2. Heat By Neil Bronks By Neil Bronks

3. Expansion  Atoms vibrate more at higher temperature Zero Kelvin (-273 0 C) 200 Kelvin (-73 0 C) 400 Kelvin (127 0 C)

4. Expansion  This makes objects take up more volume Zero Kelvin 200 Kelvin 400 Kelvin

5. Ball and ring Proves solids expand when heated

6. Solids  Expansion can damage railway lines

7. Expansion Joints on Bridges

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

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

10. Liquids  Use to measure temperature as liquid expands up a tube

11. Liquid expansion demo

12. Gas  Expands a lot with a small temperature rise

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

14. 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.

15. 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.  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

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

17. ConvectionConvection 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

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

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

20. Ventilation with convection

21. Mine Ventilation Demo

22. RadiationRadiation  The transfer of heat in the form of an electro-magnetic wave.  Only form of heat that can travel through a vacuum  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  Vacuum stops heat loss by conduction and convection  Silver prevents heat loss by radiation

25. The Fridge

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

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

28. Heating a solid Temperature Time Melting point Boiling point

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

31. 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  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

32. Summary ConductionConvectionRadiation Particles vibrate and transfer their heat to the next particle Particles move and bring their heat with them Heat transferred without the need of a medium (waves)

33. Summary

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