Transfer of Thermal Energy Pt 2 - Radiation & Practice | Year 11

Objectives

Lesson outcomes

Explain thermal radiation as infrared radiation that does not need a medium.
Describe how colour and texture affect emission, absorption, and reflection of infrared radiation.
Explain how surface temperature and area affect the rate of radiation.
Apply conduction, convection, and radiation together in everyday thermal examples.

Syllabus

CIE 0625 syllabus points

11 linked

2.3.3.1 Know that thermal radiation is infrared radiation and that all objects emit this radiation
2.3.3.2 Know that thermal energy transfer by thermal radiation does not require a medium
2.3.3.3 Describe the effect of surface colour (black or white) and texture (dull or shiny) on the emission, absorption and reflection of infrared radiation
2.3.3.4 Know that for an object to be at a constant temperature it needs to transfer energy away from the object at the same rate that it receives energy
2.3.3.5 Know what happens to an object if the rate at which it receives energy is less or more than the rate at which it transfers energy away from the object
2.3.3.6 Know how the temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted from the Earth’s surface
2.3.3.7 Describe experiments to distinguish between good and bad emitters of infrared radiation
2.3.3.8 Describe experiments to distinguish between good and bad absorbers of infrared radiation
2.3.3.9 Describe how the rate of emission of radiation depends on the surface temperature and surface area of an object
2.3.4.1 Explain some of the basic everyday applications and consequences of conduction, convection and radiation, including: (a) heating objects such as kitchen pans (b) heating a room by convection
2.3.4.2 Explain some of the complex applications and consequences of conduction, convection and radiation where more than one type of thermal energy transfer is significant, including: (a) a fire burning wood or coal (b) a radiator in a car

Lesson Notes

Student guidance and lesson notes

Overview

This lesson completes the thermal transfer topic by adding radiation and then forcing you to compare all three methods together. The aim is to recognise not just what radiation is, but when several processes are happening at once in the same real situation.

What You Need to Know

Thermal radiation is infrared radiation, and all objects emit it.
Radiation does not need a medium, so it can transfer energy through empty space.
Dull black surfaces are good emitters and good absorbers of infrared radiation.
Shiny light-coloured surfaces are poor emitters and absorbers and good reflectors.
A hotter object and an object with a larger surface area emit radiation faster.
An object stays at constant temperature when the rate it receives energy equals the rate it loses energy.
Everyday systems often involve more than one transfer process at the same time, such as a fire or a car radiator.

How to Work Through It

Start with the difference between transfer that needs a medium and transfer that does not.
Compare surfaces and predict which will emit, absorb, or reflect infrared best.
Work through a few energy-balance situations where an object warms up, cools down, or stays at constant temperature.
Finish with mixed practice questions that combine conduction, convection, and radiation in real examples.

Check Your Understanding

Why can thermal radiation travel through a vacuum?
Which surface is the best emitter of infrared radiation?
What must be true for an object to stay at a constant temperature?
In a kitchen pan on a hob, which transfer methods are involved?

Common Mistakes

Treating radiation as if it needs particles to carry it. Thermal radiation is electromagnetic.
Mixing up good absorbers and good reflectors. A good absorber is not a good reflector.
Naming only one transfer method in a situation where several are active.

Next Steps

Use the practice questions to rehearse comparison answers, not just definitions.
Pull together the whole topic before the revision lesson so particle ideas, equations, and transfer processes still connect.

Lesson Resources

Materials for this lesson

Use these videos, slide decks, documents, or links to work through the lesson.

Slides for the lesson

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Practice PPQs