efficiency

• What should you be able to calculate by the end of the video?


  The efficiency of energy transfer
• What does efficiency tell us about energy transfer?

  It tells us what fraction of the energy put into an appliance is transferred to useful forms of energy
• What is the equation for calculating efficiency?

  Efficiency = useful output energy transfer / total input energy transfer
• What is another equation for calculating efficiency?

  Efficiency = useful power output / total power input
• Are students provided with the efficiency equations in the exam?

  No, students need to learn the equations
• If an electric hob transfers 15,000 J of thermal energy and 12,000 J passes into the water, what is the efficiency?

  Efficiency = 12,000 J / 15,000 J = 0.8
• How can efficiency be expressed besides as a decimal?

  As a percentage by multiplying the decimal value by 100
• What is a common mistake students make when calculating efficiency?

  Writing the calculation upside down
• What happens if the efficiency calculation is done upside down?

  You will get a value greater than 1 or 100%
• If an electric current delivers 60 W to a light bulb and 3 W is transferred to light energy, what is the efficiency?

  Efficiency = 3 W / 60 W = 0.05 or 5%
• Why are traditional light bulbs considered inefficient?

  Most electrical energy is transferred into thermal energy, which is wasted
• How do LED bulbs compare to traditional bulbs in terms of efficiency?

  LED bulbs are much more efficient, transferring a greater percentage of energy to light
• What are some ways to increase the efficiency of energy transfer when heating water?

  • Use a pan with a wider base
  • Use a lid to reduce heat loss
  • Place the heating element inside the water
• What is a significant source of thermal energy loss when using a pan to heat water?

  Thermal energy passing into the air around the edges of the hob and at the surface of the water
• How does the material of the pan affect thermal energy transfer?

  Metal conducts heat well, leading to more thermal energy loss compared to plastic
• Why is a kettle more efficient than a pan for heating water?

  A kettle has less thermal energy passing through its walls and lid into the air
• What is thermal conductivity?

  It is a measure of how well a material conducts heat
• What resources are available for further practice on calculating efficiency?

  • Vision workbook
  • Additional questions available online
• What should students be able to do by the end of the video regarding energy transfer efficiency?

  Calculate the efficiency of energy transfer and describe ways to increase it