Edexcel - London Examinations GCE, May 1997 - Paper 2 Question 5

 5.a) Method:

1. Pour equal volumes of hot water in each cup.

2. Place a thermometer in each can. (Punch a hole through the lid in cup D)

3. Start a clock and record the temperature of the water in each can every minute or so.

4. Keep doing this for about 20 minutes (or until the temperature of the water reaches room temperature).

 (7 marks)

b)

 I expect that the water in cup D retains the heat for the longest time i.e. the water takes longest to cool down while cup C cools most quickly. This is expected because cup C loses heat by radiation (being black) and by convection (as it has no lid). Cup C also loses heat by conduction through the bench. Cup D has a lid (reducing heat losses by convection). Since it is white it reduces heat loss by radiation, while the air space at the bottom reduces heat loss into the bench by conduction (as air is a bad conductor of heat). (6 marks)

c)

 (4 marks)

d) Cup D is also capable of keeping the lemonade cool for the longest time as it prevents heat transfer from the surroundings to the lemonade by conduction through the bench (as it has an air space at the bottom); by radiation as it is white (reflecting heat energy) and the lid prevents heat loss by forced convection. (3 marks)