Energy - Transfer by Heating

Energy transfers can be represented in different ways. One of these is by an energy transfer diagram. This has three parts and usually only shows the main useful energy transfer. The first part of the diagram indicates the energy input, for example, chemical energy in the fuel for a car engine.

The second part of the diagram shows the process (in our example, this would be a picture of a car engine). The third part indicates the useful energy output from the engine which is the kinetic energy.

A different way of representing energy transfers is a Sankey diagram. This is most commonly used to represent energy efficiency as it is drawn to scale and shows the useful energy transfers and the waste energies. A Sankey diagram is sometimes presented on squared paper, with each square representing a specific quantity of energy; other times, it is just drawn as two or more arrows, with the energy values written on the arrows. You may be asked to work out the efficiency of an energy transfer from the figures on a Sankey diagram so make sure that you revise how to do that.

Where you come across questions about reducing heat losses from buildings, you are expected to know what U-values are and what they tell you plus how and why the various methods of insulation work. For example, loft and cavity wall insulation works by trapping air, since air is a poor conductor of heat, it slows down the speed at which heat leaves a building. Higher tier candidates would be expected to relate heat insulation to the kinetic theory. An example of this would be to show that you understand why warmer air rises and how conduction of heat occurs in solids.