In simple terms
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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
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Key formulas
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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
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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.
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Glossary
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Revision flashcards
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What is the SI unit for absolute temperature?
Kelvin (K)
Key takeaways
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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
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