Is the internal energy of a system the same as the heat it contains?
No — a system doesn't 'contain heat'; internal energy is the total kinetic and potential energy of its particles, changed by heating or doing work. Learn it step by step →
Thermal Physics is a core part of A-Level Physics. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Kinetic theoryModel treating gas as fast-moving particles.
Mean square speedAverage of v² across all particles.
Boltzmann constantk = 1.38 × 10⁻²³ J/K = R / N_A.
Mean KE½ m c² = 3/2 kT per molecule.
Internal energySum of KE + PE of all particles.
Monatomic gasU = 3/2 N k T (only translational KE).
HeatEnergy transferred due to temperature difference.
Specific heat capacityEnergy per kg per K: c = Q / (mΔT).
Q = m c ΔTHeat to change temperature of mass m.
Latent heatEnergy for phase change at fixed T.
L_fSpecific latent heat of fusion (solid↔liquid).
L_vSpecific latent heat of vaporisation (liquid↔gas).
Ideal gasPoint particles with elastic collisions only.
PressureForce per unit area: p = F/A, in pascals.
What your exam board covers
Where Thermal Physics sits in each exam board's specification. Tap a board to see what it lists.
AQAFurther mechanics and thermal physics (A-level only)Spec 7408
Periodic motion (circular motion and simple harmonic motion)
Thermal physics (ideal gases and molecular kinetic theory)
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Is the internal energy of a system the same as the heat it contains?✗ Yes — internal energy is just the stored heat in the object.✓ No — a system doesn't 'contain heat'; internal energy is the total kinetic and potential energy of its particles, changed by heating or doing work.
When energy is 'lost' as heat due to friction, what has really happened?✗ Energy has been used up and no longer exists.✓ Energy has been transferred to the thermal store of the surroundings — it's not destroyed, just dissipated.
What does specific latent heat measure?✗ The energy required to raise the temperature of 1 kg by 1 degree.✓ The energy required to change the state of 1 kg of a substance without changing its temperature.
Why does a metal spoon in hot water heat up faster than a wooden one?✗ Metal heats up faster because it has a lower specific heat capacity, requiring less energy per degree.✓ Metals have higher thermal conductivity, so heat is transferred more rapidly through them.
Practise Thermal Physics — free games
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