efficiency

• When a device or object is going through an energy change, some of the energy that is inputted is TRANSFERRED USEFULLY & some is dissipated or wasted.
• Efficiency:


  The proportion of the energy supplied, that’s transferred into the useful energy output.
• Efficiency = useful output energy transfer (joules) / total input energy transfer (joules)
• Efficiency = useful power output (watts) / total power input (watts)
• The efficiency of a device can be improved by REDUCING wasted energy transfers. Waste energy is mainly due to:

  • Friction between their moving parts
  • Air resistance
  • Electrical resistance
  • Sound

  Most of these lead to THERMAL energy being dissipated into the surroundings.

  • If you can minimise these, you can IMPROVE the EFFICIENCY of a device.
• The higher the efficiency, the higher the cost.

  • reducing the cost allows more solar panels to be bought.

  
• No device is 100% efficient. 

  A speaker has an input power of 30 W, but only 10 W is converted to sound energy.

  • the other 20W is used for electricity.
• The government has recommended that the sale of filament lamps should be banned, as they’re inefficient.
• The input energy of a lamp is going to be electrical energy.

  • The output will be split between light & heat energy
  • The purpose of a lamp is to provide light.
  • the light energy is considered as useful energy output
  • while the heat energy is the waste energy

  
• A car engine is 25% efficient. How much input energy produces 100J of useful energy?

  efficiency = (useful energy / total energy) x 100

  • 25% = (100J / total energy) x 100
  • 25% = 10000 / total energy
  • total energy = 10000 / 25% = 400J
• Oiling would affect the efficiency of the wind turbine, as it reduces friction, as a result less energy is waste in the form of heat.

  • This makes a larger proportion of energy to be useful, increasing the efficiency.
• People should be encouraged to use energy efficient electrical devices, so less energy is wasted to minimise the energy demand.