Many electrical appliances used in the home transfer electrical energy to other useful forms.
|Appliance||Useful energy||Wasted energy|
|Electric kettle||Energy that heats the water||Thermal energy store heating the kettle and infrared radiation transferred to the surroundings|
|Hairdryer||Thermal energy store heating the air and kinetic energy of the fan that blows the air||Sound radiation, thermal energy store heating the hairdryer and infrared radiation transferred to the surroundings|
|Light bulb||Light radiation given out by the hot filament||Infrared radiation transferred to the surroundings|
|TV||Light radiation that creates images for the user and sound radiation that creates audio for the user||Thermal energy store heating the TV set and infrared radiation transferred to the surroundings|
The greater the amount of the supplied electrical energy transferred to useful energy stores, the more efficient the device will be. This can be shown in an energy transfer diagram or Sankey diagram.
Sankey diagrams show the energy transfers in a system:
Sankey diagrams are most useful when the amount of energy in each of the energy sources is known.
The width of the arrow is drawn to scale to show the amount of energy. Sankey diagrams show that the total energy transferred into a system is equal to the useful energy transferred plus the energy dissipated or 'wasted'. This confirms that energy is conserved.