efficency

• What can energy be transferred into?

  One form into another form
• 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
• How do you calculate the efficiency of an incandescent bulb with 45 joules output and 300 joules input?

  • Efficiency = 45 joules / 300 joules
  • Efficiency = 0.15
• How do you calculate the efficiency of an LED bulb with 225 joules output and 300 joules input?

  • Efficiency = 225 joules / 300 joules
  • Efficiency = 0.75
• How many times more efficient is the LED lamp compared to the incandescent bulb?

  5 times more efficient
• 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 is the conservation of energy principle?

  • Energy can only be transferred
  • Energy cannot be created or destroyed
• How do you calculate useful power output from a microwave with 70% efficiency and 800 watts input?

  1. Convert efficiency: 70 / 100 = 0.7
  2. Use equation: Useful power output = 0.7 * 800 watts
  3. Result: 560 watts
• Why are most devices not 100% efficient?

  • All devices produce waste energy
  • Most often in the form of thermal energy
• What is an exception to the rule of devices not being 100% efficient?

  Devices that produce heat as their function
• What counts as useful output for electric heaters?

  • Thermal energy produced is useful
  • It is not considered waste energy