Year 8 Science - Energy Flow Diagrams
An energy flow diagram is a visual way to show the uses of energy in a system. A simple diagram for the
energy flow in a mobile phone is shown below. This shows how energy is converted from one form into
another. The usable energy stored in the battery as chemical energy becomes degraded energy when
converted to sound, light and heat. Degraded energy is energy that is less usable.
Remember that the original energy stored in the battery has been converted from another form of energy
when the battery is charged.
Sankey Diagrams
Sankey diagrams are more useful because they indicate the amount of usable and wasted energy at each
stage of the diagram. Shown below are the Sankey diagrams for two types of light globes. Each of these
show 100 Joules of energy, added on the left, being converted into light energy and heat energy. Sankey
diagrams are named after Captain Matthew Sankey, an Irish engineer, who published the energy flow
diagram for a steam engine in 1898.
Filament Globe Light Emitting Diode, LED
Answer the following questions
Explain what you would mean by the expression, ‘energy efficiency of a light globe’.
