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AQA GCSE 1a-3 Electrical Energy

AQA GCSE 1a-3 Electrical Energy. AQA GCSE Physics pages 50 to 61 AQA GCSE Science pages 254 to 265. January 10 th 2011. AQA GCSE Specification. ELECTRICAL POWER, COST & DISTRIBUTION 11.3 Why are electrical devices so useful? Using skills, knowledge and understanding of how science works:

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AQA GCSE 1a-3 Electrical Energy

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  1. AQA GCSE 1a-3Electrical Energy AQA GCSE Physics pages 50 to 61 AQA GCSE Science pages 254 to 265 January 10th 2011

  2. AQA GCSE Specification ELECTRICAL POWER, COST & DISTRIBUTION 11.3 Why are electrical devices so useful? Using skills, knowledge and understanding of how science works: • to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application. • to calculate the amount of energy transferred from the mains using, energy transferred = power × time (kilowatt-hour, kWh) (kilowatt, kW) (hour, h) • to calculate the cost of energy transferred from the mains using, total cost = number of kilowatt-hours x cost per kilowatt-hour Skills, knowledge and understanding of how science works set in the context of: • Examples of energy transformations that everyday electrical devices are designed to bring about. • Examples of everyday electrical devices designed to bring about particular energy transformations. • The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which the device transforms energy. • The power of an appliance is measured in watts (W) or kilowatts (kW). • Energy is normally measured in joules (J). • Electricity is transferred from power station to consumers along the National Grid. • The uses of step-up and step-down transformers in the National Grid. • Increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.

  3. Electrical energy Electrical energy is useful because it is easy to transform into useful forms of energy.

  4. Electrical devices How many electrical devices can you spot in this picture?

  5. Some uses of electrical energy Light bulb Light Heat Electric heater Heat Light Electric motor Kinetic & potential Heat & sound iPod Sound Heat Hairdryer Heat and kinetic Sound

  6. Electrical devicesNotes questions from pages 50/254 & 51/255 • Why is electrical energy useful? • Copy four items from the table on page 50/254. • Copy and answer questions (a), (b) and (c) on page 51/255. • Copy the Key Points on page 51/255. • Answer the summary questions on page 51/255.

  7. In text questions: Electrical energy transforms to kinetic energy of the brush, thermal energy due to friction between the moving parts and resistance, and sound (i) microphone (ii) a loudspeaker An amplifier Summary questions: 1. Electrical, thermal, light 2. 1C, 2C, 3A, 4B Electrical devicesANSWERS

  8. Electrical power The electrical power of a device is a measure of how quickly the device uses electrical energy. electrical power = electrical energy time electrical power is measured in watts (W) 1 watt means I joule per second also: 1 kilowatt (kW) = 1 000 watts 1 megawatt (MW) = 1 000 000 watts

  9. Electrical power ratings These are always shown on an electrical device along with voltage and frequency requirements.

  10. Power comparisons Torch 1W Electric kettle 2 000 W or 2 kW Car 50 000 W or 50 kW Space rocket 100 000 000 W or 100 MW Power station 10 000 MW The Sun 100 000 000 000 000 000 000 MW

  11. Question 1 Calculate the power of a light bulb that uses 2400 joules of electrical energy in 60 seconds. electrical power = electrical energy time = 2400 J 60 s electrical power = 40 watts

  12. Question 2 Calculate the energy used in joules by a toaster of power 2kW in 5 minutes. electrical power = electrical energy time becomes: electrical energy = power x time = 2 kW x 5 minutes = 2000 W x 300 seconds electrical energy used = 600 000 joules (or 600 kJ)

  13. Answers Complete: 20 W 10 000 J 40 s 300 W

  14. Choose appropriate words to fill in the gaps below: Electrical energy is convenient to use as it is easily____________ into useful forms of energy. Electrical energy is measured in ________, symbol J. The electrical _________ of a device is equal to the rate at which a device transforms ___________ energy to other forms of energy. Power is measured in _________, symbol W. A one kilowatt device uses one ____________ joules of electrical energy every __________. transferred joules power electrical watts thousand second WORD SELECTION: second transferred power thousand watts joules electrical

  15. Electrical powerNotes questions from pages 52/256 & 53/257 • What is meant by ‘power’? • Copy the equation for power on page 52/256 stating clearly the units used for each quantity in the equation. • Copy and answer question (a) on page 53/257. • Copy the table on page 53/257. • Copy and answer questions (b) and (c) on page 53/257. • Copy the Key Points on page 53/257. • Try summary questions 1, 2 & 4 on page 53/257.

  16. In text questions: 5000W (5kW) 100 Probably not, as 100W would keep one or two light bulbs on, but only when you pedal Summary questions: 1. (a) (i) a mains filament lamp (ii) A 10 000W electric cooker (b) 6 million kilowatts 2. (a) 100 000J (b) 0.12 (or 12%) 4. 12 000 kJ Electrical powerANSWERS

  17. Paying for electricity An electricity meter is used to measure the usage of electrical energy. The meter measures in kilowatt-hours (kWh) A kilowatt-hour is the electrical energy used by a device of power one kilowatt in one hour.

  18. Question Calculate the energy used in joules by a hairdryer of power 1kW in 1 hour. electrical power = electrical energy time becomes: electrical energy = power x time = 1 kW x 1 hour = 1000 W x 3 600 seconds electrical energy used = 3 600 000 joules (or 3.6 MJ)

  19. Calculating cost 1 . Calculate kilowatt-hours used from: kilowatt-hours = kilowatts x hours 2 . Calculate cost using: cost in pence = kilowatt-hours x cost per kWh Electricity currently costs about 12p per kWh

  20. Question 1 Calculate the cost of using an electric heater of power 2kW for 5 hours if each kWh costs 12p. kilowatt-hours = kilowatts x hours = 2kW x 5 hours = 10 kWh cost in pence = kilowatt-hours x cost per kWh = 10 kWh x 12p = 120p cost of using the heater = £1.20

  21. Question 2 Calculate the cost of using a mobile phone charger power 10W for 6 hours if each kWh costs 12p. kilowatt-hours = kilowatts x hours = 10W x 6 hours = 0.01 kW x 6 hours = 0.06 kWh cost in pence = kilowatt-hours x cost per kWh = 0.06 kWh x 12p cost of using the heater = 0.72p

  22. Electricity bill Calculate the cost of the electricity that you use over a three month period (90 days). Typical power values: energy efficient light bulb – 15 W desk-top computer – 300 W hairdryer – 2 kW television – 100 W charger – 10 W Example: light bulb used for 4 hours per day: kWh = (0.015 x 4 x 90) = 5.4 kWh; cost = 5.4 x 12p = 64.8p

  23. Electricity Bill - eChalk BBC Bitesize Revision: The cost of using electricity - includes energy cost calculation applet Simulations

  24. Using electrical energyNotes questions from pages 54/258 & 55/259 • Define what is meant by the ‘kilowatt-hour (kWh)’ • Explain why a 2 kW heater uses 6 kWh when used continuously for three hours. • Copy and answer question (a) on page 54/258. • How many joules of energy are there in 1 kWh? • What does a domestic electricity meter measure? • Copy and answer questions (b) and (c) on page 55/259. • Electricity has become more expensive recently. Repeat question (c) this time for units costing 12p each. • Copy the Key Points on page 55/259. • Answer the summary questions on page 55/259.

  25. In text questions: 2.4 kWh Checked £100.94 (12p units = £173.04) Summary questions: (a) kilowatt; (b) kilowatt-hours; (c) kilowatt-hour, kilowatt, hour (a) (i) 1.5 kWh; (ii) 0.5 kWh; (iii) 0.8 kWh (b) 19.6 p 3. 4 kW Using electrical energyANSWERS

  26. The National Grid The National Grid is the network of cables connecting power stations to our homes and other buildings. The advantage of such a grid of cables is that more than one power station can be used to supply our electricity.

  27. Voltage levels Power stations produce electricity at 25 000 V. This is increased to up to 400 000V by step-up transformers. The voltage is decreased near our homes at local sub-stations to 230V by step-down transformers.

  28. Why high voltage levels are used. Electrical cables have resistance (like friction) which causes electrical energy to be transformed into waste heat energy when an electric current flows. Energy wastage to heat decreases when the voltage used is increased because the electric current is decreased. However, the higher the voltage the greater is the danger and the larger the pylons that have to be used to carry the cables.

  29. Repairing ‘live’ power lines Underground or overground cables? Advantages of underground cables: • They would not look unsightly. • They would not be subject to weather for example wind and ice. • They would not be a hazard to aircraft • They would be less accessible to vandalism or terrorism. Advantages of overground cables: • They are easier to put up than burying cables below ground or under rivers and canals. • They are easier to maintain and repair.

  30. Choose appropriate words to fill in the gaps below: The National Grid is a network of ______ that connects power _______ to electricity users. Power stations produce electricity at _______ which is increased by _______ transformers to up to 400 kV. Near electricity users, __________ transformers are used to decrease the voltage to down to _______. High voltages __________ energy loss to heat due to the resistance of the power cables to electric _________. cables stations 25 kV step-up step-down 230 V decrease current WORD SELECTION: stations 230 V decrease step-down 25 kV cables step-up current

  31. The National Grid - includes animated power station diagram Simulations

  32. The National GridNotes questions from pages 56/260 & 57/261 • What is the ‘National Grid’? • Copy figure 2 on page 56/260. • What is the purpose in the National Grid of: (a) step-up transformers and (b) step-down transformers. • What is the reason why a very high voltage is used on power lines? • Copy and answer question (a) on page 57/261. • List the advantages and disadvantages of burying cables underground. • Copy and answer question (b) on page 57/261. • Copy the Key Points on page 57/261. • Answer summary questions 1 & 3 on page 57/261.

  33. In text questions: Electrical energy would be wasted in the cables. Less electrical power would be supplied to the consumers. Faults would be harder to find. The ground would need to be dug up to make the repair. Summary questions: (a) Up, bigger (b) Down, smaller 3. (a) The higher the voltage, the smaller the current for the same power delivered. The power wasted due to the heating of the cables is much less for a smaller current. (b) The grid voltage has to be stepped-down for use in homes. Step-down transformers are needed at the sub-stations. The National GridANSWERS

  34. Essential electricity issuesNotes questions from pages 58/262 & 59/263 • Answer questions 1, 2, 3 and 5 on pages 58/262 and 59/263.

  35. Essential electricity issuesANSWERS 1. Too much current would be pushed through it and it would burn out. 2. (a) 1600 kWh (b) £112 3. Tubs and wooden paddles. 5. (a) Powergreen (b) Power Co.

  36. How Science WorksANSWERS • Correctly labelled graph with efficiency on the Y-axis and mass lifted on the X-axis. The line of best fit should be a CURVE. • As the mass increases, so does the efficiency, up to a point. Then the efficiency decreases with increasing mass. • Partial support. • Repeat measurements. • They have not been checked. • Having another person check the results / Using data from other sources / Using a different method.

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