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P1.3.1 Transferring electrical energy Mr D Powell Connection • • • Connect your learning to the content of the lesson Share the process by which the learning will actually take place Explore the outcomes of the learning, emphasising why this will be beneficial for the learner Demonstration • Use formative feedback – Assessment for Learning • Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex • Offer different ways for the students to demonstrate their understanding • Allow the students to “show off” their learning Activation Consolidation • Construct problem-solving challenges for the students • Use a multi-sensory approach – VAK • Promote a language of learning to enable the students to talk about their progress or obstacles to it • Learning as an active process, so the students aren’t passive receptors • Structure active reflection on the lesson content and the process of learning • Seek transfer between “subjects” • Review the learning from this lesson and preview the learning for the next • Promote ways in which the students will remember • A “news broadcast” approach to learning Mr Powell 2012 Index Sankey Diagrams This diagram represents energy transfer by the drill motor. The manufacturer claims the drill motor has an efficiency of 0.35. The drill motor is supplied with 3000 J of electrical energy when the hole is drilled. 1. What form of energy does A represent? 2. What does B represent and what forms of energy are included in it? 3. What is the useful energy transferred by the drill motor used for? 4. What is the useful energy from the drill motor? 5. What is the energy wasted by the drill? 1. 2. 3. 4. 5. Electrical wasted thermal / sound Kinetic 0.35x 3000J = 1050J (1-0.35) x 3000J = 1950J Mr Powell 2012 Index Further notes... P1.2.1 Energy and efficiency – Video Sheet P1.3.1 Transferring electrical energy a) Examples of energy transfers that everyday electrical appliances are designed to bring about. b) The amount of energy an appliance transfers depends on how long the appliance is switched on and its power. c) c) To calculate the amount of energy transferred from the mains using: E=Pxt a) To calculate the cost of mains electricity given the cost per kilowatt-hour. Mr Powell 2012 Index Which word links all of these images... Mr Powell 2012 Index Units & Quantities Match Up Energy Power Temperature Mass Force watt Joule kilogram Newton degree Celsius C kg N J W Mr Powell 2012 Index Power Formulae When we think about energy being transferred we can talk about it in terms of... 3J transferred 5kJ or 5000J transferred. But is that at a steady rate and for how long? To relate one energy transfer to another we often think in term of the Power or the rate of energy transfer... We often write this formulae without a division as... E = Pt E is energy transferred in joules, J P is power in watts, W t is time in seconds, s If thinking about electrical devices we use the units of; E is energy transferred in kilowatt-hours, kWh P is power in kilowatts, kW t is time in hours, h Power = Energy / time Mr Powell 2012 Index Power Practical... 1) This practical involves stepping on and off a box or step. Use bathroom-type scales and measure your weight . Then measure the height of the box or “step” . The gain of gravitational potential energy of someone stepping onto the box (in joules) E = mgh (eq1) 2) Time how long it takes to make 50 steps onto and off the box. The gain of gravitational potential energy in making 50 steps on to the box; ET = 50 the gain in one step. ET = 50 mgh (from eq1) Power of your leg muscles = ET / time for 50 steps P = ET / t 3) Write down any calculations you have made and explain them 4) Why would the input power be more than the output power? Mr Powell 2012 Index Power Practical Example... h = 0.16 m - Height of one step t= 57s - Time to climb the stairs W = 560N - Your weight 50 = number of reps ET /t = Power Power = (50 mgh) / t = 50 x 560N x 0.16m / 57s = 80Js-1 = 80W This is the Power required or energy per second for 50 reps of a 0.16m box in a time of 57s Mr Powell 2012 Index Exam Question (C/D) A weight-lifter transfers 1000 J of energy to a weight when the weight is raised 1.6m in a time of 2.0 s. 1) What is the change in Potential Energy? 2) What is the mass lifted? 3) Calculate the energy per second transferred to the weight by the weightlifter? 1. 2000J 2. EGPE = mgh or EGPE /gh = m 1000J / 10 x 1.6m = 62.5kg 3. E = Pt so E/t = P 1000J/2s = 500W Mr Powell 2012 Index Exam Question II (B/C) In a hospital electronic arm an 800 W electric motor is used to raise a small load. In 120 s, the load gains 24 000 J of gravitational potential energy from the motor. What is; 1. 2. 3. 4. The electrical energy supplied to the motor. Energy wasted by the motor. The efficiency of the motor. The output power of the motor 1. 24,000J 2. E=Pt so E = 800W x 120s = 96,000J so energy wasted is = 96,000-24,000 = 72,000J 3. 24,000J / 96,000J = 0.25 or 25% 4. 800W x 0.25 = 200W Mr Powell 2012 Index Power & Efficiency... The table below shows the time taken by different electrical devices to transfer a given amount of energy supplied. The useful energy transferred in this time is also stated. Copy and Complete the table.... Device Time taken (s) Energy supplied (J) Useful energy transferred (J) useful power (W) Efficiency Lamp 1000 100 000 20 000 20 0.2 Microwave oven 120 96 000 48 000 400 0.5 Motor 300 18 000 6000 20 0.33 Computer 3000 900 000 100 000 33.3 0.11 Mr Powell 2012 Index What has happened here.... Mr Powell 2012 Index Understanding Electricity Bills Poor Dr Frankenstein did not look at his electricity bill and check the cost of each unit of electricity. What is a unit? Units are how we cost out electricity. 1 Unit = 1KW hour of electricity. They are shown on the bill here.. Mr Powell 2012 Index kWh & Appliances.... The idea of this is quite simple. We know that appliances transfer energy in Joules. We can represent this transfer over a period of time by saying the number of joules which flow in a certain time period. This brings us onto the idea of “Power” in watts or 1W = 1J/s. Also we can say that 1kW = 1000J/s Well if we take this further and say that a kilowatt hour is simply; 1 kW x 1 hour. So now by using this idea we can compare devices by their value of kw hours Mr Powell 2012 Index Examples of kWh A 200 watt T.V set ……..transfers 1 kWh of energy if it is switched on for 5 hours A 500 watt vacuum cleaner……..transfers 1kWh of energy if it is switched on for 2 hours Mr Powell 2012 Index kWh & Appliances.... Look at this example of three appliances. One old and two new The digital reading was taken to show their Power use over 24 hours. 1. Old Fridge Freezer - 3.93 kWh old Fridge/Freezer (roughly 6ft high, half fridge, half freezer) consumed 3.93 kWh’s in 24hrs. 2. New Fridge - 0.34 kWh new energy rating ‘A’ fridge (large fridge, 5ft high) consumes 0.34 kWh’s in 24hrs. 3. New Freezer - 0.46 kWh new energy rating ‘A’ freezer (normal under-counter size) consumes 0.46 kWh in 24hrs. Mr Powell 2012 Index kWh & Appliances.... Look at this example of three appliances. The digital reading was taken to show their Power 1. Old Fridge/Freezer = 3.93 x 10.668p = 42p per day = £153 per year. 2. New Fridge = 0.34 x 10.668p = 3.6p per day = £13 per year. 3. New Freezer = 0.46 x 10.668p = 4.9p per day = £18 per year. The saving would be £153 - £13 - £18 = £122 per year. That’s just the financial saving, add to this the environmental benefits Mr Powell 2012 Index Saving Energy You can save some energy by putting a device on standby. However, they still use a little bit of power. Here are some examples... DVD player on standby - 4 watts DVD player on but not playing - 10 watts DVD player playing a disk - 14 watts Laser Printer on standby - 3 watts Laser Printer Printing - 1000 watts Dehumidifier on standby - 9 watts Dehumidifier working - 170 watts Desktop PC - 112 watts PC Peripherals - 36 watts PC & Peripherals - 148 watts Sky+ on Standby - 13 watts Sky+ Playing - 20 watts Mr Powell 2012 Index Energy Costs... Look at this list of items and their cost in electricity. See if you can work out any costs of things that you do or how you can save energy. Write a list in your book? 12hrs PC and Peripherals - 1.76kWh = 18p per day = £68 per year 40 degrees wash - 0.77kWh = 8p per wash = £8.50 per year 60 degrees wash - 1.39kWh = 15p per wash = £15 per year 45 minutes walking on the treadmill - 0.21kWh = 2.2p Boil 1.7 litres of cold water - 0.19kWh = 2p Boil minimum level of cold water - 0.04kWh = 0.4p Toast 2 slices of bread - 0.04kWh = 0.4p 24hrs Sky+ on standby - 0.31kWh = 3.3p per day = £12 per Mr Powell 2012 Index Cost of electricity. If each unit of electricity costs 16p. Can you work out what each device cost? Power (kw) x time (hours) x cost per unit = monetary cost 38.4p 24p 16p 8p 0.8p Mr Powell 2012 Index Your School.... 2011 April 1 to 2012 March 31 Gass: Mainly heating the William Lee Block and for cooking. Fuel oil: Heating for the Main and Lower Schools, English and Technology Blocks. £16 197 (Previous year £15 616) 1. Cost of gas and fuel oil increased following rise in fuel prices. 2. Electricity costs reduced this year after the very large price rise last year and the renegotiation of the contract. £45 186 Previous year £43 055 Gedling Borough Council pay for the Leisure Centre and the Youth Wing on a 60:40 split so the total bill for the site was Electricity: Mainly lights, computers, air conditioning, etc. £75 310 (previous year £71 758) £25 803 What do you think? Previous year £32 813 Gedling Borough Council pay for the Leisure Centre and the Youth Wing on a 55:45 split so the total bill for the site was £59 660 (previous year £46 915). Mr Powell 2012 Index How can you explain these things... a) Examples of energy transfers that everyday electrical appliances are designed to bring about. b) The amount of energy an appliance transfers depends on how long the appliance is switched on and its power. c) c) To calculate the amount of energy transferred from the mains using: E=Pxt a) To calculate the cost of mains electricity given the cost per kilowatt-hour. P1.3.1 Transferring electrical energy Energy Power Tempe rature Mass Force Energy Power Tempe rature Mass Force watt Joule kilogram Newton degree Celsius watt Joule kilogram Newton degree Celsius C kg N J W C kg N J W P1.3.1 Transferring electrical energy - worksheet 8p 0.8p 0.8p 0.8p 16p 8p 0.8p 8p 24p 16p 8p 16p 38.4p 24p 16p 24p 38.4p 24p 38.4p 38.4p P1.3.1 Transferring electrical energy – worksheet Costs P1.3.1 Transferring electrical energy - worksheet Energy Power Tempe rature Mass Force watt Joule kilogram Newton degree Celsius C kg N J W 38.4p 24p 16p 8p 0.8p P1.3.1 Transferring electrical energy – worksheet Costs