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Energy Transfer Questions - GCSE Level

Q2.

(a) The diagram shows a ski jacket that has been designed to keep a skier warm. The jacket is made from layers of different materials.

(i) The inner layer is shiny to reduce heat transfer. Which process of heat transfer will it reduce? (1 mark)

Radiation

(ii) Why is the layer of fleece good at reducing the transfer of heat from a skier's body? (1 mark)

The examiner would not accept 'it's an insulator' or 'it reduces conduction and / or convection' or 'it doesn't allow heat to escape'. They want you to explain why is it good at doing these things.

The fleece traps (small pockets of) air, and air is a good insulator.

(b) A student tested four different types of fleece, J, K, L and M, to find which would make the warmest jacket. Each type of fleece was wrapped around a can which was then filled with hot water. The temperature of the water was taken every two minutes for 20 minutes.

The graph shows the student's results.

(b)

(i) In each test, the water cooled faster during the first five minutes than during the last five minutes. Why? (1 mark)

The cooling rate depends on the temperature difference. There is a bigger temperature difference (between the water and surroundings) at the start of the experiment (than at the end).

(ii) To be able to compare the results, it was important to use the same volume of water in each test. Give one other quantity that was the same in each test. (1 mark)

The starting temperature (of the water)

or

The thickness of fleece

The examiner did not accept the same 'amount' of fleece or equipment items such as the thermometer or can. Don't be vague in describing variables and avoid equipment as a variable. It can affect results in practice as sometimes cans could be made of different materials or be different dimensions and lab thermomeeters can be 'out' by a couple of degrees... but examiners like to assume there are no such problems with the equipment - look for a more obvious answer to the question!

(iii) Look at the graph line for fleece K. Estimate what the temperature of the water in the can wrapped in fleece K would be after 40 minutes. (1 mark)

Look at the graph. The water in J has reached room temperature already. After 40 minutes so would K.

18oC

(iv) Which type of fleece, J, K, L or M, should the student recommend to be used in the ski jacket? Give a reason for your answer. (2 marks)

M (if this is not chosen the second mark is not possible)

because it produces the smallest temperature drop, showing it was the best insulator.

(7 marks total)