Efficiency

• What is the definition of efficiency in a system?

  Measure of successful energy transfer
• How is efficiency defined mathematically?

  Ratio of useful power output to total power input

  
• What does high efficiency indicate about energy transfer?

  Most energy transferred is useful
• What does low efficiency indicate about energy transfer?

  Most energy transferred is wasted
• What determines whether energy is useful or wasted?

  Depends on the system
• In a lightbulb, what type of energy is useful?

  Light energy
• In a heater, what type of energy is useful?

  Heat energy
• What is the formula for calculating efficiency?

  Efficiency = (Power output / Power input) × 100

  
• What is power defined as?

  Energy transferred per unit of time
• What forms can energy take in the efficiency equation?

  Any form, e.g., gravitational potential energy
• How do you calculate the gravitational potential energy of a load?

  • Gravitational potential energy = mgh
  • Where:
  • m = mass (kg)
  • g = acceleration due to gravity (9.81 m/s²)
  • h = height (m)
• If an electric motor has an efficiency of 35% and lifts a 7.2 kg load through a height of 5 m in 3 s, what is the power output?

  117.72 W
• How do you calculate the power input if the power output is 117.72 W and efficiency is 35%?

  Power input = 336 W

  
• What are the examiner tips for efficiency calculations?

  • Efficiency can be a ratio or percentage
  • Convert ratio to percentage by multiplying by 100
  • Efficiency has no units
• What is the range of efficiency as a ratio?

  Between 0 and 1
• What is the range of efficiency as a percentage?

  Between 0% and 100%

  
• Why does efficiency have no units?

  It is a ratio with same units