Thermal Expansion | Physics for GCSE/IGCSE - Year 11 PDF Download

Thermal Expansion

• When substances are heated, they undergo expansion.
• This expansion occurs due to the acceleration of molecular movement or vibration.
• Consequently, molecules collide more frequently, exerting force on each other, and thus pushing each other farther apart.

• It's important to note that during this process, it's the volume occupied by the molecules that expands, while the molecules themselves maintain their original size.
• Thermal expansion is evident across solids, liquids, and gases.
• When temperature rises (while keeping pressure constant):
  • Solids exhibit the least expansion.
  • Gases demonstrate the most significant expansion.
  • Liquids experience expansion levels falling between those of solids and gases.

Thermal Expansion in Terms of Particles

• Molecules themselves do not undergo expansion, but rather the space between them increases.
• Heating solids, liquids, and gases results in:
  • Expansion occurring primarily in the space between molecules.
  • Solids, liquids, and gases all experiencing thermal expansion.

Uses & Consequences of Thermal Expansion

The thermal expansion of materials can lead to beneficial uses as well as undesirable outcomes.

Applications

• Thermometers utilize the expansion of liquids to gauge temperature.
• Temperature-activated switches operate based on the bending of a bimetallic strip, composed of two metals expanding at different rates, at specific temperatures.

The bimetallic strip will bend upwards when heated, closing the circuit

Consequences

• When solid materials heat up, they have a tendency to expand, potentially leading to buckling under extreme heat stress.
• Examples of materials susceptible to buckling due to thermal expansion are metal railway tracks, road surfaces, and bridges.
• To mitigate the risk of damage from expansion, structures prone to buckling are designed with intentional gaps to accommodate the expansion without causing harm.