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<ul><li> Slide 1 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters Electricity meters </li> <li> Slide 2 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters Energy used is measured in kilowatt-hours (kWh) and is calculated by the following formula: energy transferred (kWh) = power (kW) time (hours) </li> <li> Slide 3 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters A television uses 400 W and is switched on for 2 hours. Calculate the energy transferred. Energy transferred= power time = (400 1000) kW 2 hours = 0.8 kWh </li> <li> Slide 4 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters A 150 W hi-fi is turned on for one and a half hours. Calculate the energy transferred. Energy transferred= power time = (150 1000) kW 1.5 hours = 0.225 kWh </li> <li> Slide 5 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters On your electricity bill, kilowatt-hours are called units of electricity. We can calculate the cost of electricity by using the formula: cost of electricity = energy transferred cost per unit </li> <li> Slide 6 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters A 4 kW cooker is turned on for one hour. If the cost of a unit of electricity is 9p, calculate the cost of the total energy transferred. Energy transferred= power time = 4 kW 1 hour = 4 kWh Cost of electricity= energy transferred cost per unit = 4 kWh 9p/kWh = 36 pence </li> <li> Slide 7 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters A computer uses 250 W and is turned on for 5 hours. If the cost of a unit of electricity is 10.2p, calculate the cost of the total energy transferred. Energy transferred= power time = (250 1000) kW 5 hours = 1.25 kWh Cost of electricity= energy transferred cost per unit = 1.25 kWh 10.2p/kWh = 12.75 pence </li> <li> Slide 8 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters The amount of electricity used in your home is recorded on an electricity meter. </li> <li> Slide 9 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters If the total cost of electricity for the period shown below is 19.72, calculate the cost per unit. In this example the cost per unit is the same for all units used. Total energy transferred= 72 516 kWh 72 346 kWh = 170 kWh Cost of electricity = energy transferred cost per unit 19.72 = 170 kWh cost per unit 1972/170 p/kWh = cost per unit Cost per unit= 11.6p/kWh 72643 kWh 72615 </li> <li> Slide 10 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters If the cost of electricity for the period shown on the meters below is 20.80 and the cost per unit is 10.4p, calculate the meter reading shown on the first electricity meter. Cost of electricity= energy transferred cost per unit 20.80= energy transferred 10.4p/kWh 2080p= energy transferred 10.4p/kWh 2080 10.4 kWh = energy transferred energy transferred= 200 kWh = 200 units Meter reading = 84 324 200 = 84 124 ????? kWh 84423 </li> <li> Slide 11 </li> <li> Oxford University Press 2011 IP1.15.5 Electricity meters Look at the two meter readings below. These meter readings were taken at the beginning and end of a three month period. If the first 250 kWh are charged at 15.7p and the remainder at 10.2p, calculate the total cost for the period. Total energy transferred= 93 092 kWh 92 645 kWh = 447 kWh Cost of electricity= energy transferred cost per unit Cost of electricity= (250 kWh 15.7p/kWh) + ((447 kWh 250 kWh) 10.2p/kWh) = (250 kWh 15.7p/kWh) + (197 kWh 10.2p/kWh) = 3925p + 2009.4p = 5934.4p = 59.34 92546 kWh 93290 </li> </ul>