1. Plenary
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Chapter 9 – Conduction, Convection and Radiation

2. Chapter 9 : Conduction, Convection and Radiation 1
Metals are good / poor conductors of heat because they have many / few ???? electrons in their structure.
The tiles on my bathroom floor feel cold under my feet, but the rug feels warm. Yet they’re both at the same temperature! Why do they feel different?
Name 3 ways to reduce the heat loss from a house.

3. Chapter 9 : Conduction, Convection and Radiation 1
Answers
Chapter 9 : Conduction, Convection and Radiation 1
Metals are good / poor conductors of heat because they have many / few ???? electrons in their structure.
The tiles on my bathroom floor feel cold under my feet, but the rug feels warm. Yet they’re both at the same temperature! Why do they feel different?
Name 3 ways to reduce the heat loss from a house.
free
It’s not a temperature question – it’s a conduction question. The rug is a poor conductor, so it doesn’t take heat away from my feet.
(any 3 sensible answers)

4. Chapter 9 : Conduction, Convection and Radiation 2
Explain why a hot air balloon can fly (3 marks)
Explain why two thin blankets keep you warmer than one thick blanket.

5. Chapter 9 : Conduction, Convection and Radiation 2
Answers
Chapter 9 : Conduction, Convection and Radiation 2
Explain why a hot air balloon can fly (3 marks)
Explain why two thin blankets keep you warmer than one thick blanket (3 marks)
Air heated by the burner expands(1), so it is less dense(1) than the surrounding air, so it tends to rise(1) marks
Simply ‘because hot air rises’ mark
‘Heat rises’ WRONG! No marks
Air is a poor conductor, so it is a good insulator(1) but only if it is trapped, to stop convection currents(1).
Two thin blankets will trap more air(1). 3 marks

6. Chapter 9 : Conduction, Convection and Radiation 3
Black / shiny surfaces absorb heat well.
Black / shiny surfaces emit heat well.
Conduction / convection / radiation is the main method of heat transfer in solids.
In a vacuum flask, - why has the air been sucked out from between the glass walls? what is the shiny layer for?

7. Chapter 9 : Conduction, Convection and Radiation 3
Answers
Chapter 9 : Conduction, Convection and Radiation 3
Black / shiny surfaces absorb heat well.
Black / shiny surfaces emit heat well.
Conduction / convection / radiation is the main method of heat transfer in solids.
In a vacuum flask, - why has the air been sucked out from between the glass walls? what is the shiny layer for?
To stop conduction and convection.
To reflect thermal radiation (infra-red).