# P3

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## Energy Sources

• a primary energy source is used in the form that it is found e.g biofuels, fossil fuels, nuclear fuel
• primary energy sources can transfer their energy to secondary energy sources e.g electricity
• most of our electricity is made from burning fossil fuels which are non-renewable
• this produces carbon dioxide, a greenhouse gas
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## Power

• Power is the amount of energy transferred in one second
• a power of one watt (W) transfers one joule of energy in one second, energy transferred(J)=Power(W)Xtime (S)
• Domestic energy is measured in kilowatt hours kWh, the energy transferred by a power of 1kW in an hour; energy transferred (kWh) = power (kW) X time (hours)
• the flow of electricity in a circuit is called current
• electric current in an appliance transfers energy to it from the power supply: Electrical power (W)= Current (A) X voltage (V)
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## Electricity

• current in a component transfers electrical energy into other useful forms
• current in the connecting wires wastefully transfers electrical energy to heat
• an electricity meter records the amount of electrical energy transferred into a house
• electricity is metered in kWh
• Electricity supplied to a component= power (kW)Xtime(hours)
• Cost of electricity= number of units suppliedX cost per unit
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## Energy diagrams

• Sankey diagrams show the energy transfers in a component, the sum of the energy transfers out of a component equals the input energy
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## Efficiency

• the efficiency of a component tells you the proportion of electricity that it transfers into a useful form
• efficiency= energy usefully transferred/total energy supplied
• ways of using less energy: use efficient cars, live in insulated houses, build efficient power stations
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## Generators

• moving a magnet near a circuit causes an electric current to flow in the circuit
• the current flows only when the magnetic field is changing
• power stations use this idea to produce mains electricity by generators
• a generator contains an electromagnet near a coil of wire, there is a voltage across the coil when the electromagnet spins
• power stations use primary fuels such as fossil nuclear and biofuels to boil water into steam
• the steam passes through a turbine making its shaft spin around the turbine shaft spins the magnet inside the generator
• the turbine spins the shaft of the generator to make electricity
• it spins by steam hot gas wind and water
• coal fired power stations do this by burning coal to transfer energy into water
• gas fired stations burn natural gas to make hot gas for a turbine, another turbine is spun by steam from water heated by the hot gas
• hydroelectric power stations use a jet of high pressure water at the base of a dam to spin a turbine
• wind driven power stations use convection currents in the atmosphere caused by the heating effect of the sun on the land

COAL BURNT IN FURNACE-->WATER HEATED TO PRODUCE STEAM --> JET OF STEAM TURNS A TURBINE --> TURBINE SPINS THE GENERATOR ---> ELECTRICITY PRODUCED BY GENERATOR

• nuclear power stations make high pressure steam by putting fuel rods close together in the reactor so they heat up, taking away the heat with high pressure water circulating around the rods, using the high pressure water to boil low pressure water in a boiler
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## Waste from power stations

• Waste from nuclear power stations is radioactive and a serious health risk
• Nuclear waste must be carefully stored until it becomes safe
• nuclear waste emits ionising radiation which affects body cells
• an object is only irradiated when it is placed in the path of radiation
• as object is contaminated if it is mixed up with radioactive material
• contamination can be a more serious hazard than irradiation because it is a longer exposure to radiation and is difficult to stop spreading
• ionising radiation cannot be seen or felt
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## Renewable energy sources

• hydroelectric schemes, wind turbines, and wave technology are renewable energy sources
• hydroelectric schemes ads- provide large amounts of electricity, can pump water back behind the dam to store energy disads- flood large areas of land, cost a lot to build
• Wind turbines ads- need very little maintenence disads- only useful where there is a lot of wind

The National Grid

• a network of cables that carries electricity throughout the UK
• the national grid carries electricity at a very high voltage to reduce wasteful energy transfers in the cables
• national voltage is 230V
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## Choosing the best source of energy

• energy sources that produce large amounts of electricity- fossil fuels, nuclear power, hydroelectricity, bio fuels
• energy sources reliant on the weather- wind, waves, solar
• energy sources that do not produce greenhouse gases- nuclear, wind, waves, solar, geothermal
• environmental impact- fossil fuels produce greenhouse gases, extracting them is dangerous, risk of pollition, wind farms can cause noise and visual pollution, hydroelectric dams flood large areas, nuclear power causes radioactive waste
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## Future energy demand

• switching off appliances at home when not being used reduces energy use
• vehicles factories and power stations emit less carbon dioxide if they become more efficient
• global demand in the future is likely to increase because there will be more people
• we should replace old power stations with efficient ones, use a mix of renewable sources as fossil fuels will run out
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