Efficiency

• Efficiency


  Measure of how much of the energy transferred to a device is usefully transferred to another energy store
• Devices have energy transferred to them, but only transfer some of that energy to useful energy stores
• Most energy transfers involve some waste energy
• Useful devices


  • They can transfer energy from one store to another
  • Some of the input energy is usually wasted by being transferred to a useless energy store, usually a thermal energy store
  • The less energy that is 'wasted' in this energy store, the more efficient the device is said to be
• Improving efficiency of energy transfers


  1. Insulating objects

  2. Lubricating them

  3. Making them more streamlined
• Efficiency equation


  Useful output energy transfer / Total input energy transfer
• Efficiency equation (alternative)


  Useful power output / Total power input
• Efficiency can be expressed as a decimal or percentage
• Useful energy output is not usually equal to total energy input
• No device is 100% efficient and the wasted energy is usually transferred to useless thermal energy stores
• Electric heaters are 100% efficient because all the energy in the electrostatic energy store is transferred to "useful" thermal energy stores
• Ultimately, all energy ends up transferred to thermal energy stores
• The less energy a device wastes, the higher its efficiency