Physics 9702 · syllabus 14
Cambridge A Level Physics 9702 — Temperature topical past papers
What temperature means and how it is measured: thermal equilibrium, the Celsius and kelvin scales, specific heat capacity and specific latent heat.
- Questions
- 103
- Years
- 2009–2026
- With mark scheme
- 100%
- Questions 2022–2026
- 40
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What Temperature covers
Thermal energy flows from a region of higher temperature to one of lower temperature, and when there is no net flow between them the two are in thermal equilibrium at the same temperature. Any property that varies with temperature can be used to measure it: the volume of a gas at constant pressure, the resistance of a metal, the e.m.f. of a thermocouple or the density of a liquid. Thermometers based on different properties agree at their calibration points but need not agree between them.
The thermodynamic scale avoids that problem because it does not depend on the property of any particular substance. Its zero, absolute zero, is the lowest possible temperature, and a temperature in kelvin equals the Celsius value plus 273.15. A temperature change has the same size in kelvin as in degrees Celsius.
Heating a substance either raises its temperature or changes its state. Specific heat capacity is the energy needed per kilogram for each kelvin of temperature rise; specific latent heat is the energy per kilogram to change state at constant temperature, for melting (fusion) or boiling (vaporisation). This is A Level content, examined on Paper 4, and it prepares the ground for ideal gases and thermodynamics.
In the syllabus
The headings this topic has in the Cambridge International 2025–2027 syllabus, as the board prints them.
- 14 Temperature
- 14.1 Thermal equilibrium
- 14.2 Temperature scales
- 14.3 Specific heat capacity and specific latent heat
What you should be able to do
- Explain thermal equilibrium in terms of net energy transfer
- Convert between degrees Celsius and kelvin
- Name physical properties used to measure temperature and explain why the thermodynamic scale does not depend on any of them
- Use Q = mcΔθ and Q = mL in problems with more than one stage of heating
- Find a specific heat capacity or latent heat from heater power, time and mass data, and explain the effect of energy losses
- Explain why the temperature stays constant during a change of state
Key ideas
- T/K = θ/°C + 273.15; a change of 1 K equals a change of 1 °C
- Specific heat capacity: Q = mcΔθ, with c in J kg⁻¹ K⁻¹
- Specific latent heat: Q = mL, with L in J kg⁻¹, for fusion (melting) or vaporisation (boiling)
- Electrical heating: energy supplied = VIt = Pt
How Temperature has been examined
From 2022 to 2026, Temperature was on Paper 4 · A Level Structured Questions in 10 of 11 exam series, worth about 12% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice | 1 | 1% | 1 of 11 |
| Paper 4 · A Level Structured Questions | 39 | 12% | 10 of 11 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 9. Some of these questions sit in a bank chapter that also covers a neighbouring topic, so the counts can run a little high.
Filed in Momentum under: Temperature, Thermal Properties of Materials.
A worked example
A 2.0 kW electric kettle of negligible heat capacity holds 0.25 kg of water at 20 °C. How long does it take to bring the water to 100 °C and then boil away 0.050 kg of it? Take c = 4200 J kg⁻¹ K⁻¹ and L = 2.26 × 10⁶ J kg⁻¹ for water, and assume no energy is lost.
- Heating to boiling point: Q₁ = mcΔθ = 0.25 × 4200 × 80 = 8.4 × 10⁴ J
- Boiling away 0.050 kg: Q₂ = mL = 0.050 × 2.26 × 10⁶ = 1.13 × 10⁵ J
- Total energy: 8.4 × 10⁴ + 1.13 × 10⁵ = 1.97 × 10⁵ J
- Time: t = Q/P = 1.97 × 10⁵ / 2000 = 98.5 s
Answer: About 99 s
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Adding 273 to a temperature change — a rise of 20 °C is a rise of 20 K, not 293 K
- Using the latent heat of fusion for boiling, or the reverse — vaporisation needs far more energy per kilogram because the molecules must be separated completely
- Assuming all the heater's energy goes into the sample — losses to the surroundings make the calculated c or L larger than the true value
- Saying temperature measures the total internal energy of an object — two objects at the same temperature can hold very different amounts of internal energy
- Forgetting a warming stage before a change of state, such as heating ice from −10 °C to 0 °C before it can melt
Exam technique
- Set out multi-stage heating as a sum of separate energies, warming, changing state and warming again, with each line labelled
- When explaining a constant temperature during melting or boiling, say the energy increases the potential energy of the molecules, not their kinetic energy
- Give c in J kg⁻¹ K⁻¹ and L in J kg⁻¹; a missing or extra K⁻¹ shows the two have been confused
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.