Efficiency

• The efficiency of a system is a measure of the amount of wasted energy in an energy transfer

  Efficiency is defined as: The ratio of the useful energy output from a system to its total energy input

  • If a system has high efficiency, this means most of the energy transferred is useful
  • If a system has low efficiency, this means most of the energy transferred is wasted
  • Efficiency can be represented as a decimal or as a percentage
• Efficiency equations:

  A) useful

  B) total

  
• Improving Efficiency

  • The efficiency of a device can be improved by reducing wasted energy transfers
  • Machines waste energy due to:
  • Friction between their moving parts
  • Air resistance
  • Electrical resistance
  • Noise
• Reducing Friction

  • In a mechanical system, for example, there is often friction between the moving parts of the machinery
  • This results in unwanted energy transfers by heating to the machinery and the surroundings
  • Friction can be reduced by:
  • Adding bearings to prevent components from directly rubbing together
  • Lubricating parts
• Reducing Electrical Resistance

  • In electric circuits there is resistance as current flows through the wires and components
  • This results in unwanted energy transfers by heating to the wires, components and the surroundings
  • Resistance can be reduced by:
  • Using components with lower resistance
  • Reducing the current 
• Reducing Air Resistance

  • Air resistance causes a frictional force between the moving object and the air that opposes its motion
  • This results in unwanted energy transfers by heating to the object and the surroundings
  • Air resistance can be reduced by:
  • Streamlining the shapes of moving objects
  • For example, a racing cyclist adopts a more streamlined posture to reduce the effects of air resistance
• Reducing Noise

  • Sound is often created by moving parts of machinery
  • This results in unwanted energy transfers by heating to the surroundings as sound waves cause the particles in the air and nearby objects to vibrate
  • Sound can be reduced by:
  • Tightening loose parts to reduce vibration
  • Lubricating parts