Temperature

Objectives

Lesson outcomes

Explain thermal energy transfer in terms of temperature difference and thermal equilibrium.
Describe how temperature-dependent physical properties can be used in thermometers.
Convert temperatures between degrees Celsius and kelvin using T / K = theta / degrees C + 273.15.
Explain why thermodynamic temperature has an absolute zero and does not depend on a particular substance.

Syllabus

CIE 9702 syllabus points

6 linked

14.1.1 understand that (thermal) energy is transferred from a region of higher temperature to a region of lower temperature
14.1.2 understand that regions of equal temperature are in thermal equilibrium
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 T / K = θ / °C + 273.15
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

Lesson Notes

Student guidance and lesson notes

Overview

This lesson sets up the temperature ideas needed for A2 thermal physics. Temperature tells you the direction of thermal energy transfer and lets you decide when two regions are in thermal equilibrium. You also connect everyday Celsius readings to the thermodynamic temperature scale used in gas equations.

What You Need to Know

Thermal energy is transferred from a region at higher temperature to a region at lower temperature.
Regions at the same temperature are in thermal equilibrium, so there is no net thermal energy transfer between them.
A thermometer uses a physical property that changes with temperature, such as liquid density, gas volume at constant pressure, metal resistance, or thermocouple e.m.f.
Thermodynamic temperature is measured in kelvin and does not depend on the behaviour of one particular material.
The conversion is T / K = theta / degrees C + 273.15, and absolute zero is 0 K.

How to Work Through It

Start by comparing pairs of objects and predicting the direction of thermal energy transfer.
Decide whether each pair has reached thermal equilibrium.
Link common thermometer properties to the temperature range and sensitivity they can measure.
Practise Celsius-kelvin conversions before using kelvin in later gas calculations.

Check Your Understanding

Why does thermal energy transfer stop when two objects are at the same temperature?
Which physical property could be used in a thermometer for a high-temperature measurement?
What is 25 degrees C in kelvin, and why must gas equations use kelvin?

Common Mistakes

Treating temperature as the same thing as internal energy or thermal energy.
Using degrees Celsius directly in A2 gas equations.
Thinking absolute zero is just a convenient low temperature rather than the lower limit of the thermodynamic temperature scale.

Next Steps

Keep thermal equilibrium and kelvin conversions secure before using thermal energy equations.
Bring the idea of temperature change into the next lesson on specific heat capacity and latent heat.