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Heat

Heat. By Neil Bronks. Expansion. 400 Kelvin (127 0 C). Atoms vibrate more at higher temperature. 200 Kelvin (-73 0 C). Zero Kelvin (-273 0 C). Expansion. This makes objects take up more volume. 400 Kelvin. 200 Kelvin. Zero Kelvin. Ball and ring. Proves solids expand when heated.

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Heat

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  1. Heat By Neil Bronks

  2. Expansion 400 Kelvin (1270C) • Atoms vibrate more at higher temperature 200 Kelvin (-730C) Zero Kelvin (-2730C)

  3. Expansion • This makes objects take up more volume 400 Kelvin 200 Kelvin Zero Kelvin

  4. Ball and ring Proves solids expand when heated

  5. Solids • Expansion can damage railway lines

  6. Expansion Joints on Bridges

  7. Bi-Metallic Strip • The bottom metal expands more than the top strip. • It bends! • Used to control Gas Oven

  8. Bi-Metallic Strip • The bottom metal expands more than the top strip. • It bends! • Used to control Gas Oven

  9. Liquids • Use to measure temperature as liquid expands up a tube

  10. Gas • Expands a lot with a small temperature rise

  11. Heat Transfer • Convection • Hot air • rising • carrying • the • heat up • with it. Conduction -Transfer by vibrations Radiation -Transfer by Electro-magnetic wave

  12. Conduction In a solid every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the vibration travels through the solid. Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance.

  13. Internet Conduction

  14. Practical Conduction • A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids • It is also why stone and metals appear cold. They are just good conductors. Chilly

  15. Test Tube of water Metal Gauze ICE HEAT Water as a Poor Conductor The ice does not melt as the water is a terrible conductor and convection only works up.

  16. Convection Most houses have radiators to heat their rooms. This is a bad name for them - as they give off heat mainly by convection! The air expands and is less dense so it rises It then cools and falls CONVECTION CURRENT

  17. Internet ex

  18. Example of convection currentSea Breezes Day – On Shore HOT LAND WARM SEA

  19. Sea Breeze Night Night – Off Shore COLD LAND WARM SEA

  20. Ventilation with convection

  21. Mine Ventilation Demo

  22. Radiation • The transfer of heat in the form of an electro-magnetic wave. • Only form of heat that can travel through a vacuum

  23. A silver or white body are good at holding and reflecting heat. Black bodies are good at radiating and absorbing heat.

  24. Insulation • Vacuum stops heat loss by conduction and convection • Silver prevents heat loss by radiation

  25. Latent Heat • When something boils it takes in heat to change state • Its temperature does not rise. • Latent heat just changes state

  26. Melting point Boiling point Heating a solid Temperature Time

  27. Boiling point Heat raises temperature Boiling Melting point Liquid Melting Latent Heat Only Solid Heating a solid Temperature Gas Time

  28. Sweat • Our sweat evaporates and takes heat from our bodies • Liquid sweat takes heat from skin as it turns to vapour

  29. Uses of Latent Heat • Perspiration-Liquid evaporates to gas takes heat from our skin • Boiling or Melting matter • Refrigeration-liquid boils to take heat from food • Heat Pumps- reverse of refrigerator • Latent heat is heat that changes state

  30. The Fridge

  31. Liquid boils and takes in Latent Heat from the food Gas turns back into a liquid giving out heat The Refrigerator Liquid Gas Compressor

  32. Summary

  33. Summary • Water a poor conductor • Black good emitter and absorber • Silver and white a good reflector and insulator • Latent Heat is the heat lost or gained as a material changes state – e.g. sweat • Expansion is the volume change in solids liquids and gases.

  34. H/W • P336 1,2,5,7,8,9,10,11,12,13

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