1. 1 3.2 Convection Air conditioners and under-floor heating Convection current Convection and particle motion Examples of convection Check-point 2 ? E

2. 2 3.2 Convection Air conditioners and under-floor heating Look around! Where are the air-conditioners? Why are they usually installed high up on the wall?

3. 3 3.2 Convection Air conditioners and under-floor heating …because the cold air released from air conditioners sinks. It is… Heat is transferred by convection.

4. 4 3.2 Convection 1 Convection in water Put a purple crystal into a beaker of water near the side. Experiment 3b Convection note its movement Video

5. 5 3.2 Convection 2 Convection in air Experiment 3b Convection Light the candle & hold a piece of smoking paper on the other side of the cardboard. note smoke's movement Video

6. 6 3.2 Convection 1Convection current water expands, rises & is replaced by cold water from above. Experiment 3b shows: When the water is heated at the bottom,

7. 7 3.2 Convection 1Convection current The flow of water is called convection current. This method of heat transfer is called convection.

8. 8 3.2 Convection 1Convection current Similarly, when air is heated, air expands, rises & is replaced by cold air from above.  convection current

9. 9 3.2 Convection 1 Convection current Heat can be transferred in a fluid (liquid/gas) by convection, Such movement of fluid is called convection current. in which the heated fluid expands, rises and is replaced by the surrounding cooler fluid.

10. 10 3.2 Convection 2Convection and particle motion E When a fluid is warmed, the fluid particles move faster.  warm fluid expands  less dense than surrounding cold fluid  warm fluid rises  cool fluid from the top moves down to replace warm fluid  convection current

11. 11 3.2 Convection 2Convection and particle motion E Simulation

12. 12 3.2 Convection Warm air is taken in by the air conditioner & cooled. 3Examples of convection An air conditioner gives out cold air which falls. This pushes the warm air up. aAir conditioners

13. 13 3.2 Convection Land and sea breezes over the coast in the summer are caused by convection current. bSea-land breezes

14. 14 3.2 Convection bSea-land breezes During the day, the Sun heats up the land more quickly than the sea. Warm air rises Cool air blows in from the sea to replace it. wind warm air expands warm air cools

15. 15 3.2 Convection cShape of candle flame hot air rises Fire or flames always point upwards, since convection current flows upwards.

16. 16 3.2 Convection dSmoke detectors When there is a fire, Smoke rises and enters the detector. It triggers the alarm.

17. 17 3.2 Convection 3Examples of convection

18. 18 3.2 Convection 1Matters of which of the...Matters of which of the... 2When liquid/gas is warmed...When liquid/gas is warmed... 3Draw the convection current...Draw the convection current... Check-point 2 E

19. 19 3.2 Convection ASolids BLiquids CGases Check-point 2 – Q1 Matters of which of the following states cannot have convection?

20. 20 3.2 Convection convection less Check-point 2 – Q2 When liquid/gas is warmed, the warmer liquid/gas expands and becomes _______ dense than the surrounding liquid/gas. Hence, it rises. The surrounding cooler liquid/gas moves to replace the warm liquid/gas. Such liquid/gas movement forms a ____________ current. E

21. 21 3.2 Convection Check-point 2 – Q2 Draw the convection current formed in water when we boil water.

22. 22 3.2 Convection The End

23. 23 3.2 Convection In a fire, why should we crawl close to the floor in a smoke-filled room? Smoke is warmer than the surrounding air. Example 3 It rises & its places would be replaced by the surrounding cooler air. Smoke is toxic. We should crawl close to the floor to prevent smoke inhalation. Why do we crawl on ground during a fire?

24. 24 3.2 Convection Return