Efficiency

• What is the equation for efficiency?

  Efficiency = Useful output energy (or power) / Total input energy (or power)

  Efficiency can also be expressed as a percentage by multiplying by 100.
• What is meant by the efficiency of a system?

  Efficiency is a measure of how much of the input energy (or power) is converted into useful output energy (or power), rather than being wasted.
• Why can no device be 100% efficient?

  Because some energy is always dissipated, usually as heat due to friction or resistance.
• How can the efficiency of a system be improved?

  Reducing friction (e.g., lubrication)

  • Reducing resistance (e.g., using low-resistance wires)
  • Reducing air resistance (e.g., streamlining)
  • Reducing unwanted sound or heat loss (e.g., insulation)
• If a motor has an input power of 500 W and an output power of 400 W, what is its efficiency?

  Efficiency = 400 / 500 = 0.8 (or 80%)
• What happens to the wasted energy in a system?

  It is dissipated into the surroundings, often as thermal energy, making the surroundings warmer.
• How is energy transferred in a light bulb, and what makes it inefficient?

  Electrical energy is converted into light (useful) and heat (wasted). The heat energy reduces efficiency.
• What type of diagram can be used to represent energy transfers in a system?

  A Sankey diagram, which shows input energy, useful energy output, and wasted energy output.