energy, power, and climate change summary

energy, power, and climate change summary - IB PHYSICS...

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IB PHYSICS SUBSIDIARY LEVEL ENERGY, POWER & CLIMATE CHANGE SUMMARY 8.1 Energy degradation and power generation Heat energy may be completely converted to work in a single process. Continuous conversion of heat energy into work requires a cyclical process and the transfer of some energy from the system. Degraded energy is less able to do useful work. When energy is degraded into heat that is transferred to the surroundings, it can not do useful work. A Sankey diagram shows the energy input, the energy output and the work done during a process. The production of electric power involves the rotation of a magnet near coils of wire or a rotating coil near magnets plus an energy source to cause the rotation. 8.2 World energy sources World energy sources include coal, oil, gas, nuclear, hydro, wood, solar, geothermal , wind, wave and tidal. Renewable energy sources can be used again e.g. wind and non-renewable energy sources cannot e.g. oil. The energy density of a fuel is equal to the number of joules released when 1 kg is burnt. Approximate percentage uses of different energy sources are oil 37, coal 25, gas 23, hydro 6, nuclear 6 8.3 Fossil fuel power production Industries and power stations are generally constructed next to large deposits of fossil fuels. The lower the energy density of a fuel, the greater is the amount used by a power station. Coal is transported to power stations in trains and trucks. Storage of coal is done in stacks that run a risk of fire. Oil is transported in tankers, trucks and pipelines which run the risk of leakage and spills. Natural gas is transported in pipelines that can leak. Efficiencies of power stations fuelled by fossil fuels are gas 38% coal 38% and oil 37%. Carbon dioxide and methane are two important Greenhouse gases that are emitted from power stations using fossil fuels. 8.4 Non-fossil fuel power production Nuclear Power If one neutron causes a U-235 nucleus to fission, about 3 neutrons are freed by the process. If all these are allowed to hit uranium nuclei, then 3, and then 9 and then 27 ... fissions will occur and a chain reaction starts. Neutrons leaving the lump of uranium through its surface will stop a chain reaction. There is a minimum sized lump called critical size needed for a chain reaction to occur i.e. about 50 kg. Before a chain reaction will start Controlled fission allows only one of the neutrons released during fission to go on and cause fission. In a weapon as many of the neutrons released as possible go on to cause fission so the number occurring increases.
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