2. 8.1 Energy degradation and power generation 1. Hot gas will cause the piston to move 2.But one stroke of the piston does not provide much energy 3.The process needs to be cyclical
3. Cyclical processes The continuous production of energy can be obtained from a cyclical process Not all of the heat can be converted to work Some is transferred to the surroundings
4. Efficiency of heat engines No heat engine can transfer all of it ’ s energy to work. Some is always lost as heat to the surroundings. Equation is not on the syllabus
5. Sankey diagrams You must be able to construct and analyse Sankey diagrams to show where energy is degraded. 100% 25%
8. The Generator Hyperlink Electrical energy is produced by the coils rotating in a magnetic field.
9. 8.2 World energy sources Which energy resources produce CO 2 ? Which are renewable? Which resources come from the sun? What are the advantages and disadvantages of the types of energy sources? (Location, cost, pollution, energy density, continuity, availability….) Define the energy density of a fuel Energy density is measured in J kg –1 .
10. World use of energy sources 91% Non-renewable Only approximate values are needed
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14. 8.3 Fossil fuel power production Outline the historical and geographical reasons for the widespread use of fossil fuels Students should appreciate that industrialization led to a higher rate of energy usage, leading to industry being developed near to large deposits of fossil fuels.
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17. Discuss the relative advantages and disadvantages associated with the transportation and storage of fossil fuels.
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19. Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.
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21. Chain reactions Each fission reaction releases neutrons that are used in further reactions. Fast neutrons Need to be slowed down Critical mass?
22. Distinguish between controlled nuclear fission (power production) and uncontrolled nuclear fission (nuclear weapons). Students should be aware of the moral and ethical issues associated with nuclear weapons.
23. Describe what is meant by fuel enrichment. Natural U-235 occurs as 0.7% abundance. (330 0 C) Enriched fuel contains 2.3% U-235, therefore increases the temperature (600 0 C)of the core of the reactor, therefore increases the efficiency and power output/Kg
24. Describe the main energy transformations that take place in a nuclear power station. E K of fission fragments
26. Discuss the role of the moderator and the control rods in the production of controlled fission in a thermal fission reactor. The moderator slows the neutrons down to enable them to allow fissions The control rods absorb neutrons to control the power level The heat exchanger isolates the water from the coolant and lets the hot gas boil the water . What are the energy transformations? graphite moderator boron control rod heat exchanger fuel element channel steel concrete hot gas reactor core cold gas charge face
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32. Solar power 1. photovoltaic cell There are 2 types of solar power In a sunny climate, you can get enough power to run a 100W light bulb from just one square metre of solar panel. Good for remote situations e.g. a yacht. 2. Solar water heating The Sun is used to heat water in glass panels on the roof This means you don't need to use so much gas or electricity to heat your water at home.
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42. Waves Volume of water in red area = a x λ /2 x L Mass = Volume x density( ρ ) Loss of GPE of the wave = mgh = (a x λ /2 x L x ρ ) x g x a Number of waves per sec = Frequency = v/ λ Power = loss of GPE per sec = a 2 x λ /2 x L x ρ x g x v/ λ Power per unit length = ½ a 2 ρ gv a λ L
48. Variations in albedo Sample albedos The albedo also varies with factors like season, latitude and cloud cover The average value on Earth is 0.3 Surface Typical Albedo Fresh asphalt 0.04 Conifer forest (Summer) 0.08,0.09 to 0.15 Worn asphalt 0.12 Deciduous trees 0.15 to 0.18 Bare soil 0.17 Green grass 0.25 Desert sand 0.40 New concrete 0.55 Fresh snow 0.80–0.90
49. Why does the reflected radiation not escape into space?
51. Absorption of IR radiation Carbon dioxide, water vapour , methane , nitrous oxide , and a few other gases are greenhouse gases. They all are molecules composed of more than two component atoms, bound loosely enough together to be able to vibrate with the absorption of heat. The major components of the atmosphere N 2 and O 2 are two-atom molecules too tightly bound together to vibrate and thus they do not absorb heat and do not contribute to the greenhouse effect. The resonant frequency of greenhouse gases is in the IR region
61. Values of emissivity Aluminium: anodised 0.77 Aluminium: polished 0.05 Asbestos: board 0.96 Asbestos: fabric 0.78 Asbestos: paper 0.93 Asbestos: slate 0.96 Brass: highly polished 0.03 Brass: oxidized 0.61 Brick: common .81-.86 Brick: common, red 0.93 Brick: facing, red 0.92 Brick: fireclay 0.75 Brick: masonry 0.94 Brick: red 0.90 Carbon: candle soot 0.95 Carbon: graphite, filed surface 0.98
62. What is the effect of the absorbed radiation on the temperature of the Earth?
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64. Climate change model Students should appreciate that the change of a planet ’ s temperature over a period of time is given by: (incoming radiation intensity – outgoing radiation intensity) × time / surface heat capacity.
