Physics- Efficiency

• Efficiency


  The fraction of the energy we put into an appliance that is transferred to useful forms of energy
• Calculating efficiency


  1. Useful output energy transfer / Total input energy transfer

  2. Useful power output / Total power input
• Efficiency greater than 1 or 100% is not possible
• Incandescent bulbs


  • Not efficient, most energy is transferred to thermal energy
• LED bulbs


  • More efficient, greater percentage of energy is transferred to light
• Increasing efficiency of heating water with a pan

  1. Use a pan with a wider base and a lid

  2. Place the heating element inside the water (like an electric kettle)
• Thermal conductivity


  How well a material conducts heat
• Plastic has lower thermal conductivity than metal, so less thermal energy is lost through the walls and lid of an electric kettle