All objects emit infrared radiation, with hotter objects emitting more. Infrared radiation can transfer heat through a vacuum in space where there are no particles for conduction or convection. The police use infrared cameras to detect suspects at night since people emit infrared radiation even when not visible with the naked eye. Reflective surfaces like white clothing and buildings reflect infrared radiation, keeping surfaces and people cooler.

1. 5.6 Using Radiation06 January 2011What is conduction?What is convection?How are they different?

2. AimsExplain that all objects emit infrared radiation and that hotter ones emit more. [Level 4]Explain how the surface of an object affects how radiation interacts with it. [Level 5]Describe how hot objects transfer heat through a vacuum. [Level 7]

3. Key wordsEvaporationInfra-redRadiationReflect

4. Energy through spaceThere are no particles in space.Heat cannot travel by conduction or convection from the earth to the SunThere has to be a method to transfer heat without particles

5. RadiationEnergy can indeed go through nothing, it’s called radiationAll hot objects emit infra-red radiation, which we feel as heatThe police use cameras to detect infra-red radiation to find suspects

10. QuestionExplain why thermal transfer cannot happen in space by conduction of convection

11. AnswerConduction only occurs in solid, convection only occurs in fluids. There are no particles in space so therefore no liquids, solids or gases.

12. QuestionWhy do the police use infra-red to track people at night?

13. AnswerNo visible light at night which our eyes require. Still lots of infra-red emitted by people so use a detector to find IR. Therefore we can detect people.

14. Reflecting radiationRadiation reflects off shiny or white materialsIn hot countries many buildings are white and summer sports tend to wear white clothes tooThis keeps things coolerIf the radiation is reflected back to the person it will keep them warm

20. QuestionWhy will melting the north and south poles lead to more global warming (think about colour!)

22. How do your clothes dry? Evaporation

23. EvaporationWhy air blows against the wet clothes, some energy transfers from the air to the water.If a water particles get enough energy it will become a gas and fly away.Your body cools itself in exactly the same way!

24. 5.6 Using radiationQuestions(Level 4)Why do solar power stations use a lot of mirrors?What is the everyday word for thermal radiation? If you wanted to keep your house warm on a cold day, what colour should your walls be? Explain your answer. When it rains, the ground gets wet. Explain why it becomes dry again afterwards.(Level 5)(Level 6)(Level 6)1 of 2

25. 5.6 Using radiationQuestions(Level 6)Astronauts’ suits are made of a light, reflective material. What would happen if they were made of a black material?When you sweat, evaporation helps you to cool down. Explain why you cool down when you sweat.A rattlesnake’s eyes can detect infrared radiation. It often hunts mice. What time of day do you think rattlesnakes prefer to hunt and why? Explain your answer using as much science as possible. (Level 6)(Level 7)2 of 2