B.1 Thermal energy transfers

Objective notes

17 learning objectives

—B.1.1—Molecular states

• Describe solids, liquids and gases using molecular theory.

—B.1.2—Density

• Density: ρ=m/V.

—B.1.3—Temperature scales

• Use Kelvin and Celsius temperature scales.

—B.1.4—Temperature scale changes

• Temperature change has the same size in Kelvin and Celsius.

—B.1.5—Kelvin temperature and kinetic energy

• Kelvin temperature measures average particle kinetic energy: Ek=3/2 kBT.

—B.1.6—Internal energy

• Internal energy = intermolecular potential energy + random molecular kinetic energy.

—B.1.7—Thermal transfer direction

• Temperature difference sets the net direction of thermal energy transfer.

—B.1.8—Phase change

• Phase change changes particle behaviour via energy transfer at constant temperature.

—B.1.9—Specific heat and latent heat

• Use Q=mcΔT for temperature change and Q=mL for phase change.

—B.1.10—Thermal transfer mechanisms

• Conduction, convection and thermal radiation are the primary mechanisms for thermal energy transfer.

—B.1.11—Conduction

• Conduction: the difference in the kinetic energy of particles.

—B.1.12—Conduction rate

• Conduction rate depends on material, area and temperature gradient: ΔQ/Δt = kAΔT/Δx.

—B.1.13—Convection

• Qualitative description of thermal energy transferred by convection due to fluid density differences.

—B.1.14—Black-body radiation

• Black-body radiation power follows Stefan-Boltzmann law: L=σAT^4.

• Applies to emission of electromagnetic waves from a black-body surface.

—B.1.15—Apparent brightness

• Concept of apparent brightness b.

—B.1.16—Luminosity and brightness

• Apparent brightness relation: b = L/(4πd^2).

—B.1.17—Wien’s displacement law

• Use black-body spectrum and Wien’s law: λmaxT = 2.9x10^-3 m K.

• Use λmax to infer black-body temperature.