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Detailed notes on Thermal Physics for Cambridge IGCSE Coordinated Science, covering key concepts, explanations, examples, and exam-focused revision points.
Temperature is measured by thermometric properties — physical quantities that change measurably with temperature. Cambridge tests thermometer types, their advantages, and the Celsius scale vs Kelvin scale.
Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).
Different thermometers suit different ranges, response times, and situations.
Thermometric properties: A useful thermometric property must:
Liquid-in-glass thermometer:
Thermocouple thermometer:
Thermistor:
Clinical thermometer:
Choosing a thermometer:
| Requirement | Best thermometer |
|---|---|
| Very high temperature | Thermocouple |
| Very low temperature | Alcohol-in-glass |
| Fast response | Thermocouple or thermistor |
| Remote sensing | Thermocouple or thermistor |
| Simple/cheap | Liquid-in-glass |
The Celsius scale is defined by ice and steam points; Kelvin scale is the absolute scale.
Celsius scale:
Kelvin (absolute) scale:
T(K) = T(°C) + 273
Key temperature conversions:
| Celsius | Kelvin |
|---|---|
| −273°C | 0 K |
| 0°C | 273 K |
| 20°C | 293 K |
| 100°C | 373 K |
| 1000°C | 1273 K |
Verbatim phrases and definitions Cambridge mark schemes credit.
Paper 4: 'Convert 37°C to Kelvin' (1 mark — 310 K). 'State ONE advantage of a thermocouple over a liquid-in-glass thermometer' (1 mark — wider range / faster response / can be used remotely). 'State the thermometric property used in a liquid-in-glass thermometer' (1 mark — volume/length of liquid). MCQ: choosing the best thermometer for a given application.
Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (P3); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.
Step-by-step solutions to past-paper-style questions on measurement of temperature , written exactly the way a tutor would explain them at the board.
Question
Describe how to calibrate a liquid-in-glass thermometer using two fixed points.
Step-by-step solution
Step 1
Immerse the thermometer bulb in a mixture of pure melting ice and water at standard atmospheric pressure. Mark the liquid level — this is 0°C (the lower fixed point).
Step 2
Immerse the bulb in steam above boiling pure water at standard atmospheric pressure. Mark the liquid level — this is 100°C (the upper fixed point).
Step 3
Divide the distance between the two marks into 100 equal divisions. Each division represents 1°C.
Answer
Mark 0 °C (ice point) and 100 °C (steam point) at standard pressure, then divide the interval into 100 equal divisions.
Question
Suggest two advantages of a thermocouple thermometer over a liquid-in-glass thermometer for measuring the temperature of a small, rapidly changing heat source.
Step-by-step solution
Step 1
A thermocouple has a very small thermal mass (junction is tiny metal wires), so it responds rapidly to temperature changes — suitable for rapidly fluctuating temperatures.
Step 2
A thermocouple can measure very high temperatures (well above 300°C) at which a liquid-in-glass thermometer would break or the liquid would boil.
Answer
Faster response time (small thermal mass) and wider temperature range (can measure very high temperatures).
Question
A resistance thermometer has resistance 200Ω at 0°C and 280Ω at 100°C. When placed in a liquid, its resistance is 248Ω. Assuming a linear response, calculate the temperature of the liquid.
Step-by-step solution
Step 1
Change in resistance over full range: 280−200=80Ω corresponds to 100°C.
Step 2
Change at the unknown temperature: 248−200=48Ω.
Step 3
Temperature by proportion.
θ=8048×100=60°C
Answer
θ=60°C
Examiner tip
This interpolation method works for any thermometric property that varies linearly with temperature.
The formulae you need to memorise for measurement of temperature on the Cambridge IGCSE 0654 paper, with every variable defined in plain English and a note on when to use it.
θ=X100−X0Xθ−X0×100°C
When to use
Reading a thermometer calibrated with two fixed points assuming a linear response.
T(K)=T(°C)+273
When to use
Converting between Celsius and kelvin scales (required for all gas law calculations).
Definitions to memorise and the exact keywords mark schemes credit for measurement of temperature answers — sharpened from recent examiner reports for the 2026 0654 sitting.
A physical property that changes measurably and (ideally) linearly with temperature and can be used to measure it. Examples: length of a liquid column, electrical resistance, EMF of a thermocouple.
A standard, reproducible temperature used to calibrate thermometers. The lower fixed point is 0°C (pure ice point); the upper is 100°C (pure steam point), both at standard atmospheric pressure.
A thermometer that uses the EMF generated at the junction of two different metals as its thermometric property. Advantages: fast response, wide range, can be made very small.
A temperature scale with 0°C at the ice point and 100°C at the steam point of water at standard atmospheric pressure.
The traps other students keep falling into on measurement of temperature questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.
Why it happens
Students know the temperatures but forget that boiling/freezing points depend on pressure.
How to avoid it
Always state 'at standard (atmospheric) pressure' when describing fixed points. Boiling point of water changes with pressure.
Why it happens
Interpolation calculations assume linearity, but students do not flag this.
How to avoid it
Write 'assuming a linear relationship' before applying the interpolation formula.
Why it happens
Students convert correctly but then accidentally use the original Celsius value.
How to avoid it
After converting, cross out the Celsius value and only use the kelvin value in gas law calculations.
The things students keep getting wrong in this sub-topic, answered.