Heat Transfer — A/L Physics

What must I remember about Heat Transfer?

• Mechanisms of Heat Transfer: Conduction (molecular vibration and free electron diffusion without bulk macroscopic material motion; primary in solids), Convection (bulk fluid circulation driven by density differentials; liquids and gases), Radiation (emission of electromagnetic waves requiring no material medium).
• Thermal Conduction (Fourier's Law): Rate of heat flow through a conductor of cross-section A and temperature gradient dT/dx: dQ/dt = k A (T_hot - T_cold) / L, where k is thermal conductivity (W·m⁻¹·K⁻¹).
• Newton's Law of Cooling: Rate of heat loss of a body by combined convection and radiation is directly proportional to temperature difference between body and surroundings (provided difference is small, ΔT < 30 °C): dQ/dt = -h A (T - T_s); Rate of cooling dT/dt = -k' (T - T_s).
• Thermal Radiation (Stefan-Boltzmann Law): Total radiant power emitted by a black body of surface area A at absolute temperature T: P = e σ A T⁴, where σ = 5.67 × 10⁻⁸ W·m⁻²·K⁻⁴ and e is emissivity (e = 1 for ideal black body); Net heat exchange with environment at T_s: P_net = e σ A (T⁴ - T_s⁴).

Test yourself (1 minute)

1. Wien's Displacement Law

   The wavelength λ_max corresponding to peak radiant intensity of a black body is inversely proportional to absolute temperature: λ_max * T = b (constant b ≈ 2.898 × 10⁻³ m·K).

2. Prevost's Theory of Heat Exchange

   All bodies at any temperature above absolute zero (0 K) continuously emit and absorb thermal radiation simultaneously.

3. Thermos (Vacuum) Flask Design

   Double glass walls with vacuum between them eliminates conduction and convection; silvered interior walls reflect thermal radiation back, minimizing radiation loss.

Practise Heat Transfer 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 Heat Transfer fit in the syllabus?

Unit 4.6 · Year 1 · Term 2