Flashcards
Energy Production
Cards in this deck (42)
- 1Primary energy sourceA source of energy that has not been processed in any way.
- 2Secondary energy sourceA source that has been processed.
- 3Non-renewable energy sourceA finite energy source which is being depleted much faster than it can be produced, and so it will runt out. (fossil fuels e.g. coal and nuclear fuels e.g. uranium)
- 4Renewable energy sourceThis includes solar energy (and the other forms indirectly dependent on solar energy - wind energy, wave energy and bio fuels) and tidal energy.
- 5Specific energyThe amount of energy that can be obtained from a unit mass of a fuel. In S.I system = J/kg
- 6Energy densityThe amount of energy that can be obtained from a unit volume of a fuel. In S.I system = J/m^3
- 7Degradation of energyEnergy becoming less useful (cannot perform mechanical work anymore - still conserved)
e.g. thermal energy out of the exhaust of a car - 8Sankey diagramA pictorial energy-flow block diagram showing energy flows using arrows whose widths are proportional to the respective energy transfers.
- 9Efficiencyuseful energy/power out ÷
total energy/power in - 10Fossil fuel production- created over millions of years
- produced by decomposition of buried animal and plant matter
- high pressure and bacteria - 11Fossil fuel in energy production ADVANTAGESAdvantages:
- high energy density
- used directly and easily by a variety of engines and devices
- extensive distribution network in place - 12Fossil fuels in Energy Production DISADVANTAGESDisadvantages
- Release of greenhouse gases into the atmosphere
- serious environmental problems due to leakages along the production-distribution line (esp. oil)
- need for extensive storage facilities - 13Elec- only solar power goes directly to energy
- 14Nuclear Power
- 15Nuclear reactorA machine in which nuclear reactions take place, producing energy.
- "Fuel" typically uranium-235
- reaction: 1/0n + 235/92U ➝ 140/54Xe + 94/38Sr + 2 1/0n - 16Chain reactionThe fast neutrons produced in the fission of 235U are then slowed down and collide with other 235U nuclei in the reactor- producing more fission, energy and neutrons. The reaction is thus self-sustaining.
- 17Critical massThe minimum mass of uranium-235 for a chain reaction to sustain itself; with a lower mass, many neutrons escape without causing further reactions.
- 18Uranium enrichmentThe uranium commonly mined is 238U, which contains small traces (0.7%) of 235U.
Enrichment is the process of increasing the concentration of useful 235U in uranium sample.
- 5% enrichment for nuclear power plants
- 80% for nuclear weapons - 19Fuel rodsRods containing the nuclear fuel in pellet or powder form. In the case of uranium, the fuel rods contain a mixture of fissionable 235U and non-fissionable 238U.
- 20Control rodsThese rods can be inserted to absorb excess neutrons in order to control the rate of the fission reaction.
- 21ModeratorThe neutrons produced in the fission reaction must be slowed down if they are to be used to cause further fissions. This is achieved through collisions of the neutrons with atoms of the moderator, the material surrounding the fuel rods.
- 22Heat exchangethe kinetic energy of the reaction products is converted to thermal energy in the moderator. A coolant (e.g. water) passing trough the moderator can extract this thermal energy and use it to turn water to steam at high temperature and pressure. this can be used to turn the turbines of a power station, producing electricity.
- 23Advantages of energy production by nuclear fissionAdvantages:
- high power output (high energy density)
- large available reserves of nuclear fuel
- no greenhouse gas emissions - 24Disadvantages of energy production by nuclear fission- fast neutrons produced in a fission may be used to bombard uranium-238 and produce plutonium-239
- highly radioactive waste with long half-lives - difficult disposal
- even after shut down thermal energy produced (beta decay of product nuclei)
- potential major public health hazard - out of control ➝ meltdown
- Uranium ➝ Radon (carcinogen ➝ hazard in mining) - 25Photovoltaic system (solar to electric)- cells made out of semiconductors
- sunlight produces DC current/voltage on impact
- small current/voltage only - 26Solar active devices (solar to thermal)- used to heat water for domestic use
- simple, cheap
- bulky & cover a large area - 27Advantages/Disadvantages of solar energy productionAdvantages: unlimited energy supply, no extraction costs, clean
Disadvantages: only during day available, affected by weather, low energy density, requires large area, high initial cots (for photovoltaic systems) - 28Hydroelectric powermass = density x volume
potential energy = mass x gravity x height
Advantages: unlimited, no extraction cost, clean
Disadvantages: location-dependent, local environmental change, high initial costs - 29Wind powerrate of energy: P = 0.5pAv^3
Advantages: unlimited, no extraction costs, clean, practical for remote locations
Disadvantages: requires wind, visually intrusive, low-frequency operating noise intrusive, high maintenance costs - 30IntensityPower received per unit area: I = P/A. If a source emits equally in all directions, then, at a distance d from the source, the intensity is I=P/4πd^2.
- 31Solar constantThe intensity of solar radiation at the Earth's distance from the Sun, d(Earth).
- 32Black bodyA theoretical body that absorbs all the energy that is incident on it, reflecting none.
- 33Stefan-Boltzmann lawThe power emitted per unit area of a black body at an absolute (Kelvin) temperature of T is P = σAT^4
- 34Albedoα = reflected power ÷ total incident power
Albedo earth = 0.3 (reflects 30% of incident radiation)
Albedo is different depending on soil type, water depth, forestation and cloud cover. - 35Conduction- atoms at hot end increased vibration/temp
- collisions with neighbouring atoms transfers vibration/heat
- rate∝ cross sectional area
- rate ∝ temperature difference (T(H)-T(C))
- rate ∝1/width (L) - 36Convection- mainly fluids
- warmer fluid expands (∴less dense)
- rises up through Buoyant forces
- upward motion creates convection currents
- Examples: Sun's interior (bring gas to surface); weather patterns (oceans and atmosphere) - 37Radiation- can travel through a vacuum
- all bodies at given T(K) radiate electromagnetic waves over all wavelengths
- black and dull bodies (close to theoretical black body) use Stefan-Boltzmann law otherwise P=eσAT^4 - 38Power radiation/absorbtion- body at T(1) will radiate power at P (out) = eσAT(1)^4
- in surroundings at T(2) it will absorb power at rate P = eσAT(2)^4
- P(net) = P(out) - P(in)
- constant at T(1)=T(2) - 39Average intensity- the solar constant of S = 1400 W m^-2 is thought to be distributed over the entire surface of the earth
I(ave) = SπR^2/4πR^2 = S/4 = 350 W/m^2
30% reflected ∴ 250W/m^2 - 40The greenhouse effect- some radiation emitted by the earth 's surface gets absurd and re-radiated in all directions including the earth ➝ heating
- 41Mechanism of photon absorption by greenhouse gases- differences in molecular energy levels correspond to infrared photon energies
- radiation emitted by the earth is IR radiation and absorbed by molecules exciting the molecules to higher energy state - 42Greenhouse gases- water vapour ➝ evaporation (natural)
- CO2 ➝ forest fires, volcanic eruptions, evaporation of water from oceans (natural); burning fossil fuels, forests
- methane ➝ wetland, oceans, lakes and rivers; farm animals, burning biomass,
- nitrous oxide (N2O) ➝ soil, grassland, forests; fossil fuels, fertilisers
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- International Baccalaureate Physics Flashcards on Energy Production, created by Jonas Schlicht on 14/04/2016.
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- Jonas Schlicht
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