Efficiency

• What happens to the energy that is not usefully transferred by the solar cells?

  Wasted
• Suggest one advantage of the aircraft having fuel cells as well as the solar cells.

  can fly at night
• Give one environmental advantage of using electric motors to drive the aircraft propellers rather than motors that burn a fuel.

  no greenhouse gases
• solar cells transfer light energy to .......................................................energy.

  electrical
• batteries transfer ............................................................. energy to electrical energy.

  chemical
• The LEDs transfer electrical energy to ............................................................. energy.

  light
• Turbine turns a coil in a…


  Generator
• Give one disadvantage of using a wind generator to charge a battery.

  wind speed may be too low to operate the generator
• State one factor, other than efficiency, that is important when considering the choice of a bulb for lighting in the home.

  availability of bulbs
• How does the design of the stove help to improve the rate of energy transfer by infrared radiation?

  black is a good emitter of infrared radiation

  large surface area
• Give two environmental advantages of using a wood burning stove to heat a home rather than heaters that use electricity generated from fossil fuels.

  wood is renewable

  wood is carbon neutral
• What is meant by an energy source being renewable?


  replaced faster than it is used
• Name two other renewable energy sources used to generate electricity.

  wind

  waves
• The step-up transformer increases the efficiency of the National Grid. Explain how.

  decreases the current reducing energy loss
• Suggest why it was important to confirm the efficiency independently

   

  to avoid bias
• Outline some of the advantages of using solar cells to generate this electricity.

  conserves fossil fuel stocks

  can be used in remote areas
• To make energy transfers more efficient, we have to maximise the useful energy and minimise the wasted energy from a transfer.
• Equations in terms of energy

  
• Energy is measured in joules, J
• Efficiency has no units
• Equation in terms of power

  
• Power is measured in watts, W
• Ways to increase efficiency

  thermal insulation

  lubrication

  streamlining
• 100% efficiency is usually impossible.
• There is usually always some wasted heat energy in the form of heat / thermal energy.