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Physics Revision Guides
A-Level Revise Aid: This resource is designed to support your revision and may contain errors. If you find a discrepancy with your class teaching, your teacher is correct -- please let us know at alevelrevise@scott.scottrix.co.uk.

Thermal Physics

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

A-Level Physics revision: Thermal Physics. Learning objectives, key points, worked examples and practice questions across AQA, Edexcel, OCR, WJEC and CCEA.

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πŸ“Œ Key Points

Key Fact: Internal energy U = Σ(KE + PE) of molecules; Temperature ∝ mean KE per molecule
Key Fact: Q = mcDeltaΞΈ (no phase change); Q = mL (phase change); L_fusion, L_vaporisation
Key Fact: 1st law: DeltaU = Q + W; W = ∫PdV (work done ON gas); Q +ve into system, W +ve on system
Key Fact: Ideal gas: pV = nRT = NkT; Boyle p∝1/V (isothermal), Charles V∝T (isobaric), Pressure p∝T (isochoric)
Key Fact: Kinetic theory: pV = β…“Nm<c^2> -> p = ⅓ρ<c^2>; <c^2> = 3RT/M
Key Fact: RMS speed: c_rms = sqrt(3RT/M); M = molar mass in kg/mol
Key Fact: Degrees of freedom: monatomic 3 (translational); diatomic 5 (+2 rotational) at room temp
Key Fact: Equipartition: each quadratic term contributes Β½kT per molecule

🎯 Learning Objectives

  • Distinguish heat, internal energy, and temperature
  • Use specific heat capacity c and specific latent heat L
  • Apply first law: DeltaU = Q + W (sign conventions)
  • Use ideal gas laws: Boyle, Charles, Pressure, Combined, PV = nRT
  • Understand kinetic theory: pressure from molecular collisions
  • Relate microscopic (molecular) to macroscopic (PV=nRT)
  • Calculate root-mean-square speed: c_rms = sqrt(3RT/M)
  • Understand degrees of freedom and equipartition of energy

πŸ’‘ Worked Example

Exam-Style Question

Question: 2 moles of ideal gas at 300 K compressed isothermally from 0.02 m^3 to 0.01 m^3. Find work done

Model Answer:

Isothermal: W = ∫PdV = ∫(nRT/V)dV = nRT ln(Vβ‚‚/V₁) = 2x8.31x300xln(0.5) = -3457 J. Work done ON gas = +3457 J

❓ Practice Questions

Questions:

  • Heat to raise 500 g water from 20 deg C to 80 deg C (c=4180)
  • 1 mole gas at 27 deg C, V=0.022 m^3. Find pressure
  • Explain why C_p > C_v for ideal gas
  • RMS speed of Nβ‚‚ at 300 K (M=0.028 kg/mol)
  • Derive pV = β…“Nm<c^2> from momentum change on wall

🎬 Video Resources

πŸ“„ Past Papers & Exam Resources

πŸ”— Further Reading & Resources