All bodies (objects) of all temperatures emit and absorb infrared radiation. Hotter bodies emit more IR in a set time.
The range of wavelengths emitted, and their intensities, depend on an object’s temperature.
Good absorbers (e.g. dark and dull surfaces) are also good emitters. Shiny metal surfaces are poor absorbers/emitters.

Keywords

Infrared radiation - Infrared radiation means electromagnetic waves with frequencies in a range just lower than for red light.
Emit - To emit infrared radiation is to give out infrared radiation.
Temperature - The temperature of an object measures how hot or cold it is.
Leslie cube - A Leslie cube is a hollow metal cube that can be filled with hot water. Each side has a different colour and finish so emits different intensities of infrared radiation.

Common misconception

White surfaces are always poor absorbers of visible light so they must also always be poor absorbers and emitters of infrared.

White paint is a good absorber and emitter of IR. Colour is not always a good guide to effectiveness at emitting/absorbing IR, except for dark+dull surfaces usually being good emitters/absorbers and shiny metal surfaces being poor emitters/absorbers.

The practical included in the first learning cycle of this lesson is a method required by the current Edexcel GCSE science specifications. Teachers of other exam boards could consider whether to adapt the lesson to include this practical or not, to allow a greater focus on other parts of the lesson.

Teacher tip

Equipment

Detailed in the Additional Materials (teacher and technician notes) for this lesson.

Content guidance

Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

Which of the following is not a type of electromagnetic radiation?

infrared

light

Correct answer: sound

X-rays

Q2.

Which of the following types of electromagnetic radiation are emitted by a hot light bulb?

Correct answer: infrared

microwaves

Correct answer: light

gamma radiation

Q3.

Surfaces can absorb radiation. Which of the following words or phrases is closest in meaning to the word absorb?

attract

fill up

Correct answer: soak up

suck in

Q4.

Which of the following statements about infrared radiation are correct?

Correct answer: It is invisible to human eyes.

It can be absorbed but not emitted.

It can be emitted but not absorbed.

It has higher frequencies than light but lower frequencies than microwaves.

Correct answer: It has lower frequencies than light but higher frequencies than microwaves.

Q5.

Match up the following key terms about waves with their definitions.

Correct Answer:amplitude,The maximum displacement of a wave from the rest position.

The maximum displacement of a wave from the rest position.

Correct Answer:frequency,The number of wavelengths passing a point each second.

The number of wavelengths passing a point each second.

Correct Answer:oscillation,A regular, repeating forwards–and–backwards movement.

A regular, repeating forwards–and–backwards movement.

Correct Answer:wavelength,Distance between two equivalent points on neighbouring wavelengths.

Distance between two equivalent points on neighbouring wavelengths.

Q6.

Which of the following statements about thermal conduction are correct?

Thermal conduction can happen in a vacuum.

Correct answer: Metals are particularly good thermal conductors.

Thermal conduction in a room starts when warmer air rises.

Correct answer: Thermal conduction happens when energy is transferred by vibrating particles.

Exit quiz

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6 Questions

Q1.

A pupil has test tubes of hot water covered in different colours of paper. He investigates whether colour affects the rate of infrared emission. Match each variable with its type in this experiment.

Correct Answer:starting temperature of the water,control variable

control variable

Correct Answer:temperature drop in a set time interval,dependent variable

dependent variable

Correct Answer:colour of paper,independent variable

independent variable

Q2.

A pupil has beakers of hot water covered in different colour paper to investigate how colour affects temperature drop caused by infrared energy transfer. Match the parts of her method with the reason.

Correct Answer:same thickness of paper on beakers,This variable affects the rate of energy transfer.

This variable affects the rate of energy transfer.

Correct Answer:same mass of water in beakers,This variable affects temperature change when energy is transferred.

This variable affects temperature change when energy is transferred.

Correct Answer:lids on beakers,This reduces energy transfer by evaporation.

This reduces energy transfer by evaporation.

Q3.

An infrared thermometer may show different temperature readings for two objects that are at the same temperature. Which of the following is a possible explanation?

One object is heavier than the other.

Correct answer: One object is shiny and the other is dull.

The objects are also losing heat by conduction.

Q4.

Match the following types of surface to the description of how well it absorbs infrared radiation.

Correct Answer:dull and white,sometimes a good and sometimes a poor absorber

sometimes a good and sometimes a poor absorber

Correct Answer:shiny metallic,usually a poor absorber

usually a poor absorber

Correct Answer:dull and dark,usually a good absorber

usually a good absorber

Q5.

Which of the following statements about the absorption and emission of infrared (IR) radiation are correct?

Correct answer: If a surface is a good absorber of IR radiation, then it is a good emitter.

If a surface is a good absorber of IR radiation, then it is a poor emitter.

If a surface is a poor absorber of IR radiation, then it is a good emitter.

Correct answer: If a surface is a poor absorber of IR radiation, then it is a poor emitter.

Q6.

A metal rod is heated until it glows red. Which of the following statements describes what happens if the rod gets hotter?

Correct answer: The radiation emitted by the rod transfers more energy per second.

The wavelength carrying the most energy per second becomes a longer wavelength.

Correct answer: The range of emitted wavelengths increases to include shorter wavelengths.

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