P1 Revision 5

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  • Created by: LBC0502
  • Created on: 14-06-14 13:26
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  • P1 Revision
    • The Greenhouse Effect and Global Warming
      • Greenhouses gases include: carbon-dioxide, methane, nitrogen oxides and fluorinated gases (chlorofluorocarbons are responsible for depleting the ozone layer as the attack and destroy ozone molecules).
      • Why is it happening? The greenhouse effect is necessary for earth. The Sun's radiation is absorbed by the earth's atmosphere and some of the radiation is reflected back into the atmosphere. Without the greenhouse effect, there would be no life on earth (cold). The greenhouse effect increased during the Industrial Revolution with the development of the steam engine and car.
      • Causes: too much carbon-dioxide is put into the air. The combustion of coal and oil in our power stations/factories sends carbon-dioxide into the air. Too many trees are cut down (deforestation). In South America, huge areas of tropical forests have been cut down to make timber and to provide land for farming, leading to fewer trees to take in carbon-dioxide for photosynthesis.
      • Consequences: Temperatures will rise, increase in flash floods, contributes to global warming, glaciers will shrink, ice on rivers/lakes break up, plant/animal ranges shift, extreme weather patterns, more intense heat waves (Golf stream- Mexico to UK).
      • What is global warming? A gradual increase in the temperature of the earth's atmosphere, which is thought to be caused by the greenhouse effect (increased levels of CO2, CFCs and other pollutants.
      • What can we do about it? Reduce carbon emissions, plant more trees/vegetation, recycle, use less heat/air conditioning, use energy efficient products, use public transport, use less hot water, turn appliance off when not used, encourage others to conserve energy.
    • Electricity and Power
      • A motor transfers 10,000J of energy in 25s. What is its power?    E = 10,000J, T = 25s, P = ?. P = E ÷ T. P = 10,000 ÷ 25 = 400W
      • Power = Energy transferred ÷ Time. P = E ÷ T. (Formula Triangle)
      • What is the power of a lift motor that transfers 50,000J of energy from the electricity supply in 10s?            E = 50,000J, T = 10s, P = ?. P = E ÷ T. P = 50,000 ÷ 10 = 5,000 W
      • Power (energy used) is measured in Watts (W). Power is a measure of how quickly an appliance transfers energy e.g. J/s. The more energy transferred in a second, the more powerful the appliance is.
      • How to change Watts into kiloWatts: W?kW (÷1000). kW?W (x1000)
    • Paying for Electricity
      • A television uses 400W and is switched on for 2 hours. Calculate the energy transferred in kWh.            W ? kW ÷ 1000. E = ?. P = 400W÷1000 = 0.4kW. T = 2 hours. E = PxT. E = 0.4 x 2 = 0.8kWh
      • Paying for electricity: The electricity companies use the following: 1 unit = 1kWh. They will state the price per unit on the bill.
      • E = kW x h (kWh) (P=kW/T=h) Energy - J - kWh. Power - W - kW. Time - s - h.
      • A 4kW cooker is turned on for one hour. If the cost of a unit of electricty is 9p, calculate the total energy transferred.  E = ?. P = 4kW. T = 1 hour. E = PxT. E = 4 x 1 = 4kWh. 1 unit = 1kWh. 4 units = 4kWh. 4 units x 9p = 36p
      • A weight lifter transfers 100J of energy to a weight when the weight is raised in 2.0s. Calculate the energy transferred per second to the weight by the weight lifter.            E = 100J. T = 2.0s. P = ?. P = E÷T. P = 1000J ÷ 2 = 500W
    • Generating Electricity
      • Solar power: Solar cells and panels are made of semiconductor material (usually silicon) which captures lthe light energy and transforms it into electrical energy e.g. lights, fridges, calculators. Solar energy can produce electricity without turning a turbine
      • Wind power: Wind can be used to drive huge turbines, which in turn drive generators. Wind turbines are usually positioned on top of hils so they are exposed to as much wind as possible.
      • Tidal power: As the tide comes in, water flows freely through a valve in the barrage. This water then becomes trapped. At low tide, the water is released from behind the barrage through the gap that has a turbine in it. This drives the generator (every 12 hours, 6 hours high tide, 6 hours low tide)
      • Coal, oil and gas are non-renewable resources/ fossil fuels which contain chemical energy/carbon.
      • Geothermal power: Water is heated in the ground by radioactive decay in rocks to create steam. This steam can be used to drive generators.
      • Coal (chemical) burned in a furnace - Thermal energy to heat water (steam) - kinetic energy to turn turbine - generates electricity. (This is interchangeable). There is also a cooling tower to send cold water to be heated then, when the steam turns the turbines, it is sent to the cooling tower and the water is used again.
      • Hydroelectric power: Water this is stored in a reservoir above the power stations is allowed to flow down through the pipes to drive the generator which produces a lot of power.
      • Generating electricity involves turning turbines. The main sources of energy we use to make electricity is coal and gas in the UK. The source of energy we use least to make electricity is net imports.

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