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Energy transfer and storage


Energy transfer diagrams

Energy transfer diagrams show the locations of energy stores and energy transfers. For example, consider the energy transfers in the simple electrical circuit below.

Complete circuit with battery powering lightbulb

We can show the transfers like this:

Battery (store of chemical energy) - energy is transferred as electrical energy to a lamp - energy is transferred as light energy to the surroundings

The battery is a store of chemical energy. The energy is transferred by electricity to the lamp, which transfers the energy to the surroundings by light. These are the useful energy transfers - we use electric lamps to light up our rooms.

But there are also energy transfers that are not useful to us. In the example above, the lamp also transfers energy to the surroundings by heating. If we include this energy transfer, the diagram looks like this:

Battery (store of chemical energy) - energy is transferred as electrical energy to the lamp. Some energy from the lamp is transferred as light energy to the surroundings, and some energy is transferred as thermal energy to the surroundings

Sankey diagrams

Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved. This Sankey diagram for the lamp shows that it transfers most of the energy by heating, rather than by light:

Electrical energy = 100J. 10J is used as light energy and 90J is used as heat energy

Notice that the total amount of energy transferred to the surroundings is the same as the amount of electrical energy. We say that the energy has been conserved. Energy is always conserved, it is never "lost" or "wasted", although some energy transfers are useful and some are not.


Energy transfer and storage activity

Transfer your energy into this activity.


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