Conduction and Convection 05/01/2020

1. Conduction and Convection05/01/2020 Double Lesson Aim: • To explain the processes of conduction and convection Starter: • Touch all of the following objects in the lab • Which is the coolest and hottest? • Shirt • Stand • Bunsen Tube • Bunsen Chimney • Bench • Chair Leg

2. Heating and Cooling • insulator – a material that is hard for heat energy to flow through. • conductor – a material that is easy for heat energy to flow through due to its free electrons • fluid – a liquid or gas • Conduction • heat travelling by particles colliding together. • Main heat transfer mechanism in solids. • Fluids make bad conductors • Convection Currents • Main heat transfer mechanism in liquids • In your own words explain convection currents • In your own words explain convection currents • In your own words explain convection currents • In your own words explain convection currents • Radiation • Heat energy transfer by Infra Red electromagnetic waves (like visible light) • Does not need particles and is thus the only heat transfer mechanism in a vacuum

3. Conductors can be compared to see which is the best. The faster the heat travels through the rod the quicker the pins will drop. Rod 1 Rod 2 Wax melts and tells us that the heat has arrived

4. What happens when copper and steel are heated? Both steel and copper are good conductors. They are both metals and all metals are good conductors. Conduction of heat Steel Copper

5. What happens when copper and glass are heated? Glass will conduct heat but it is a non-metal. Non-metals are poor conductors (insulators). Conduction of heat glass Copper

6. Conduction Colder Hot Hot

7. Particle model for conduction As the solid gets hotter the particles vibrate faster. These extra vibrations are passed along the rod. This is how the heat spreads and we call this CONDUCTION Cold Hot NON-METAL

8. Particle model for the best conductors Positive ions pass the energy on by collision Metals also have free electrons METAL The free electrons move through the metal and help conduction. The electrons pass on energy by colliding with the ions (and other electrons)

9. Heating and Cooling • insulator – a material that is hard for heat energy to flow through. • conductor – a material that is easy for heat energy to flow through due to its free electrons • fluid – a liquid or gas • Conduction • heat travelling by particles colliding together. • Main heat transfer mechanism in solids. • Fluids make bad conductors • Convection Currents • Main heat transfer mechanism in liquids • In your own words explain convection currents • In your own words explain convection currents • In your own words explain convection currents • In your own words explain convection currents • Radiation • Heat energy transfer by Infra Red electromagnetic waves (like visible light) • Does not need particles and is thus the only heat transfer mechanism in a vacuum

10. Conduction in Fluids • A fluid is a liquid or a gas • Fluids do not conduct well • Demo Boiling water in your hand

11. Demos • 2 gas jars with hot water • Convection Loop

12. Heating a Gas

13. Look at this particle model of a liquid • How does the particle motion compare with solids? • How will heat spread through a liquid?

14. particles • become hot • gain kinetic • energy • spread out • particles • cool down • lose kinetic • energy • move closer Particles in a small region of water • more dense • water falls • (sinks down) • less dense • water rises • (floats up)

15. R Convection

16. Heating and Cooling • insulator – a material that is hard for heat energy to flow through. • conductor – a material that is easy for heat energy to flow through due to its free electrons • fluid – a liquid or gas • Conduction • heat travelling by particles colliding together. • Main heat transfer mechanism in solids. • Fluids make bad conductors • Convection Currents • Main heat transfer mechanism in fluids • In a paragraph or a set a notes explain convection currents • Radiation • Heat energy transfer by Infra Red electromagnetic waves (like visible light) • Does not need particles and is thus the only heat transfer mechanism in a vacuum

17. Convection Currents in Kettles

18. Tea Bag Demo • Remove all the tea leaves • Light the top of the bag

19. Think how heat will spread in these diagrams Heat Heat Heat Heat Heat Which way will the paddle wheels move?

20. Answers Heat Heat Heat Heat Heat clockwise anti-clockwise

21. Sea Breeze

26. Conduction and Convectionrecap Aim: • To explain the processes of conduction and convection

27. Radiation and Insulation05/01/2020 Aim: • To explain the processes of radiation • To identify the main mechanisms of insulation Starter: • How many senses do you have? • Can you feel where the sun is with your eyes closed?

28. How does heat get to us from the sun?

29. Some examples of Infra Red Movie - Walking in Woodland Man in Chair Movie - Firemen

30. Heating and Cooling • insulator – a material that is hard for heat energy to flow through. • conductor – a material that is easy for heat energy to flow through due to its free electrons • fluid – a liquid or gas • Conduction • heat travelling by particles colliding together. • Main heat transfer mechanism in solids. • Fluids make bad conductors • Convection Currents • Main heat transfer mechanism in liquids • In your own words explain convection currents • Radiation • Heat energy transfer by Infra Red electromagnetic waves (like visible light) • Does not need particles and is thus the only heat transfer mechanism in a vacuum • Black matt objects absorb and emit the most infra red radiation • Shiny white objects absorb and emit the least infra red radiation

31. Mini Practical • Wrap a dark piece of foil around one hand and a light one around the other • Which hand gets hot first when held near to a Bunsen?

32. Investigating thermal absorption

33. Investigating thermal emission

34. Heating and Cooling • insulator – a material that is hard for heat energy to flow through. • conductor – a material that is easy for heat energy to flow through due to its free electrons • fluid – a liquid or gas • Conduction • heat travelling by particles colliding together. • Main heat transfer mechanism in solids. • Fluids make bad conductors • Convection Currents • Main heat transfer mechanism in liquids • In your own words explain convection currents • Radiation • Heat energy transfer by Infra Red electromagnetic waves (like visible light) • Does not need particles and is thus the only heat transfer mechanism in a vacuum • Black matt objects absorb and emit the most infra red radiation • Shiny white objects absorb and emit the least infra red radiation

35. Infrared radiation – true or false?

36. Which type of heat transfer?

37. Insulation • Charlie forgot to take the chicken out of the freezer last night! • Will his plan to defrost the chicken in time for lunch work?

38. Effective Insulators • Think about the following effective insulating materials • What do they have in common? • Why are they good insulators? Duvet filling Hair Expanded polystyrene Cotton

39. Insulation • Insulation will slow down heat flow • Keep cold things cold and hot things hot • Some materials make good insulators (e.g. ceramics) • Most insulators are improved by: • trapping pockets of air • pockets are too small for convection currents • air is a bad conductor

40. How does a vacuum flask work? 3. The walls have silvery surfaces, which prevent heat leaving or entering by radiation. How is a vacuum flask able to keep hot drinks hot and cold drinks cold? 2. The plastic (or cork) lid is an insulator and the screw top prevents convectioncurrents escaping from the flask. 1. There is a vacuum between two layers of glass or steel, which prevents heat leaving or entering by conduction.

41. Movie

42. Multiple-choice quiz

43. Insulationrecap Aims • Identify that gases are poor conductors of heat. • Investigate the best way to insulate a test tube of hot water.

44. Insulating Homes05/01/2020 Aim • To name methods of insulating housing • To state what types of heat transfer they prevent • To explain how they work

45. Anagrams

46. Losing Energy We lose energy from the roof, the door, the walls and the windows. In order to reduce electricity bills and pollution, we need to keep energy losses from our homes to a minimum.

47. Home Insulation • As we go through the next few slides complete the table below • Don’t copy the words on the slides, read and summarise

48. Curtains Curtains reduce draughts [convection currents] leaving the house. They are opaque and so don’t allow much radiated heat to pass through them.

49. Home Insulation As we go through the next few slides complete the table below Don’t copy the words on the slides, read and summarise

50. Double Glazing A great deal of energy is lost through windows. By adding an extra pane, the trapped air in between acts as an insulator to reduce heat loss by conduction. The insulating effect of the gap can be improved further by sucking all the air out to create a vacuum. Double glazing is expensive and difficult to smash without a special hammer.