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HEAT ENERGY AND ITS TRANSFER

HEAT ENERGY AND ITS TRANSFER. HEAT TRANSFER BY RADIATION. Learning Points. 1. State that heat is transferred in straight lines in all directions by radiation. 2. State that heat rays are also known as infra-red rays. 3. Give examples of the uses of infra-red radiation.

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HEAT ENERGY AND ITS TRANSFER

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  1. HEAT ENERGY AND ITS TRANSFER

  2. HEAT TRANSFER BY RADIATION

  3. Learning Points 1. State that heat is transferred in straight lines in all directions by radiation. 2. State that heat rays are also known as infra-red rays. 3. Give examples of the uses of infra-red radiation.

  4. Heater Infrared Radiation • Heat energy waves (or rays) are known as • Infrared Radiation. • Infrared Radiation waves will travel out from • a hot source in all directions.

  5. Infrared Radiation • Heat energy from the sun travels to earth by • radiation. • Since the space between the sun and the earth • is a vacuum (no particles present), the heat • cannot travel by conduction or convection.

  6. Infrared Radiation pictures • Special Infrared cameras can be used to • show the Infrared radiation given off by • different objects. gosublogger.com

  7. Infrared Radiation pictures • This is a infrared image of a child’s hand holding a lizard. • Lizards are reptiles and are cold blooded. • Notice how the child`s hand is warm compared to the lizard.

  8. Infrared Radiation pictures • This is an infrared image of a person. • What area is the hottest? • What do you think it is?

  9. Infrared Radiation pictures • This is an infrared image of two coffee cups containing very hot drinks.

  10. Infrared Radiation pictures • This is a infrared image of a dear in the dark. • Since infrared cameras detect heat radiation they can see the heat from warm blooded animals in the dark.

  11. Infrared Radiation pictures • This infrared medical scan shows an injured and healthy leg. • The bright white region shows the location of the injury, which is warmer due to the increased blood flow to the injured area.

  12. Infrared Radiation pictures • This is a infrared image of footprints. • As this person walks away barefoot the heat left behind her feet stills glows on the ground.

  13. Infrared Radiation pictures • This is an infrared image of a cat. • The yellow areas are the warmest and the purple areas are cool.

  14. Infrared Radiation pictures • This is a infrared image of a tyre that has been heated by friction with the road. • Notice how the area of the tyre that touches the road glows much more brightly when you look through the infrared camera.

  15. Infrared Radiation pictures • This is a infrared image of a zebra. • Notice how the stripes appear on the infrared. • Do you think these are the black or white stripes?

  16. Infrared Radiation pictures • This is an infrared image of a heating element. • Even after the stove is turned off, this heating element will glow brightly in the infrared until it reaches room temperature.

  17. Infrared Radiation pictures

  18. Infrared Radiation pictures • This is a infrared map of global sea surface temperatures. • Infrared satellites are used to measure and track changing ocean surface temperatures to help predict weather patterns.

  19. Radiation Absorbers and Emitters • Different surfaces will absorb different amounts of • infrared radiation. -Dull, black surfaces are good absorbers of radiation. -Light, shiny surfaces will reflect the radiation.

  20. Vacuum Flask freshpromotions.com.au

  21. Vacuum Flask • A vacuum flask has a double wall of silvered glass with some vacuum between the wall. • The silvered surfaces reflect the infrared radiation from the very hot contents back in to the flask. • The vacuum between the outer and inner walls prevents heat loss through conduction.

  22. Quick Quiz • What direction does radiation travel? • Which will radiate more heat, black or shiny surfaces? • Which will absorb more heat? In all directions in a straight line Black Black

  23. Quick Quiz • What’s the other name for heat radiation? • Give two uses for this radiation. Infra-red Infrared photographs, remote controls, heat seeking missiles, searching for earthquake survivors, chasing criminals, making toast, keeping homes warm…

  24. Radiation • Put 5mls hot water into each test tube • Take the temperature at time ‘0’ • Take the temperature of each test tube every minute for 10 minutes • What results would you expect? Why Glass Black paper Silver foil

  25. Radiation • Thermal energy can travel in waves, a bit like light • Waves do not need particles so: • They travel very fast (300 000km/sec) • They can travel through a vacuum (e.g. Space) • They can be reflected • They can not travel through opaque objects – the energy gets absorbed instead

  26. Visible Spectrum

  27. Radiation – what have we learnt? • Copy and complete the following: The water in the test tube covered in black paper cooled.....this is because... The water in the test tube covered in silver foil cooled....this is because... • Houses in hot countries are often painted white – explain why you think this is. • Polar bears actually have black skin beneath their fur – explain why you think this is.

  28. Heat Transfer-Summary 1. Conduction 2. Convection 3. Radiation.

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