Energy transfer diagrams

Energy transfer diagrams may be used to show the locations of energy stores and energy transfers. For example, consider the energy transfers in this simple electrical circuit:

Circuit with a battery and two lamps connected in series

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 internal energy (shown as chemical energy). The energy is transferred through the wires to the lamp, which then transfers the energy to the surroundings as 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 surroundings by radiation as infrared light, which increases the temperature of the surroundings. If we include this energy transfer (shown as thermal energy in the diagram), 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