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 transfer?

  • Proportion of input energy converted to useful output
  • Useful energy output is considered useful
  • Waste energy is non-useful energy output
• What is the equation for calculating efficiency?

  Efficiency = useful energy output / total energy input
• How can efficiency be calculated using power?

  Efficiency = useful power output / total power input
• If a lamp has an input energy of 300 joules, what is the useful energy output for an incandescent bulb that converts 45 joules?

  45 joules
• What is the useful energy output for a modern LED bulb with an input of 300 joules that converts 225 joules?

  225 joules
• How do you calculate the efficiency of the incandescent bulb?

  45 joules / 300 joules
• What is the efficiency of the incandescent bulb if it converts 45 joules from 300 joules?

  0.15
• How do you calculate the efficiency of the LED bulb?

  225 joules / 300 joules
• What is the efficiency of the LED bulb if it converts 225 joules from 300 joules?

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

  5 times
• What mistake should you avoid when calculating efficiency?

  Getting the division the wrong way around
• What happens if you calculate efficiency incorrectly?

  You get a value greater than one
• What does an efficiency rating of 1.33 or 133% imply?

  More energy out 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
• How do you convert efficiency from decimal to percentage?

  Multiply by 100
• What are the efficiency percentages for the incandescent and LED bulbs?

  15% and 75%
• How do you convert efficiency from percentage to decimal?

  Divide by 100
• What is the relationship between efficiency and waste energy?

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

  • Devices designed to produce heat
  • Example: Electric heaters
  • Thermal energy is useful output
• What type of energy does a lamp convert its input energy into?

  Light energy and heat energy
• How is light energy classified in a lamp's output?

  As useful energy output
• How is heat energy classified in a lamp's output?

  As waste energy or non-useful output