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Connect the appliance to the power rating using an arrow! Appliance Kettle Iron Power rating (W) 1100W 65W Television 1800W Hair dryer 2000W Were you correct? Appliance Power Rating Kettle 2000 W Iron 1100 W Television 65 W Hairdryer 1800 W Kilowatt Hours (kWh) electrical energy used = power x time • A 100W light bulb on for 1 hour will use 100 Watt hours (Wh) of electricity • This is usually measured in Kilowatt Hours (kWh) 0.1 kWh • On an electricity bill, 1 unit of electricity = 1 kilowatt hour For example Drill 5kW on for 2 hours! 1kW costs 10p 1. Energy used = Power x time 2. Total cost= number of kilowatt hours x cost per kilowatt hour Energy used = 5kW x 2hours Energy used (kWh) = 10kWh Each kWh cost 10p so total is 10p x 10kWhr = £1.00 Kettle 2000W device = 2kW left on for one hour Hair dryer 1.5kW device left on for half an hour hour TV 500W device left on for three hours Light bulb 100W device left on for six hour Phone charger 1kW device left on for five hours How much does my electricity cost? Device Power Power in Time Number of units in watts kilowatt used used (W) (kW) (hours) Kettle 2000 2 1 Energy = Power x time 2 x 10p = Energy = 2 x 1 = 2kwh 20p Drill 5000 5 2 Energy = 5 x 2 = 10 Phone charger Normal Light bulb TV Hairdryer Total cost 10 x 10p = £1.00 Answers Device Power Power in Time Number of units in watts kilowatt used used (W) (kW) (hours) Kettle 2000 2 1 Energy = Power x time 2 x 10p = Energy = 2 x 1 = 2kwh 20p Phone charger 1000w 1kW 5 Energy = 1 x 5 = 5 5 x 10p = 50p Light bulb 100W 0.1kW 6 Energy = 0.1x 6 = 0.6 0.6 x 10p = 6p TV 0.5 3 Energy = 0.5 x 3= 1.5 1.5 x 10p = 15 p 1.5kW 0.5 Energy = 1.5 x 0.5 = 0.75 0.75 x 10p = 7.5p 500W Hairdryer 1500 Total cost Questions 1. Is it cheaper to have your kettle on for one hour a day or your light on for 6 hours? 2. Which device has the highest power rating? 3. What two things affect the amount of electricity a device uses? 4. How many watts are in one kilowatt? Eco versus normal? • To run a normal 100W light bulb for 5 hours a day all year costs: 100W x 5hours = 500Wh = 0.5kWh 0.5kWh x 12p = 6p 6p x 365 days = 2190p = £21.90 • To run a 15W eco bulb for 5 hours a day all year costs: 15W x 5hours = 75Wh = 0.075kWh 0.075kWh x 12p = 0.9p 0.9p x 365 days = 328.5p = £3.29 Electricity Meters How do we know how much electricity we use? We have meter readings that record what we use. We get charged either each month or 3 month period 2 1 1 3 2 8 3 2 How many units of electricity had been used by this family? Copy and complete • Power is measured in _________ (W) • The name for 1000watts is a_________(kW) • How much electrical energy is transferred depends on; - How ________an appliance is switched on for - How ________the appliance transfers energy (its power rating) Keywords; long; watts; kilowatts; fast HW - Is charging my phone expensive? Find out: What power your phone is How long it takes to charge The cost if it is 10p a unit