678831922-Cambridge-Lower-Secondary-Science-Year-9-Science-Unit-3-5-Ways-of-transferring-thermal-energy-5-April-2023.pptx

Heat transfer mode like conduction convection and radiation

1. Ways of transferring thermal energy Year 9 Science Unit 3.5 (5 Apr, 2023)

2. So in this lesson, we will cover…

3. Conduction

4. Conduction

5. Demonstrating conduction: Metals

6. Demonstrating conduction: Water

7. In general, how does heat conduction work? View in presentation mode The particles near the fire receive heat energy and start vibrating more. They collide more strongly with their neighbours, transferring some energy to them.

8. Convection

9. Demonstrating convection

10. How convection works View in presentation mode

11. How convection works As the food colouring syrup near the fire gets heated, it expands, becoming less dense The denser cold water sinks, displacing the warmer syrup, making it rise up As the cold water gets close to the fire, it in turn gets heated up, gets less dense, and so rises This causes circulation in the liquid ( convection current ) This process keeps repeating

12. Example: Convection in everyday life – Air conditioners and heaters Air conditioners are fixed near the ceiling . Why? What happens if we fix them near the floor? Heaters are fixed near the floor . Why? What happens if we fix them near the ceiling?

13. Conduction vs convection in liquids Liquids can transfer heat through conduction and convection (though convection is faster in liquids) In conduction, the particles of the liquid don’t move all over the liquid; only the energy does (because of particles bumping into nearby neighbours) But in convection, the particles of the liquid move all over the liquid, and so does the energy (carried everywhere by the particles)

14. Radiation

15. What is infrared (IR) radiation? Infrared Ultraviolet We know the colours of the rainbow… these are the different colours of light that we can see (visible light) Infrared (IR) radiation is just another “colour” of light… one that we can’t see So, it’s similar to ultraviolet (UV) light… also a “colour” of light that we can’t see IR light is the invisible “colour” of light that carries heat energy with it

16. Demonstrating heat (IR) radiation This is an infrared camera view of a warm human body radiating heat out into cooler surroundings Just like light bulbs shine / radiate visible light, warm-blooded creatures radiate / “shine” heat (IR light)

17. Infrared (IR / heat) radiation View in presentation mode

18. How does heat (IR) radiation work?

19. Factors affecting heat transfer

20. Good absorbers, good emitters Good absorbers of heat (IR radiation) are also good emitters, and good emitters are also good absorbers Dark coloured, dull surfaces are good heat (IR) absorbers / emitters Light coloured, shiny surfaces are bad heat (IR) absorbers / emitters Light coloured, shiny surfaces are good heat (IR) reflectors

21. Factors affecting rate of heat transfer Colour (only affects radiation): Darker colours absorb / emit heat (IR) faster, lighter colours do them slower Type of surface (only affects radiation): Dull surfaces absorb / emit heat (IR) faster, shinier surfaces do them slower (but they reflect heat well) Surface area (affects radiation, conduction, and convection): Surfaces with larger area transfer heat faster, smaller areas transfer heat slower Temperature difference (affects radiation, conduction, and convection): The larger the temperature difference between heat source and heat sink, the faster the heat transfer The smaller the temperature difference, the slower the transfer

22. Happy Science- ing ; stay curious!