30/11/14 Topic 4 Waves and the Earth

Transcription

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: 1) Pre-natal scanning 2) Sonar 3) 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 Consider shouting at a wall: x The speed of sound is given by: Therefore v = 2x/t x = vt/2

6 The Maths of Pulse-Echo The echo takes 0.8 seconds to return and the speed of sound in water is 1500ms -1. How deep is the water? t/µs 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 Consider a block of metal with a flaw: 20ms/div 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: 1) Communication between animals African elephants use infrasound to communicate with other elephants many kilometres away. 2) Detecting movement in remote areas 3) Detecting volcanic eruptions and meteors

9 The Structure of the Earth A thin crust km 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: 1) They are longitudinal so they cause the ground to move up and down 2) They can pass through solids and liquids 3) They go faster through more dense material S waves: 1) They are transverse so they cause the ground to move from right to left 2) They ONLY pass through solids 3) They are slower than P waves 4) They go faster through more dense material

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

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 The Earth s is split up into different sections called plates: 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. Words radioactive, crust, convection, tectonic, year

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

15 Topic 5 Generation and Transmission of Electricity

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

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 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: P Power = voltage x current in W in V in A V I 1) How much power is transferred by a 230V fire that runs on a current of 10A? 2) An electric motor has a power rating of 24W. If it runs on a 12V battery what current does it draw? 3) An average light bulb in a home has a power rating of 60W and works on 230V. What current does it draw?

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

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 nonrenewable 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 100J Boiler 85J Turbine 35J Generator 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 These work in a similar way to normal power stations: The main difference is that the nuclear fuel is NOT burnt it is used to boil water in a heat exchanger

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

27 Non-renewable energy sources Advantages Cheap fuel costs Disadvantages Pollution CO 2 leads to global warming and SO 2 leads to acid rain Generate a lot of energy Coal, oil, gas and nuclear Easy to use Fuel will run out

28 Renewable energy sources Advantages Clean Disadvantages Often depend on the weather is it sunny??? Won t run out Wind, tidal, solar etc Look ugly Easily accessible Energy is dilute in other words, it s very spread out

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

30 Wind Power

31 Tidal Power High tide Low tide

32 Wave Power

33 Hydroelectric Power

34 Biomass

35 Biofuels Biomass can be used as a fuel in a number of ways: 1) Fast-growing trees that can be 2) Manure or other waste that can be used to release (biogas) 3) 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 1) The wire is moved in the opposite direction 2) The field is reversed The size of the induced current can be increased by: 1) Increasing the speed of movement 2) Increasing the magnet strength

42 Electromagnetic induction The direction of the induced current is reversed if 1) The magnet is moved in the opposite direction 2) The other pole is inserted first The size of the induced current can be increased by: 1) Increasing the speed of movement 2) Increasing the magnet strength 3) Increasing the number of turns on the coil

43 AC Generators Voltage N S 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 V DC stands for Direct Current the current only flows in one direction: DC and AC V Time 1/50 th s AC stands for Alternating Current the current changes direction 50 times every second (frequency = 50Hz) 230V T

47 The National Grid Electricity reaches our homes from power stations through the National Grid: Power station Step up transformer Step down transformer Homes 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 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: Voltage across primary (V p ) Voltage across secondary (V s ) No. of turns on primary (N p ) No. of turns on secondary (N s )

50 Some transformer questions Primary voltage V p Secondary voltage V s No. of turns on primary N p No. of turns on secondary N s Step up or step down? 12V 24V 100?? 400V 200V 20?? 25,000V 50,000V 1,000?? 23V 230V 150??

51 Some example questions Primary voltage V p Secondary voltage V s No. of turns on primary N p No. of turns on secondary N s Step up or step down? 6V 24V 100?? 400,000V 200V? 1,000? 25,000V? 20,000 20?? 230V 150 1,500? 1) A transformer increases voltage from 10V to 30V. What is the ratio of the number of turns on the primary coil to the number of turns on the secondary coil? 2) A step-down transformer has twice as many turns on the primary coil than on the secondary coil. What will be the output (secondary) voltage if the input voltage is 50V?

52 The Cost of Electricity Electricity is measured in units called kilowatt hours (kwh). For example A 3kW fire left on for 1 hour uses 3kWh of energy A 1kW toaster left on for 2 hours uses 2kWh A 0.5kW hoover left on for 4 hours uses kwh A 200W TV left on for 5 hours uses kwh A 2kW kettle left on for 15 minutes uses kwh

53 The Cost of Electricity To work out how much a device costs we do the following: Cost of electricity = Power (kw) x time (h) x cost per kwh (p) For example, if electricity costs 8p per unit calculate the cost of the following 1) A 2kW fire left on for 3 hours 2) A 0.2kW TV left on for 5 hours 3) A 0.1kW light bulb left on for 10 hours 4) A 0.5kW hoover left on for 1 hour 48p 8p 8p 4p

54 Reducing Energy Consumption 60W older bulb, roughly 70p, to be banned in the EU from ) Which one is more cost-effective? 25W energy efficient light bulb, 7.30 on Amazon 2) Jane wants to replace all the bulbs in her house with energyefficient ones. If she has 10 light bulbs in her house calculate the following: a) How much will it cost her to buy the bulbs? b) What will the total power consumption be reduced by? c) If she uses the bulbs for 5 hours per day and electricity costs 10p per unit how much money will she save? d) How long will it take her to repay the cost of the bulbs?

55 Energy and Power The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E E = Energy (in joules) P = Power (in watts) T = Time (in seconds) P T

56 Some example questions 1) What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? 2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? 3) Farhun runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? 4) How much energy does a 150W light bulb transfer in a) one second, b) one minute? 5) Shaun s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a physics lesson? 6) Damien s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day?

57 Topic 6 Energy and the Future

58 The 9 types of energy Type Heat Kinetic (movement) Nuclear Sound Light Chemical Electrical Gravitational potential Elastic potential 3 example sources

59 The Laws of Physics There are many laws of physics, but one of the most important ones is: Energy cannot be created or destroyed, it can only be converted from one form to another

60 3) An arrow about to be fired Energy changes To describe an energy change for a light bulb we need to do 3 steps: 1) Write down the starting energy: 2) Draw an arrow 3) Write down what energy types are given out: Electricity Light + heat What are the energy changes for the following? 1) An electric fire 2) A rock about to drop

61 Conservation of Energy In any energy change there is ALWAYS some waste energy: e.g. a light bulb: Electricity Light + heat In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use. Describe the following energy changes and state the waste energy or energies: 1) A vacuum cleaner 2) A TV 3) A dynamo/generator

62 Efficiency Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it. For example, consider a TV: Electrical Energy (200J) Light (80J) Sound (40J) Heat (?) Efficiency = Useful energy out Energy in x100%

63 Some examples of efficiency 1) 5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it? 2) A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go? 3) A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?

64 Energy Transfer ( Sankey ) diagrams Consider a light bulb. Let s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram: 100 J/s electrical energy Input energy Output energy 20 J/s light energy 80 J/s heat energy (given to the surroundings)

65 Example questions Consider a kettle: Consider a computer: 2000 J/s electrical energy Wasted heat 150 J/s electrical energy 20 J/s wasted heat Sound energy Heat to water 10 J/s wasted sound Useful light and sound 1) Work out each energy value. 2) What is the kettle s efficiency? 1) How much energy is converted into useful energy? 2) What is the computer s efficiency?

66 Radiation An introduction I m cool! I m very hot!

67 Some examples of radiation

68 Some examples of radiation

69 Heat Loss from a House

70 Radiation Practical Time / min Temperature in each container / 0 C Black Silver Clear

71 Radiation Radiation is when heat moves around in electromagnetic like light does. Any hot object will emit heat radiation the hotter it is, the more radiation it emits. This type of radiation is called. Dark, matt colours will absorb AND emit the infra-red radiation, and light, shiny colours will it. For a body to stay at constant temperature it must radiate the same average that it absorbs. Words reflect, infra-red, waves, most, power