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Warm-up

Warm-up. Why are frying-pans and woks usually made of metals but their handles are made of plastic?. Introduction. How is energy transferred from the cooker to the pan and then to the food?. Energy transfer by conduction. Energy is transferred by conduction. from the cooker,.

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Warm-up

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  1. Warm-up Why are frying-pans and woks usuallymade of metals but their handles are made of plastic?

  2. Introduction How is energy transferred from the cooker to the pan and then to the food?

  3. Energy transfer by conduction Energy is transferred by conduction from the cooker, through the pan, to the food.

  4. Conduction (video) Studying the heat transferred along a metal rod insulating board copper rod wax What happens to these drawing pins? drawing pins

  5. Conduction (video) What kind of rod conducts heat? Feel the ends of the rods tofind out which rod feels hot first. wood iron glass copper very hot water

  6. Conduction (video) What kind of rod conducts heatfastest? Heatthe ends of the metal rods and notewhich drawing pin at the other end falls first. aluminium copper iron drawing pins

  7. Conduction (video) Does water conduct heat? boiling tube Gently heat the top part of the water & find out if the ice melts. wire gauze water ice

  8. Conduction (video) Does air conduct heat? thermometer Leave the cardboard for a while & then take the temperature readings. heater cardboard tube

  9. Conduction (video) Does air conduct heat? Leave the cardboard for a while & then take the temperature readings.

  10. Energy transfer by conduction In conduction, heat (energy) is transferred from the hot part to the cold part. Materials conduct heat at different rates. Metals (e.g. copper and iron) are good conductorsof heat. Non-metals (e.g. wood, water and air) are poor conductors (or good insulators).

  11. Energy transfer by conduction In conduction, heat is transferred from the hot part to the cold part along an object. Conduction is efficient in conductors but not in insulators.

  12. Energy transfer by conduction Does the orientation of the rod matter?

  13. Does the orientation of the rod matter? Phoebe heats two metal rods as shown. Which will be heated up first? Why? Bothof them are heated up at the same rate. Energy transferred from the hot end to the cold end by conduction is not affected by the orientation of the rod.

  14. Conduction and particle motion particles at cold end vibrate less In kinetic theory, particles in a solid are closely packed, they vibrate to & fro but can't change positions. particles at hot end vibrate a lot

  15. Conduction and particle motion particles at cold end vibrate less The fast vibrating particlesbump into the slower neighbouring particles & make them vibrate more rapidly  energy is transferred particles at hot end vibrate a lot (from one particle to the next & from hot to cold end of rod)

  16. Conduction and particle motion (simulation)

  17. Examples of conduction How to keep warm? A cotton jacket keeps warm by trapping air next to the body.

  18. Examples of conduction How to keep warm? Polar bears keep warm by trapping air in the fur.

  19. Examples of conduction (video) How to keep warm? Birds keep warm by trapping air in their feathers.

  20. Examples of conduction Hot or cold? Under the same condition, a metal block feels colder than a wooden block even the 2 objects are at the same temperature. metal easily conducts energy away from your hand   you feel cold

  21. In conduction, heat is transferred... In conduction, heat is transferred in which of the following direction? A From high-temperature area to low-temperaturearea. B From low-temperature area to high-temperature area. C The direction of heat transferred is different inmetals and non-metals.

  22. Which of the following can explain why a tile floor feels colder than a wooden floor? A The temperature of the tile floor is lower. B Tile is a better conductor of heat than wood. C Wood is a better conductor of heat than tile. D Tile is smoother than wood.

  23. Frying-pans are made of... Frying-pans are made of metals because they are good _________ of heat, while handles offrying-pans are made of plastic because they are good_________ of heat. conductors insulators

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