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Energy basics

Energy cannot be created nor destroyed but it can only be changed from one form to another- This is called the law of conservation of energy.

Many electrical appliances transform electricity into various other forms of energy, for example:

  • Thermal/heat energy
  • Light energy
  • Sound energy
  • Kinetic/movement energy

Some transfers are useful energy (one which the device was made for) and some are wasted energy (dissipated into the air).

The amount of useful transfers compared to the total input is the efficiency of the device.

The transfers can also be represented using Sankey diagrams. These are scale diagrams showing how much of the energy is transfered as useful energy and how much as wasted energy.


For this device, % Efficiency = 20/80 x 100%


So, the thicker the 'wasted' arrow, the less efficient the device is.