Energy, power & efficiency

• What is the concept of energy transfer discussed in the material?


  Energy can be transferred from one form into another form.
• Why is energy not always transferred into the intended form?


  Most devices aren't 100% efficient.
• What is efficiency in the context of energy transfer?


  • Proportion of input energy converted to useful output
  • Calculated as useful energy output divided by total energy input
• What type of energy does a lamp primarily output?

  Light energy.
• How is heat energy classified in relation to a lamp's output?


  Heat energy is considered waste energy or non-useful energy output.
• What is the formula for calculating efficiency?

  Efficiency = useful energy output / total energy input.
• How can efficiency be 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 useful 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 useful 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?


  The LED lamp is 5 times more efficient.
• How do you convert efficiency figures into percentage terms?


  Multiply the efficiency by 100.
• What is a common mistake when calculating efficiency?


  Getting the division the wrong way around.
• What happens if you calculate an efficiency greater than 1 or 100%?


  It implies more energy output than input, which is impossible.
• What is the conservation of energy principle?


  • Energy can only be transferred
  • Energy cannot be created or destroyed
• If a microwave has an efficiency of 70% and a total power input of 800 watts, what is the useful power output?


  The useful power output is 560 watts.
• What is a unique characteristic of devices designed to produce heat?


  • They produce thermal energy as a useful output.
  • Thermal energy is not considered waste in these devices.