Efficiency

• What can energy be transferred into?

  Different forms
• Why is energy not always transferred into the intended form?

  Devices aren't 100% efficient
• What is efficiency in terms of energy output?

  • Proportion of input energy converted to useful output
  • Useful energy output is considered light energy
  • Waste energy is considered heat energy
• How is efficiency calculated in terms of energy?

  Efficiency = useful energy output / total energy input
• How is efficiency calculated in terms of power?

  Efficiency = useful power output / total power input
• If a lamp has an input energy of 300 joules and outputs 45 joules as light energy, what is its efficiency?

  0.15
• If a lamp has an input energy of 300 joules and outputs 225 joules as light energy, what is its efficiency?

  0.75
• How many times more efficient is the LED lamp compared to the incandescent bulb?

  5 times
• How do you convert efficiency from decimal to percentage?

  Multiply by 100
• What happens if you get the division wrong when calculating efficiency?

  You get a value greater than one
• What does an efficiency rating greater than 100% imply?

  More energy output than input
• What principle states that energy can only be transferred?

  Conservation of energy principle
• If a microwave is 70% efficient with a total power input of 800 watts, what is the useful power output?

  560 watts
• What is a common characteristic of all devices regarding efficiency?

  • No device is 100% efficient
  • All devices produce some waste energy
  • Waste energy is often thermal energy
• What is an exception to the rule of efficiency in devices?

  • Devices designed to produce heat
  • Example: Electric heaters
  • Thermal energy is considered useful output