What is areal expansion? Give the definition and unit of the coefficient of areal expansion.

(N/A) Areal expansion (or superficial expansion) is the increase in the surface area of a solid body due to an increase in its temperature.
Definition of coefficient of areal expansion $(\beta)$: It is defined as the fractional change in area per unit change in temperature.
Mathematically,$\beta = \frac{\Delta A}{A_0 \Delta T}$,where $\Delta A$ is the change in area,$A_0$ is the initial area,and $\Delta T$ is the change in temperature.
Unit: The $SI$ unit of the coefficient of areal expansion is $\text{K}^{-1}$ or $^\circ\text{C}^{-1}$.