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Energy and energy resources (summary of AQA module)


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Energy and energy resources (summary of AQA module)

Energy and energy resources (summary of AQA module)

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  • 1. Energy and energy resources summary 12 February 2011
  • 2. Thermal radiation
    • Hot objects emit thermal radiation (infra red rays) which are part of the electromagnetic spectrum.
    • The hotter an object is the more thermal radiation it emits.
    • Dark coloured, matt surfaces are better emitters and absorbers of thermal radiation (heat).
  • 3. Conduction
    • Heat can be conducted by a substance as one particle collides with the particle next to it.
    • Metals are very good conductors of heat because free electrons easily transfer the energy as they diffuse through the metal .
    • Non metals and particularly substances that contain air are very poor conductor (also called insulators )
  • 4. Convection
    • Convection occurs in fluids (liquids or gases) as the hot (lower density) fluid rises and the cooler (higher density) fluid sinks.
    • Convection cannot take place in solids because the particles are not free to move.
  • 5. Heat transfer
    • Heat can only pass through a vacuum by radiation since there are no particles in a vacuum to allow for conduction or convection.
    • Houses can be insulated against heat loss by wall insulation, double glazing, loft insulation and draft excluders.
    • Small objects (bigger surface area in relation to their size) lose heat faster than large objects
  • 6. Forms of energy
    • Energy can exist in a variety of forms:
    • Chemical energy – stored in food or fuel.
    • Kinetic energy – in moving objects
    • Gravitational potential energy – due to position of an object above ground.
    • Elastic energy – stored in springy objects
    • Electrical energy – carried by moving charges in a current.
    • Thermal energy – energy in particles of a hot object
  • 7. Transformation of energy
    • Energy can be transformed from one form to another.
    • When this happens no new energy is created or destroyed it simply changes form – this is called conservation of energy.
    • In many cases the energy is transformed into heat energy in the surroundings. As this happens the energy becomes more diluted and is very difficult to reuse.
  • 8. Useful energy
    • Useful energy is energy which is transformed for the purpose for which it was intended. Example electrical energy can be usefully converted into light.
    • Wasted energy – this is energy which is transformed into a form which was not intended and often results in the surroundings becoming warmer. Example – the electric light also heats the room. Wasted energy generally results in an effective loss of money.
  • 9. Efficiency
    • Energy is measured in Joules (or kilojoules)
    • Energy supplied = useful energy + wasted energy.
    • Efficiency = useful energy / total energy
    • Efficiency is often expressed as a percentage.
  • 10. Electrical devices
    • Electrical devices transform the kinetic energy of the moving charges in the current into various other energy types.
    • Examples are: light (lamps), heat (ovens), sound (radios), movement (motors).
    • Most electrical devices also waste energy – usually as thermal energy.
  • 11. Electrical power
    • The unit of power is the watt (W), 1 watt = 1 Joule/second.
    • 1 kilowatt (kW) = 1000 watts (W)
    • Power is the rate at which energy is transformed.
    • Formula:
    • Power (W) = energy (J) / time (s)
  • 12. Using electrical energy
    • Electrical energy used is measured in kilowatt hours (kWh).
    • 1kWh = 1000 watt appliance used for 1 hour.
    • Cost = number of units x cost per unit.
    • 1 unit costs about 15p at present – this is going up rapidly!
    • Example: Cost of using a 2000 watt heater for 3 hours will be:
    • Cost = 2kW x 3 hours x 15p = 90 pence
  • 13. The National Grid
    • The National Grid is the cables and transformers that supply homes and factories with electrical power.
    • Step up transformers are used to produce very high voltages in overhead cables (about 130000V) – this reduces heat loss in the cables because the current is very small.
    • Step down transformers are used to provide safe voltages (230V) for homes.
  • 14. Fuel for electricity
    • The diagram shows the basic parts of a power station. The heat is produced by often burning fossil fuels.
  • 15. Energy from wind and water
    • Wind and water can spin an electrical generator in these ways:
    • Wind turns the turbine blades.
    • Waves produce a rocking motion.
    • Water flows through tidal barrages and hydroelectric dams.
    • All these produce renewable, pollution free electricity but all can damage the environment and are unsightly.
  • 16. Energy from the Sun and the Earth
    • Solar cells can produce electricity when light falls on them – this is an expensive way to make electricity.
    • Solar panels can heat water.
    • Geothermal power stations use steam produced by radioactive substances underground drive a generator. This is a renewable energy source but is not available in many places.
  • 17. Energy and the environment
    • Burning fossil fuels like coal produce carbon dioxide (a greenhouse gas) and acid rain.
    • Nuclear fuels do not produce greenhouse gases and use a very small volume of fuel but the radioactive waste is very difficult to store and remains dangerous for many years.