THERMAL EXPANSION

Thermal expansion is the increase in volume of a substance due to increase in temperature.

When a material is heated, its volume increases slightly.

The particles vibrate faster and take more space.

When it gets cold, the vibrations become smaller and take less space. Hence contraction.

Liquids expand more than solids.

Gases expand more than liquids.

Material Increase in length due to 100oC temperature increase

Invar (metal) 0.1mm

Pyrex glass 0.3mm

Platinum alloy 0.9mm

Glass 0.9mm

Concrete 1mm

Steel 1mm

Brass 2mm

Aluminium 3mm

Everyday considerations of thermal expansion Buildings (walls and fences) are built with an

allowance for expansion to avoid cracks.

Steel rods are used to reinforce concrete because they expand equally.

Pyrex glass is used in the lab for heating instead of ordinary glass.

Thermometers work on the principle of thermal expansion.

Bimetallic strips and thermostats use thermal expansion to control circuits.

Group discussion What are some of the activities we do everyday that

requires us to consider thermal expansion?