expansion is formulated as V/V0=VT 

The Coefficient of Thermal Expansion is defined as a relative expansion of a material which is divided by the change in temperature.

All materials always have different thermal expansion coefficients.

When a substance is heated the molecules of the substance start moving or vibrating.

Thermal expansion used in thermometers to measure the temperature.

There are three types of thermal expansions which we will learn.

1. Linear Expansion
2. Volume Expansion
3. Area Expansion