Thermal Expansion — A/L Physics

Linear Expansion The increase in length of a solid when its temperature rises. When a solid rod is heated, its atoms vibrate more vigorously, increasing the average separation between them. This results in a proportional increase in length, directly dependent on the original length and the temperature change. For example, railway tracks have expansion gaps to prevent buckling on hot days.

Area (Superficial) Expansion The increase in surface area of a solid when heated. For a thin plate or sheet, the area expands in two dimensions. The coefficient of area expansion is approximately twice the coefficient of linear expansion for isotropic materials. A bimetallic strip in a thermostat uses this principle to bend and break or make an electrical circuit.