Energy and energy resources (summary of AQA module)


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Energy and energy resources (summary of AQA module)

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Energy and energy resources (summary of AQA module)

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