ENERGY

Energy and Efficiency – Efficiency, Energy transferred and Electrical costs

Energy and Efficiency – Efficiency, Energy transferred and Electrical costs

How efficient a device is refers to the proportion of energy that’s transferred usefully.

Efficiency can be calculated using the following equations.

  • For a decimal efficiency:

? efficiency = useful energy out / total energy in

  • For a percentage efficiency:

? (useful energy out / total energy in) x 100

The greater the percentage of available energy that’s transferred into useful energy, the more efficient the device. However, efficiency of a devise will never by 100%; some energy will always be wasted, as heat or noise.

NOTE: If you’re given power in watts (W) rather than energy in joules (J) the equations to use are the same. Simply use substitute power (W) for energy (J).

As you’ve seen already, a regular light bulb isn’t very efficient. How about an energy saving light bulb?

Light bulb Energy saving light bulb
Energy transfer diagram electrical energy ? heat and light energy electrical energy ? heat and light energy
Sankey diagram
Efficiency E = 100/5 x 100 = 5% E = 60/15 x 100 = 25%
Explanation An normal light bulb using a thin wire called a filament. This is heated by an electrical current at about 1100