efficiency

• What does efficiency tell us about energy transfer?

  Fraction of energy transferred to useful forms
• What is the equation for efficiency?

  Efficiency = useful output / total input
• What is the second equation for efficiency?

  Efficiency = useful power output / total power input
• If an electric hob transfers 15,000 J of thermal energy and 12,000 J passes into water, what is the efficiency?

  0.8
• How can efficiency be expressed as a percentage?

  Multiply decimal efficiency by 100
• What is the efficiency of a bulb that has a power input of 60 W and a useful power output of 3 W?

  0.05 or 5%
• Why are LED bulbs considered more efficient than incandescent bulbs?

  More energy is transferred to light
• What happens to thermal energy when using a pan to heat water?

  Some energy is wasted to the air
• How does the material of a pan affect thermal energy transfer?

  Metal conducts heat better than plastic
• Why is a kettle more efficient than a pan for heating water?

  Less thermal energy escapes into the air
• What are ways to increase the efficiency of energy transfer?

  • Use a pan with a wider base
  • Use a lid on the pan
  • Place heating element inside water
  • Use materials with lower thermal conductivity