Topic 4 – Waves and the Earth

1. Topic 4 – Waves and the Earth

2. Ultrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. There are a number of uses for ultrasound: • Pre-natal scanning • Sonar • Communication between animals

3. Pulse-Echo techniques In pulse-echo techniques sound is reflected from an object to measure the distance to that object:

4. Pulse-Echo techniques - Ultrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. It can be used in pre-natal scanning, sonar techniques and as communication between _______: How does it work? Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object. Words – depth, reflected, picture, medium, animals

5. The Maths of Pulse-Echo x Consider shouting at a wall: The speed of sound is given by: v = 2x/t Therefore x = vt/2

6. The Maths of Pulse-Echo 25 50 75 100 125 150 175 200 t/μs The echo takes 0.8 seconds to return and the speed of sound in water is 1500ms-1. How deep is the water? Use the ultrasound scan to determine the width of the amniotic sac and the width of the baby’s body. The speed of sound in the fluid is 1500ms-1 and in soft tissue the speed is 1560ms-1.

7. Using an oscilloscope with ultrasound 20ms/div Consider a block of metal with a flaw: Q. If the speed of the ultrasonic wave is 3,000m/s how far away is the flaw from the detector?

8. Infrasound Infrasound is the region of sound BELOW 20Hz (as opposed to ULTRASOUND which is above 20KHz) – it can’t be heard by humans. Some uses: • Communication between animals • African elephants use infrasound to communicate with other elephants many kilometresaway. • 2) Detecting movement in remote areas • 3) Detecting volcanic eruptions and meteors

9. The Structure of the Earth A thin crust - 10-100km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid How do we know this? These facts have all been discovered by examining seismic waves (earthquakes)

10. Seismic waves Earthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types: • P waves: • They are longitudinal so they cause the ground to move up and down • They can pass through solids and liquids • They go faster through more dense material • S waves: • They are transverse so they cause the ground to move from right to left • They ONLY pass through solids • They are slower than P waves • They go faster through more dense material

11. Seismic waves These P waves travel through the Earth and are refracted when they pass through a medium These P waves are being reflected at the crust These S waves cannot travel through the outer core as they only go through solids The paths of these waves are all curved because density is gradually changing

12. Locating Earthquakes By measuring the time it takes the wave to travel to these locations the location of the earthquake can be found.

13. Movement of the Crust These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core. The Earth’s _______ is split up into different sections called ________ plates: Words – radioactive, crust, convection, tectonic, year

14. Plate Movements Earthquakes and volcanic eruptions can be common here Igneous Rock Oceanic Crust Mantle Convection Currents Magma

15. Topic 5 – Generation and Transmission of Electricity

16. Electric Current Note that electrons go from negative to positive and are “pushed” by the voltage + - e- e- Electric current is a flow of charge around a circuit By definition, current is “the rate of flow of charge”

17. Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter

18. More basic ideas… If a battery is added the current will ________ because there is a greater _____ on the electrons If a bulb is added the current will _______ because there is greater ________ in the circuit

19. Electrical Power P V I Power is defined as “the rate of transferring energy” and is measured in units called “Watts” (W). The amount of power being transferred in an electrical device is given by: Power = voltage x current in W in V in A • How much power is transferred by a 230V fire that runs on a current of 10A? • An electric motor has a power rating of 24W. If it runs on a 12V battery what current does it draw? • An average light bulb in a home has a power rating of 60W and works on 230V. What current does it draw?

20. Fuels Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils. A “fuel” is something that can be burned to release heat and light energy. The main examples are:

21. Some definitions… A renewable energy source is clearly one that can be _______ (“renew = make again”), e.g. _____, solar power etc. A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel. Words – non-renewable, coal, fossil fuels, wood, renewed

22. Using non-renewable fuels in power stations 1) A fossil fuel is burned in the boiler 2) Water turns to steam and the steam drives a turbine 3) The turbine turns a generator 4) The output of the generator is connected to a transformer 5) The steam is cooled down in a cooling tower and reused

23. Efficiency of Power Stations Heat Heat Heat 15J Boiler Turbine Generator 100J 50J 5J 85J 35J 30J Heat Kinetic Electrical

24. Pollution When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide. Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned. Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations. Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels. Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas, rainwater, burn

25. Nuclear power stations The main difference is that the nuclear fuel is NOT burnt – it is used to boil water in a “heat exchanger” These work in a similar way to normal power stations:

26. Start up times Quick Slow Different power stations have different start up times: Gas Oil Coal Nuclear

27. Non-renewable energy sources Coal, oil, gas and nuclear Advantages Disadvantages Pollution – CO2 leads to global warming and SO2 leads to acid rain Cheap fuel costs Generate a lot of energy Fuel will run out Easy to use

28. Renewable energy sources Wind, tidal, solar etc Advantages Disadvantages Often depend on the weather – is it sunny??? Clean Won’t run out Look ugly Energy is “dilute” – in other words, it’s very spread out Easily accessible

29. Other ways of generating electricity Can we drive the turbine directly without burning any fossil fuels?

30. Wind Power

31. Tidal Power Low tide High tide

32. Wave Power

33. Hydroelectric Power

34. Biomass

35. Biofuels Biomass can be used as a fuel in a number of ways: • Fast-growing trees that can be ____ • Manure or other waste that can be used to release _______ (biogas) • Corn or sugar cane that can be broken down in a fermenter to produce ______ like bio-ethanol. Biofuels have two main advantages over traditional fuels – they are ______ and ________. However, they still release ______ _______. Words – alcohols, cleaner, burnt, renewable, methane, carbon dioxide

36. Solar Energy Solar panels – convert sunlight directly into electricity. Sunlight knocks electrons loose from the crystal structure and the loose electrons form an electric current. The amount of power depends on the area of the panel and the light intensity. Heating for homes – these pipes carry water that absorbs heat energy and transfers it to the house.

37. Geothermal Energy

38. Geothermal Energy Geothermal energy can be used in _______ areas such as ______. In a geothermal source cold water is pumped down towards ____ _____. The water turns to steam and the steam can be used to turn ______. In some areas the _____ rising at the surface can be captured and used directly. Words – steam, Iceland, volcanic, turbines, hot rocks

39. Solar Panels and Thermal Towers

40. Using Solar Energy in remote places

41. Electromagnetic Induction N • The direction of the induced current is reversed if… • The wire is moved in the opposite direction • The field is reversed • The size of the induced current can be increased by: • Increasing the speed of movement • Increasing the magnet strength

42. Electromagnetic induction • The direction of the induced current is reversed if… • The magnet is moved in the opposite direction • The other pole is inserted first • The size of the induced current can be increased by: • Increasing the speed of movement • Increasing the magnet strength • Increasing the number of turns on the coil

43. AC Generators N S Voltage Time

44. Other generators A dynamo works by the same principle. 1) How can you make its output bigger? 2) How can you reverse the direction of its output current?

45. Large-scale production of Electricity A generator at Drax power station in England

46. DC and AC V DC stands for “Direct Current” – the current only flows in one direction: Time 1/50th s AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 230V T V

47. The National Grid Step up transformer Step down transformer Homes Power station Electricity reaches our homes from power stations through the National Grid: If electricity companies transmitted electricity at 240 volts through overhead power lines there would be too much ______ loss by the time electricity reaches our homes. This is because the current is ___. To overcome this they use devices called transformers to “step up” the voltage onto the power lines. They then “____ ____” the voltage at the end of the power lines before it reaches our homes. This way the voltage is _____ and the current and power loss are both ____. Words – step down, high, power, low, high

48. Power Lines Here’s my new shed. I want to connect it to the electricity I my house. Should I use an overhead cable or bury the cable underground?

49. Transformers Voltage across primary (Vp) No. of turns on primary (Np) Voltage across secondary (Vs) No. of turns on secondary (Ns) Transformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil. Words – alternating, magnetic field, induce, step up, voltage We can work out how much a transformer will step up or step down a voltage:

50. Some transformer questions