# Energy Stores and Transfers Quiz

Do you know how energy is stored?

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## Energy Transfers

All energy is stored in some way before being transferred between stores. There are many types of energy stores including those which are most familiar to us:

Energy must move between these stores and each time energy is transferred there is an efficiency of transfer that is less than 100%. Often this leads to energy being dissipated into the environment as heat, sound and light. These waste energy transfers exist at different levels with some energy sources being more efficient than others.  Inevitably energy transfers with less than 100% efficiency lead to greater entropy in the Universe, according to the Second Law of Thermodynamics.

## Energy Transfer Diagrams - Sankey Diagrams

In order to explain energy transfers, we often rely on energy transfer diagrams and in particular, Sankey Diagrams. These show the amount of energy in Joules that is transferred and into which store they move, or how the energy is distributed between useful and non-useful forms of energy. The size of the arrows can be used to show the proportion of energy at each stage, with thicker or wider arrows indicating more energy being transferred.

On the right is an example of a Sankey diagram showing the energy transferred to a light bulb with electricity and the ways in which energy is transferred out of the light bulb and into the environment.

## Energy Transfers Examples

Below is a list of examples of simplified energy transfers between different types of energy stores. Remember that energy may transition between multiple stores along the way.

• Chemical energy in an electric vehicle’s battery is transferred to the kinetic energy of the car moving
• Chemical energy in a person’s muscles (ATP) is transferred to the kinetic energy of the person running
• Nuclear energy is transferred to electrical energy in a nuclear fission power station
• Gravitational potential energy is transferred to kinetic energy as a skydiver jumps from an aeroplane
• The kinetic energy of a train’s movement is transferred to thermal energy in the train’s brakes
• Electrical energy is transferred to gravitational potential energy when water is pumped into a storage reservoir at a higher altitude

Thermal energy is transferred by the mechanisms of conduction, convection and radiation.

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