Thermal Expansion — A/L Physics

What must I remember about Thermal Expansion?

• Linear Expansivity (α): Fractional increase in length per unit temperature rise: α = ΔL / (L0 ΔT); Final length L = L0 (1 + α ΔT).
• Areal (β) and Volumetric (γ) Expansivity: Superficial (areal) expansivity β ≈ 2α; Volumetric expansivity γ ≈ 3α (for isotropic solids); Final volume V = V0 (1 + γ ΔT).
• Real vs Apparent Expansion of Liquids: When a liquid expands inside an expanding vessel: Real expansivity γ_real = Apparent expansivity γ_apparent + Volumetric expansivity of vessel γ_vessel.
• Thermal Stress: When a bar is rigidly clamped to prevent thermal expansion/contraction: Thermal Stress = F / A = Y * (ΔL / L0) = Y α ΔT, where Y is Young's modulus.

Test yourself (1 minute)

1. Anomalous Expansion of Water

   Water contracts as heated from 0 °C to 4 °C (density increases), reaching maximum density of 1000 kg/m³ at 4 °C; expands when heated above 4 °C; enables aquatic life survival under frozen lake surfaces.

2. Bimetallic Strip

   Composed of two metals with different expansivities (e.g., brass α_b > iron α_i) riveted together; bends toward the metal with lower expansivity upon heating; used in thermostats.

3. Density variation with temperature

   Density at temperature T: ρ = ρ0 / (1 + γ ΔT) ≈ ρ0 (1 - γ ΔT).

Practise Thermal Expansion questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 4: Thermal Physics

What should I study first?

What comes next?

Next in the syllabus

Where does Thermal Expansion fit in the syllabus?

Unit 4.2 · Year 1 · Term 2