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Heat Questions - GCSE Level

Q7. In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

In a question like this the examiner will be looking for several points explained using scientific keywords.

0 marks No relevant information
Level 1 (1-2 marks) A description of how at least one feature makes design A better than design B.
Level 2 (3-4 marks) A basic explanation in terms of physical processes of how some features of design A make it better than design B.
Level 3 (5-6 marks) A clear and correct explanation in terms of physical processes, including direct comparisons, of how most features of design A make it better than design B.


Solar panels use energy from the Sun to heat water. Two different designs of solar panel are shown in the diagram below. Both designs have the same water flow rate.

Explain why Design A is better than Design B at heating water.

 

(6 marks total)

The 'key' to getting high marks is to give what the examiner wants here - use the correct terms and only talk of things that relate to these diagrams - do not generally waffle about solar panels!

Solar panels take heat energy from the sun and transfer it to water - so you will be expected to talk about heat travel methods.

Transference of heat by radiation is most effcient via dark dull, matt surfaces - not shiny light ones.... and heat travels best by conduction via metals not insulators such as plastic. The labels in this diagram mention many of those words - highlight them on the diagram as you study it.

Notice also that in design A there is more water holding pipe in the panel than in design B.... you need to speak of the difference that makes - also only design A has insulation!

colour of pipe: the black (pipe) surface in design A is a good absorber of IR radiation / energy, whereas the white pipe in design B would be a poor absorber of the IR radiation. Therefore less energy would be given to the water inside the pipe.

material of pipe: metal pipes are better conductors of heat energy than plastic pipes so there will be a higher rate of energy transfer through the metal pipe in design A than the insulator pastic one of design B.

colour of surface of the panel also affects heat transfer: the inside of solar panel A is a white, shiny surface which is a good reflector of any infra red radiation from the sun that misses the pipe and hits the casing. It will refect some of that towards the pipe rather than it being absorbed by the casing.

Insulation: the layer of insulation around design A reduces loss of heat energy via conduction through base of solar panel.

length of pipe / surface area of pipe: The design of panel A provides a longer pipe than design B inside the panel. Water is therefore inside the solar panel for longer time and therefore the water will absorb more energy as it passes through the pipe.