1. DIAGRAM Connecting Science © Hodder Education 2009

2. DIAGRAM Connecting Science © Hodder Education 2009 How a vacuum flask works Use the hot spots for the labels on the diagram to find out how the vacuum flask minimises heat loss by conduction, convection and radiation.

4. DIAGRAM Connecting Science © Hodder Education 2009 Vacuum The narrow gap between the two silvered walls is evacuated – it contains no air. There is no convection in this vacuum space. No heat can be transferred by conduction in the vacuum space. Return to diagram

5. DIAGRAM Connecting Science © Hodder Education 2009 Plastic stopper Conduction can only occur at the points where the walls meet the rest of the flask. Trapped air between the plastic cup and the stopper acts as an insulator. This reduces heat transfer by conduction and convection. Return to diagram

6. DIAGRAM Connecting Science © Hodder Education 2009 Silvered walls The walls around the vacuum flask are made of glass with a silvery coating made of aluminium. The shiny surfaces reduce heat loss by radiation (radiated energy is reflected off shiny surfaces). The walls could also be made of stainless steel, which can be polished. Return to diagram

7. DIAGRAM Connecting Science © Hodder Education 2009 Cork support Conduction can only occur at the points where the walls meet the rest of the flask, at the top and through the supports. Cork is a good insulator. It reduces heat loss by conduction. Return to diagram