20048 AC Science Year 6 Physical sciences

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How do wind and water generate electricity? Content focus: Energy transfer in the production of electricity Inquiry skills: Planning and conducting Processing and analysing data and information Communicating Background information • What is a hydro-electric power plant: A reservoir is an artificial lake that is constructed where a dam can be built at one end. The dam holds the water in the reservoir and houses the equipment for converting the water power into electricity. The water in the reservoir is still and so it has potential energy. Sluice gates control and measure the flow of water from the reservoir, down the penstock (a large pipe) to a turbine. As the water falls down the penstock, its potential energy is converted to kinetic energy. The further the water has to fall, the more kinetic energy it has and the more electricity it can produce. The height the water falls is called the head. The kinetic energy from the water flowing down the penstock is transferred to the blades of the giant turbine and causes them to tum, becoming mechanical energy which is 'doing work'. The turbine is connected to a generator in the power plant. As the turbine spins, it transfers its energy to the generator. As the generator spins, it converts its energy to electricity ( using electromagnetism). The water is either pumped back into the reservoir to be used again or it continues downstream. • Wind farms: Longer turbine blades have the capacity to generate more electricity as they can capture more of the wind's energy. Wind turbines are always tall because wind is stronger higher from the ground. • The blades of a turbine have an air foil design. (One surface is rounded while the other is f l at.) As wind moves across the rounded surface, it has to move faster to meet the wind that passes over the flat surface. • The major parts of a wind turbine are: - the rotor: As the wind pushes against the rotor blades, they absorb some of its kinetic energy and begin to tum. This makes the rotor hub spin with rotational energy. As the rotor spins, it transfers its energy to the shaft which begins to spin. As the shaft spins, it transfers its rotational energy to a generator - the generator: The generator converts the shaft's rotational energy into electricity as it passes through a magnetic field. Electricity is fed into the main electricity grid through a transformer - the nacelle: This is the casing that houses the shaft and the generator where the electricity is produced - an anemometer: Located in the nacelle, this measures wind speed. The turbines tum on and off automatically, working only between speeds of 15 and 90 km/h the tower: This supports the hub and the nacelle. It must be tall enough for the blades to clear the ground and to catch strong winds. Most towers are between 20 m and 30 m tall - the insulated cables that run down the tower and carry electricity from the generator to the transformer. • Useful websites: - http://www.intemationalrivers.org/china/three-gorges-dam - - - Preparation • Discuss what students understand by the term 'energy' and its different forms; e.g. light, sound, electrical, mechanical. Ask: How do these compare and contrast? Discuss means of generating energyboth renewable (solar, geothermal, wind, water, tida l ) and nonrenewable sources ( coal, oil, natural gas). Revise electromagnetism. (Refer to page 69.) Answers Page 72 1. 1. converted 2. form 3. transferred 2. (a) (i) stored (ii) moving (b) (i) mechanical (ii) rotational (iii) electrical 3. The kinetic energy of moving water or wind, converts to mechanical energy, which turns the blades of a turbine. This gives the shaft attached to it rotational energy, causing it to spin. The spinning shaft is attached to a generator. As the magnet spins, it generates a current in the coil, which is electricity. 4. (a) A current in a wire generates a magnetic field and a moving magnetic field generates a current in a wire. (b) It is spinning and so the magnetic field around it also spins. 5. (a) A step-up transformer increases voltage; a step-down decreases voltage. (b) Step-up transformers are needed to increase the voltage, so the effect of loss of power over distance is reduced. Step-down transformers are needed to decrease the voltage to a safe level for domestic and commercial use. Science as a Human Endeavour question Use and influence of science Teacher check ©R.I.C. Publications Low Resolution Images Display Copy Page 73 1. Initially, the water from all holes travels a similar distance. As the carton empties and the pressure decreases, the distance the water travels from the uppermost hole also decreases. 2. As water has weight, the higher the column of water above the hole, the greater the weight; therefore, pressure forces the water out of each hole. The downward pressure is greatest on the water leaving the lowest hole and so it travels further. 3. By building the plant at the base of the dam, engineers are making the most of the water's potential energy. AUSTRALIAN CURRICULUM SCIENCE (Year 6) m www.ricpublications.com.au R.I.C. Publications ®
How do wind and water generate electricity? - I We all know what water is, but what exactly is wind? Wind is created by the sun. Land absorbs heat energy from the sun and warms the air around it. As the warm air rises (because it is less dense than cool air), cool air rushes in to take its place. This fast moving air is wind. So how can water and wind generate electricity? The answer is all about the transfer of energy. Everything has energy of some form. It can't be created or destroyed, but it can be converted from one form to another when it is transferred between things. When water is lying still in a reservoir, it has potential (stored) energy. But when it is rushing down towards the turbines of a hydro-electric power plant, the potential energy is converted to kinetic (moving) energy. In the same way, still air has potential energy that is converted to kinetic energy when a wind develops. To turn the huge blades on a tower, wind speeds need to be at least I 5km/h. To look at, hydro-electric power plants and wind farms are very different but the way in which they generate electricity is very similar. When moving water or wind hits the blades of a turbine, the kinetic energy converts to mechanical energy and causes the blades to move. The turbine is attached to a shaft. As the blades turn, their mechanical energy is converted to rotational energy, causing the shaft to spin. The spinning shaft is attached to a generator, which is a magnet surrounded by copper coils. ©R.I.C. Publications Low Resolution Images Display Copy The principle of electromagnetism is used to generate electricity. Just as a current in a wire generates a magnetic field around itself, so a moving magnetic field generates a current. Inside the generator, a magnet spinning inside a coil of copper wires generates a current in the coil-electricity! Electricity loses some of its power as it travels over a distance. To make sure it still has enough power when it reaches its destination, a step-up transformer boosts its voltage to a very high level. Huge metal towers called transmission towers support insulated cables that carry the electricity at this dangerously high voltage. Before it is connected for use, the electricity is passed through a step-down transformer, converting it to lower voltages that are safe for domestic and commercial use. Fi IAW-io-_, R.I.C. Publications ® www.ricpublications.com.au m AUSTRALIAN CURRICULUM SCIENCE (Year 6)
Page 1 and 2: Your partner in education YEAR 6 Ph
Page 3 and 4: Foreword Australian Curriculum Scie
Page 5 and 6: . Teachers notes FOUR-PAGE FORMAT (
Page 7 and 8: (g JeaA) :l:JN:11:JS Wn1n:JIUHn:J f
Page 9 and 10: _____ l_n_v_e_s_tigation format Tit
Page 11 and 12: How does electricity flow? - I Imag
Page 13 and 14: Connecting circuits Electrical circ
Page 15 and 16: What are electrical conductors and
Page 17 and 18: Conductor or insulator? All materia
Page 19 and 20: How do light globes work? - I There
Page 21: Electromagnetism unplugged! Electro
Page 25 and 26: Making the most of water power Hydr
Page 27 and 28: ©R.I.C. Publications Low Resolutio
Page 29 and 30: Solar-powered pathways Solar-powere
Page 31 and 32: Which energy sources for the future
Page 33: Sustainable energy sources on tap c

20048 AC Science Year 6 Physical sciences

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