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
• 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 a lamp with given inputs?

  1. Identify input energy (e.g., 300 joules)
  2. Identify useful output energy (e.g., 45 joules for incandescent)
  3. Use formula: efficiency = useful output / total input
• What is the efficiency of an incandescent bulb that converts 45 joules from 300 joules?

  0.15
• What is the efficiency of an LED bulb that converts 225 joules from 300 joules?

  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 calculate efficiency incorrectly?

  You may get a value over 1 or 100%
• What does an efficiency rating over 100% imply?

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

  Conservation of energy principle
• How do you calculate useful power output from efficiency and total power input?

  1. Rearrange efficiency equation: useful power output = efficiency × total power input
  2. Convert efficiency to decimal (e.g., 70% = 0.7)
  3. Plug values into equation
• What is the useful power output of a microwave with 70% efficiency and 800 watts input?

  560 watts
• Why are most devices not 100% efficient?

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

  Devices that produce heat as their function
• What type of energy do electric heaters produce?

  Thermal energy
• How is thermal energy classified in electric heaters?

  As useful output