What is Expansion of Solids?

With the application of heat the length, area and volume of solid substance expands.

Linear expansion of solid and coefficient of linear expansion:

When heat is applied to a solid substance elongation of its length occurs towards a definite direction and the expansion along its length is called linear expansion.

Let the length of a bar at θ₁ temperature be l₁ and at θ₂ temperature the length be 1₂.

Increase in length = I₂ – I₁

And increase of temperature = θ₂ – θ₁

The coefficient of linear expansion is denoted by a and it can be expressed as,

α = (I₂ – I₁)/ I₁ (θ₂ – θ₁) … …… ……(1)

= [Increase in length / (Initial length x increase of temperature)]

In equation (1), if the initial length I₁ = lm and increase of temperature, θ₂ – θ₁ = 1K, then  α = (I₂ – I₁) = increase in length.

So, the increase in length of a solid rod of lm for a rise of temperature 1K is defined as the coefficient of linear expansion of the material of the solid.

Its unit is K^-1. The coefficient of linear expansion of copper is 16.7 x 10^-6 K^-1 means if the temperature of copper rod is raised through 1K, then its length increases by 16.7 x 10^-6 m.