Keyword: Absorber Emitter Reflector Surfaces & Radiation Keyword: Absorber Emitter Reflector
Learning Objectives: Identify and explain • Matt black surfaces are the best emitters and absorbers of thermal radiation. • Silver surfaces are the worst emitters and absorbers of thermal radiation. I will be successful in this lesson if I can: Use the connectives triangle with literate accuracy. Use the keywords to ‘bingo’ your work throughout the lesson. Work together as a team with all members effectively contributing in order to solve a problem (Team work, Effective Participator, Interpersonal) • Describe which surfaces are the best emitters of thermal radiation (Grade C). • Describe which surfaces are the best absorbers of radiation (Grade C). • Explain how the choice of a surface colour can affect the rate of temperature change of an object (Grade A).
STARTER What colour is a polar bear? WHY?
When you go out in the ‘sun’ today, your in for a big surprise…. Use this description to write a definition for each of the keywords Use your keywords (bingo) to explain what happens to each women
Leslie’s Cube? and his cube this leslie NO not that leslie To demonstrate that two surfaces at the same temperature can give off different amounts of thermal radiation. An infra-red sensor can be used to detect levels of IR radiation from the cube. • The difference is easily felt by placing the back of the hand a few centimetres from the surfaces, but care must be taken that the students do not actually touch the surface. and his cube this leslie NO not that leslie
How can we test different surfaces for their emission of thermal radiation? Equipment and materials required Kettles two beakers, two thermometers, aluminium foil and black card, elastic bands (to hold the card on), stopclock, a measuring cylinder. Details It is essential to use ‘lids’ on the containers to reduce evaporation; that thermometers can be poked through to keep a good seal. Higher starting temperatures give greater temperature drops in reasonable times but be extra careful with hot water. In your books; Heading; Investigation on emission What are you trying to find out? Clarify your independent & dependant variable Identify what variables will be controlled Explain how & why they will be controlled Draw up a table …then do the experiment…. In your books; Decide which graph to draw from your results Draw your graph Identify what you found out be specific by your independent and dependant variable and referring to actual results
Black surfaces (dark, matt colours) are better emitters than white (light, shiny) surfaces. Explain this by drawing coloured cars
PLENARY What colour cup would be best to keep orange juice cold on a hot day? Explain your answer
Learning Objectives: Identify and explain • Matt black surfaces are the best emitters and absorbers of thermal radiation. • Silver surfaces are the worst emitters and absorbers of thermal radiation. I will be successful in this lesson if I can: Use the connectives triangle with literate accuracy. Use the keywords to ‘bingo’ your work throughout the lesson. Work together as a team with all members effectively contributing in order to solve a problem (Team work, Effective Participator, Interpersonal) • Describe which surfaces are the best emitters of thermal radiation (Grade C). • Describe which surfaces are the best absorbers of radiation (Grade C). • Explain how the choice of a surface colour can affect the rate of temperature change of an object (Grade A).
Summary notes Dark, matt surfaces are good absorbers of radiation. An object painted dull black & left in the sun will become hotter than the same object painted shiny white. Dark, matt surfaces are also good emitters of radiation. So an object that is painted dull black will lose heat and cool down quicker than the same object painted shiny white. Don’t be fooled by most central heating radiators that are covered in glossy white paint. The best radiators of heat are dark, matt surfaces. Remember that an object that is warmer than the surroundings will lose heat and cool down. An object that is cooler than the surroundings will gain heat energy and warm up. Exam questions will centre around applications of absorption & emission so make sure you understand the difference.
Check your understanding Which surfaces are the best emitters of ehat radiation? Which surfaces are the best absorbers of heat radiation? Why are the pipes on the back of a fridge usually painted black? CLICK AGAIN FOR THE ANSWERS ANSWERS: The best emitters of heat radiation are dark, matt surfaces. The best absorbers of heat radiation are dark, matt surfaces. To maximise the amount of heat they radiate.