1. Methods of Generating Electricity

2. Thermal power stations A thermal power station generates electricity by using the heat produced by the burning a fossil fuel such as coal, gas, oil or by the fission of uranium. What does a thermal power station do ?

3. Thermal power station block diagram BOILER Fuel is burnt to turn water into high pressure steam. TURBINE High pressure steam turns a turbine (like a windmill) GENERATOR The turbine rotates the coils of a generator to produce electricity. BOILERTURBINESGENERATOR Can you draw and explain it ?

4. Coal-fired power station

5. A Nuclear Reactor

6. Comparison of uranium and fossil fuels uraniumcoal, gas, oil Energy released per kg of fuel 1 000 000 kWh100 kWh Waste radioactive waste that needs to be stored for many years non-radioactive waste Greenhouse gases None Yes, mostly carbon dioxide

7. Renewable energy sources A renewable energy resource is one that will not run out. It is continually replaced. Renewable energy sources do not produce radioactive waste, greenhouse gases or acid rain. Examples include wind, hydroelectric, wave, tidal, solar and geothermal. Fossil fuels such as coal. gas and oil as well as uranium are non-renewable energy sources.

8. Wind power Wind is used to drive a turbine directly which rotates an electrical generator. A wind farm

9. Wind power versus thermal power stations ADVANTAGES Renewable energy source No greenhouse gases No acid rain No radioactive waste Inexpensive to build Short start up time DISADVANTAGES Unreliable – needs wind! Best used in places where they will often be regarded as unsightly Many turbines are needed to produce the same energy of a small thermal power station Noise Danger to wildlife

10. Wave power Waves can be used to drive an electrical generator.

11. Wave power versus thermal power stations ADVANTAGES Renewable No greenhouse gases No acid rain No radioactive waste No land needed Short start up time DISADVANTAGES Unreliable Can only be used in areas with suitable waves Prone to storm damage Many needed to produce the same energy of a small thermal power station Danger to shipping

12. Hydroelectric power Falling water is used to drive a turbine directly which rotates an electrical generator. The Hoover Dam near Las Vegas

13. Hydroelectric power station

14. Hydroelectric power versus thermal power stations ADVANTAGES Renewable Can produce as much energy as a thermal power station No greenhouse gases No acid rain No radioactive waste Short start up time DISADVANTAGES Can only be used in mountainous areas A large amount of land needs to be flooded Expensive to build Destroys animal habitats

15. Tidal power Moving water caused by the tides is used to drive a turbine directly which rotates an electrical generator. Proposed Severn Estuary Tidal Power Scheme Tidal power station at La Rance, Brittany

16. Tidal power station

17. Tidal power versus thermal power stations ADVANTAGES Renewable No greenhouse gases No acid rain No radioactive waste Short start up time DISADVANTAGES Very limited locations Wildlife affected Expensive to build

18. Solar power (cells) Electricity can be produced directly from the Sun’s radiation using solar cells.

19. Solar power (panels) Solar panels are used to heat water saving electricity or gas use.

20. Solar power versus thermal power stations ADVANTAGES Renewable No greenhouse gases No acid rain No radioactive waste Short start up time DISADVANTAGES Unreliable in the UK! – sunshine is needed for solar cells Can only be used during the day Only 10% of solar energy is converted into electricity by solar cells Many cells needed to produce the same energy of a small thermal power station

21. Geothermal energy In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy.

22. Geothermal versus thermal power stations ADVANTAGES Renewable No greenhouse gases No acid rain No radioactive waste Short start up time DISADVANTAGES Very limited locations Expensive to build

23. Electricity Generation pie-chart Most of our electricity is generated by burning fossil fuels (74% according to the pie chart opposite) Nearly 20% is nuclear Less than 5% is currently generated using renewable sources.

24. Problems with fossil fuels Burning coal, gas and oil produces carbon dioxide. This is a greenhouse gas which causes global warming. Fossil fuel burning can also produce sulfur dioxide gas. This can dissolve in water and produce acid rain which causes damage to forests and buildings. Modern power stations remove most sulfur dioxide producing compounds before burning. Fossil fuels are not renewable. They are running out. Estimates vary between 50 to 200 years to when we will need to find alternative sources of energy. An effect of acid rain

25. Problems with nuclear power stations Nuclear fuel (uranium) does not produce greenhouse gases and it generates 10000 times more energy per kilogram than fossil fuels. However: Nuclear waste is radioactive and may have to be stored safely for thousands of years. Power stations have to be decommissioned (dismantle and remove radioactive waste / materials / fuel ) Although safe in normal operation, accidents can release radioactive material over a large area. The area around Chernobyl in Ukraine has been closed off since 1986. The destroyed Chernobyl nuclear reactor

26. Pumped Storage Systems Why do we need pumped storage systems ? The demand for electricity varies throughout the day, if there is a sudden increase in demand water flows down and generates electricity quickly. The water is pumped back up at night when there is a low demand for electricity.

27. Pumped Storage Systems Is there any other way of coping with sudden increases ? Gas fired power stations have the quickest start up time, so they can be used to provide extra power above the base load. Base Load

28. What is the National Grid ? The National Grid The national grid is a system of cables and transformers.

29. Step-Up Transformer Step-Down Transformer The National Grid

30. Why do we use transformers ? By stepping up the voltage ( using the step up transformer) the current goes down. Low current means the wires don’t get hot so less energy is wasted.The voltage is then stepped down ( by the step down transformer ) to houses so its safer. The transformers make the system more efficient.

31. Waves for Communicating and understanding the Universe

32. Waves What are longitudinal and transverse waves ? In a transverse wave the oscillations are perpendicular to the direction of energy transfer. In a longitudinal wave the oscillations are parallel to the direction of energy transfer.

33. The wavelength of any wave is the distance between two matching points on neighbouring waves. Wavelength of a transverse wave The wavelength is the same whichever two matching points are used to measure this distance. wavelength The symbol used to represent wavelength is.

34. The amplitude of any wave is the maximum distance a point moves from its rest position. Amplitude of a transverse wave The amplitude of a transverse wave is the height of a peak or trough from the wave’s rest position of the wave. amplitude The larger the amplitude, greater the energy of the wave.

35. Investigating transverse waves

36. The frequency is the number of waves passing any point each second. frequency = number of waves past a point / time frequency is measured in hertz (Hz) 1 wave per second = 1 Hz 1000 waves per second = 1kHz 1,000,000 waves per second = 1Mhz 1,000,000,000 waves per second = 1GHz Frequency of transverse waves

37. Wave speed is measured in metres per second (m/s). What is the formula for wave speed? For any set of waves, the wave speed (v) can be calculated from the frequency (f) and wavelength ( ) using this formula: What are the units of speed, frequency and wavelength? Frequency is measured in hertz (Hz). Wavelength is measured in metres (m). wave speed = frequency x wavelength v = f x

38.   x A formula triangle helps you to rearrange a formula. The formula triangle for wave speed (v), frequency (f) and wavelength ( ) is shown below. Cover the quantity that you are trying to work out, which gives the rearranged formula needed for the calculation. So to find frequency (f), cover up f… …which gives the formula… Can I use a formula triangle? f = v

39. Wave calculations A microwave with a frequency of 2.4GHz travels at 3 x 108 m/s. What is its wavelength? 2.4 GHz = 2,400,000,000 Hz or 2.4 x 10 9 Hz wavelength = speed / frequency wavelength = 3 x 10 8 / 2.4 x 10 9 = 0.125 m Be careful with units – wavelength is in meters

40. Electromagnetic waves are transverse

41. As the wavelength of EM spectrum changes, the way the different wavelengths interact with matter also changes. As the frequency increases, wavelength gets smaller. Eventually the waves are so small that they can interact with cells, DNA and atoms. This is called IONISING RADIATION. IONISINGNON-IONISING

42. Uses of EM Waves WaveUses Radio waves Television and radio transmission Microwaves Mobile phones, cooking and satellite communication Infra red Thermal imaging, cooking, optical fibres, security systems TV Remote Control Visible light Vision, Photography Ultraviolet Detecting forged banknotes tanning, disinfecting water X-rays Medical images of bones Gamma rays Killing cancer cells, sterilising food and medical equipment

43. Harmful Effects of EM Waves WaveUses Microwaves Internal Heating of Body Cells Infra red Skin Burns Ultraviolet Skin cancer and Cataracts X-rays Mutation & damage to cells Gamma rays Mutation & damage to cells

44. Reflection Can you draw what happens to light when it is reflected by a mirror ? The angle of incidence is equal to the angle of reflection The normal is at 90 O to the mirror Your diagram must have arrows on the rays.

45. Reflection Can you draw how an image is formed in a plane mirror ? The image is the same distance behind as the object is in front The image is virtual ( its formed by those dotted lines)

46. Diffraction What is diffraction ? The spreading out of waves as they pass through a gap or around an object. Most diffraction when the gap is about the same size as the wavelength of the wave.

47. Sound What type of wave is a sound wave ? It is a longitudinal wave made up of squashes ( compressions) and stretches ( rarefactions)

48. Sound What happens when a sound wave hits an object ? It is reflected – we call this an echo.

49. Red Shift What does this diagram show? When a source of waves moves towards us the waves are squashed ( wavelength smaller, frequency higher) When a source of waves away from us the waves are stretched ( wavelength bigger, frequency lower)

50. Red Shift Why is the Doppler effect important? We observe that light from distant galaxies is shifted towards the red part of the spectrum – this must mean that they are moving away from us. The universe is expanding !.This also means that at some point in the past they must have been closer. ( Light from distant galaxies does not look redder)

51. Red Shift What is special about the expansion of the universe? The further a galaxy is from earth the bigger its red shift. This gives the examiner a chance to ask about distance and speed being directly proportional.

52. The Big Bang Theory What is the Big Bang Theory? The theory that the universe started as a tiny hot mass where all the matter in the universe was concentrated. The main evidence to support this theory comes from: Red shift and The Cosmic microwave background radiation. Remember that scientists cannot say what happened before the big bang because there is no evidence.

53. The Big Bang Theory What is the cosmic microwave background radiation? This is microwave radiation that fills the universe wherever you look. It comes from radiation produced by the big bang.