The document discusses thermal radiation and how heat is radiated from objects in the form of infrared waves. Dark or black colored objects are good radiators of heat as they absorb infrared radiation well, while light colors like white are good for reflecting heat. An example given is of a man wearing a white suit to reflect sunlight during a space walk.

1. Thermal radiation Target To know how radiation of heat takes place Wednesday 25 November 2009

2. What is this? Shower – red where water is hottest

3. What is this? Pylons – red where they are hottest

4. What is this? Car – red where wheels are hottest due to braking

5. What is this? Car park – white where there are warm objects – people and cars

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11. Thinking task Look at the picture of a man running away from an exploding volcano. Why is he dressed in the white suit?

12. What is radiation of heat? Heat is radiated by any hot object as INFRA RED waves – they pass through air or a vacuum – they cannot be seen

13. Good radiators of heat Black (or dark) coloured objects radiate heat best. A motorcycle with the black engine cools faster than one with a silver engine!

14. Good absorbers of radiation heat Black (or dark) colours also absorb radiation heat best. So dark surfaced objects quickly become warmer.

15. Questions 1. What do light rays and infra red rays have in common? 2. Why is this boy feeling so hot? 3. Why is the man wearing a white suit for the space walk? Light rays and infra red rays travel at the speed of light. Wearing black clothes make a person feel hot because black absorbs infra red waves very well. White suits reflect heat so they reflect sunlight during a walk in space.

16. More questions 4. What colour should the inside of a cooler box be made? Explain your answer. 5. Why does the tar melt on the road on a summers day? 6. Why do people living in hot countries often paint their houses white? 7 Solar panels are usually black in colour – what is the reason for this? Cooler boxes should be white or silver to stop heat being absorbed. Tar on the road melt on a hot summer because black absorbs heat very well. Houses in hot countries are painted white to reflect light and heat waves and keep the house cool. Solar panels are painted black to absorb light and heat wave so they warm the water in the pipes.