A teacher presents his class with a polystyrene cup. The cup is formed from thick plastic containing many tiny pockets of air. He asks the class why the cup is so effective at keeping a hot drink warm. Three ideas are put forward. 1. It has air inside, and air is a poor thermal conductor. 2. The air is held in small bubbles, so very little convection can take place. 3. The plastic is a poor thermal conductor. Which ideas are correct?
- A1 and 2 only
- B1 and 3 only
- C2 and 3 only
- D1, 2 and 3