Efficiency

The standard formula for efficiency is the useful output divided by the total input, multiplied by 100 to give a percentage:


Efficiency=Useful OutputTotal Input×100Efficiency=Total InputUseful Output​×100


Key Rules


  • No Units: Efficiency is a ratio, so it does not have units. It is written as a decimal (between 0 and 1) or a percentage (between 0% and 100%).


  • Conservation of Energy: Efficiency can never be more than 100% because devices always waste some input energy as heat or sound.


Here is the efficiency formula from the OCS page

Efficiency in GCSE physics is the proportion of total supplied energy or power that is transferred into useful forms.


The Conservation of Energy

  • The maximum possible efficiency is 1 (or 100%).

  • No device can be more than 100% efficient.

  • Exceeding 100% breaks the law of conservation of energy (energy cannot be created or destroyed).

  • In the real world, no device is 100% efficient because energy is always dissipated (wasted) to the surroundings as thermal energy (heat), sound, or friction.


How to Improve Efficiency

  • Reduce friction: Use methods like adding lubrication to moving machine parts.

  • Reduce heat loss: Use insulation around thermal devices like kettles or hot water tanks.

  • Reduce air resistance: Streamline vehicles so less energy is wasted pushing air away.