Sign In Sign Up
← Back to Physics
AS & A-Level Physics 14 — Temperature and Thermal Processes

AS & A-Level Physics 14 — Temperature and Thermal Processes

Public

Independent Deckloop revision aligned with the Cambridge International AS & A Level Physics (9702) syllabus, 2025–2027. Not affiliated with or endorsed by Cambridge International Education. Chapter 14 of 26: Temperature and thermal processes. Concepts, worked applications and misconception checks.

Physics EN A-Level
48 cards
Study this deck on Deckloop

Preview Cards

A sample of cards from this deck.

Example Explainer

A sample of the AI explainer you can generate for cards in this deck.

Thermometric Properties for Temperature Measurement

To measure temperature, we rely on physical properties of substances that change predictably with temperature. These are known as thermometric properties. Examples include the expansion of liquids (like mercury or alcohol in a glass thermometer), the change in volume or pressure of a gas (as in a constant-volume gas thermometer), the variation in electrical resistance of a metal (used in resistance thermometers), and the electromotive force (e.m.f.) generated at the junction of two dissimilar metals (as in a thermocouple). For most thermometric properties, the relationship with temperature is not perfectly linear, so a calibration curve is often needed to accurately convert the measured property into a temperature reading.

Key points

  • Thermometric properties are physical properties that vary predictably with temperature.
  • Examples include liquid expansion, gas volume/pressure, metal resistance, and thermocouple e.m.f.
  • Liquid-in-glass thermometers use thermal expansion of the liquid.
  • Thermocouples generate an e.m.f. dependent on junction temperature.
  • Calibration curves are often necessary due to non-linear relationships.

Worked example

Question

Explain how the electrical resistance of a metal wire can be used to measure temperature, and state one advantage of this method over a liquid-in-glass thermometer.

Solution

1. Identify the thermometric property: Electrical resistance of a metal.
2. Explain the mechanism: As temperature increases, the metal ions vibrate more vigorously, increasing the frequency of collisions with conduction electrons. This impedes electron flow, increasing resistance.
3. Method of measurement: Measure the resistance, then use a pre-calibrated relationship (often a calibration curve) to determine the temperature.
4. State an advantage: Resistance thermometers can be very accurate, have a wide temperature range, and can respond quickly to temperature changes, unlike liquid-in-glass thermometers which have a limited range and slower response.

The electrical resistance of a metal wire increases as its temperature rises. This is because the atoms in the metal lattice vibrate with greater amplitude at higher temperatures, leading to more frequent collisions with the free electrons that carry the current, thus hindering their flow and increasing resistance. By measuring this resistance and using a known calibration, the temperature can be determined. An advantage of using a resistance thermometer over a liquid-in-glass thermometer is its ability to measure a much wider range of temperatures, from very low to very high, and its faster response time to temperature changes.

Common pitfalls

  • Assuming all thermometric properties vary linearly: Most do not, which is why different empirical scales don't perfectly agree and calibration is crucial.
  • Not understanding the underlying physics: Simply listing properties isn't enough; understanding why they change (e.g., increased molecular motion, increased electron scattering) is important.

Prerequisites

  • Requires a foundational understanding of temperature and thermal concepts.
Further resources