The area of a solid is increased with the increase of temperature.It is called superficial expansion.

Let initial surface area of a solid at **θ _{1}** temperature = A

_{1}

When the temperature is increased to **θ _{2}** the final surface area =A

_{2}

So, Increase in temperature = **θ _{2} – θ_{1}**

And increase in area = **A _{2} – A_{1}**

The coefficient of superficial expansion is expressed by the symbol β

Superficial expansion, **β = [(A _{2} – A_{1}) / A_{1}(θ_{2} – θ_{1})] ….. ………. ………(1)**

**[Increase in surface area / (Initial area x increase of temperature)]**

In equation (1) if the surface area A_{1} = 1 m^{2} and the increase of temperature (**θ _{2} – θ_{1})** = 1K is considered, then the increase in surface area β =

**A**=increase in surface area.

_{2}– A_{1 }So, the increase in surface area of 1 m^{2} surface area of a solid for the rise of temperature 1K is called the coefficient of superficial expansion of the material of that solid. Its unit is K^{-1}. The coefficient of superficial expansion of copper is **33.4 x 10 ^{-6} K^{-1}**. It means that if the temperature of a copper body is increased through 1K, then the increase in surface area of copper is

**33.4 x 10**

^{-6}m^{2}.