In simple terms
A friendly intro before the formal notes — no formulas yet.
Temperature scales
Cambridge 9702 Paper 4 — Temperature scales (14.2). Senpai Corner diagram-backed pilot with premium structure and live visuals.
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14.2 Temperature scales.
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A thermometer is any device that is used to measure temperature.
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There are many types of thermometer e.g. liquid-in-glass. thermocouple, bimetal thermocouple, etc.
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You will need to be able to give an example for each of the above types and explain how it works.
What this topic covers
The official Cambridge syllabus points this lesson works through.
- 14.2.1
Understand that a physical property that varies with temperature may be used for the measurement of temperature and state examples of such properties, including the density of a liquid, volume of a gas at constant pressure, resistance of a metal, e.m.f. of a thermocouple
- 14.2.2
Understand that the scale of thermodynamic temperature does not depend on the property of any particular substance
- 14.2.3
Convert temperatures between kelvin and degrees Celsius and recall that
- 14.2.4
Understand that the lowest possible temperature is zero kelvin on the thermodynamic temperature scale and that this is known as absolute zero
Explore the concept
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Step 1
14.2 Temperature scales.
2 more simulations for this topic — run them in the Simulations section below
Simulations
Every simulation here runs the real model — try the steps on a card, then check what you see against the notes.
2 simulations · 2 to start with
Start herein this order — each one shows a different piece of the topic
- 3JCN PhysicsStart here · 19702 14.1 · 9702 14.2 · 9702 15.2
Measure Abs Zero T
Measure absolute zero by plotting pressure against temperature for a gas
Why this one: Take your own p–T readings, plot them and find where the line cuts the temperature axis.
Try this
- Plot pressure against temperature for the gas at several temperatures.
- Extend the straight line to zero pressure and read the intercept.
Look for Every constant-volume line extrapolates to the same intercept, about -273 °C.
3JCN Physics Simulation by Thomas Nguyen · CC BY 4.0
- 3JCN PhysicsStart here · 29702 14.1 · 9702 14.2 · IB B.1
Thermometer
Calibrate a liquid-in-glass thermometer between fixed points
Why this one: Fix the ice and steam points: Celsius needs two fixed points, Kelvin needs only absolute zero and one more.
Try this
- Mark the liquid level at the ice point and at the steam point.
- Divide the scale between the fixed points and read an unknown temperature.
Look for A temperature scale needs two fixed points, and the reading assumes the liquid expands linearly between them.
3JCN Physics Simulation by Thomas Nguyen · CC BY 4.0
Key formulas
Tap any symbol to reveal exactly what it means and its units.
Tap a symbol — great for exam definitions
Full topic notes
Formal explanation with the rigour you need for the exam.
The Kelvin Scale: An Absolute Foundation
The Kelvin scale is the absolute temperature scale and the SI unit for temperature. It's unique because its zero point, known as absolute zero (0 K), represents the lowest possible energy state for particles, where they theoretically have zero kinetic energy. This makes Kelvin measurements independent of any specific substance's properties.
14.2 Temperature scales.
A thermometer is any device that is used to measure temperature.
There are many types of thermometer e.g. liquid-in-glass. thermocouple, bimetal thermocouple, etc.
You will need to be able to give an example for each of the above types and explain how it works.
The Kelvin scale is also called the thermo dynamic scale.
Absolute zero is defined as the temperature at which atoms and molecules in all substances have zero kinetic and potential energy.
The Celsius Scale: Relative and Familiar
In contrast to Kelvin, the Celsius scale (°C) is a relative scale, based on fixed points related to pure water. It sets 0°C as the melting point of ice and 100°C as the boiling point of water, both at standard atmospheric pressure. While familiar, Celsius temperatures often need converting for advanced physics formulas.
Celsius (°C) is a relative temperature scale.
Defined by fixed points: 0°C (ice melting) and 100°C (water boiling).
These points are at standard atmospheric pressure.
A change of 1 Kelvin equals a change of 1 degree Celsius (ΔK = Δ°C).
Converting Between Scales
You'll frequently need to convert between Celsius and Kelvin, especially when working with thermal physics equations. Remember, fundamental laws like the Ideal Gas Law (pV=nRT) and those governing thermal radiation almost always require absolute temperatures in Kelvin. The conversion is straightforward, simply adding or subtracting a constant value, reflecting the difference in their zero points.
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A gas is cooled from 27 °C to -10 °C. Calculate this temperature change in Kelvin.
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First, find the temperature change in Celsius: .
A sealed container holds 0.50 moles of an ideal gas at a pressure of 1.5 x 10^5 Pa. The volume of the container is 0.012 m³. Calculate the temperature of the gas in degrees Celsius (°C). (The ideal gas constant, R, is 8.31 J K⁻¹ mol⁻¹).
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State the Ideal Gas Law: The relationship between pressure (p), volume (V), number of moles (n), and temperature (T) is given by the ideal gas law: . We need to find the temperature, T.
How it all connects
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Glossary
Key terms for this topic — skim now; the Check step will test them.
- absolute temperature scale
The Kelvin scale is the absolute temperature scale and the SI unit for temperature. It's unique because its zero point, known as absolute zero (0 K), represents the lowest possible energy state for particles, where they theoretically have zero kinetic energy.
- absolute zero
It's unique because its zero point, known as absolute zero (0 K), represents the lowest possible energy state for particles, where they theoretically have zero kinetic energy.
- relative scale
In contrast to Kelvin, the Celsius scale (°C) is a relative scale, based on fixed points related to pure water. It sets 0°C as the melting point of ice and 100°C as the boiling point of water, both at standard atmospheric pressure.
- Kelvin scale
Kelvin (K)
- Absolute scale
It is independent of any substance's specific properties and starts from absolute zero, where particles theoretically have zero kinetic energy.
- Celsius scale
The melting point of pure ice (0°C) and the boiling point of pure water (100°C), both at standard atmospheric pressure.
- ΔK = Δ°C
A change of 1 Kelvin is exactly equal to a change of 1 degree Celsius (ΔK = Δ°C).
- Thermometry
Electrical resistance, volume of a liquid, pressure of a gas, or generated voltage (e.g., in a thermocouple).
- At absolute zero
Particles possess their lowest possible energy state, theoretically having zero kinetic energy.
Quick check
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Teach it back
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Teach it back
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Revision flashcards
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Key takeaways
Review these before you close the topic — retrieval beats re-reading.
14.2 Temperature scales.
A thermometer is any device that is used to measure temperature.
There are many types of thermometer e.g. liquid-in-glass. thermocouple, bimetal thermocouple, etc.
You will need to be able to give an example for each of the above types and explain how it works.
The Kelvin scale is also called the thermo dynamic scale.
Absolute zero is defined as the temperature at which atoms and molecules in all substances have zero kinetic and potential energy.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
Explain how Fig. 2.2 shows that platinum is a suitable metal for use in a resistance thermometer.
Extra simulations & links
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Frequently asked
Checkpoint
One marked question is worth ten re-reads — close the loop before you move on.
Reading it isn’t knowing it — prove it.
Before you move on: do 9702/41 · Q2(b)(i) on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.
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