Electrical appliances

Many electrical appliances used in the home transfer electrical energy to other useful forms.

ApplianceUseful energyWasted energy
Electric kettleEnergy that heats the waterThermal energy store heating the kettle and infrared radiation transferred to the surroundings
HairdryerThermal energy store heating the air and kinetic energy of the fan that blows the airSound radiation, thermal energy store heating the hairdryer and infrared radiation transferred to the surroundings
Light bulbLight radiation given out by the hot filamentInfrared radiation transferred to the surroundings
TVLight radiation that creates images for the user and sound radiation that creates audio for the userThermal 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

A Sankey diagram showing the total energy in, wasted energy out and useful energy out.

Sankey diagrams show the energy transfers in a system:

  • the total energy transferred into the system is shown as an arrow
  • this arrow splits into narrower arrows showing other transfers

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.

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