Electrical energy consumption

1. Section 9 Electrical energy consumption

2. Lighting 100 Watts 60 Watts 40 Watts

3. Heating 2 kilowatts 750 Watts

4. In the kitchen 800 Watts 3 kilowatts

5. Entertainment 500 Watts

6. Washing 10 kilowatts 4 kilowatts

7. Cleaning 700 Watts

9. Paying for electricity We pay for the Energy we consume

10. Electrical energy meter • This is a domestic energy meter • Note the units of energy • Not the Joule! • The kWh – the kilowatt-hour.

12. Units of energy • Joules - J – small • Kilowatt hours – kWh – large Electricity suppliers use the kWh sometimes called THE UNIT

15. Electricity bill

16. The cost of electrical energy • We pay for the energy we use • The meter is read usually every 1 month • The meter reads the kiloWatts hours of energy used • End reading – start reading = kWh used • Each kWh has a cost – about 5-26 halalah • The total energy cost is calculated from this • Sometimes a fixed standing charge is added on

17. The energy used • If we leave lights on for a long time we will use up more energy than for a shorter time. • A kettle transfers 3 000 J of energy every second – this is its power. • A lamp transfers 60 J every second – this is its power. • The energy used depends on the Power of the device and the time it is left on.

18. Calculating the kWh of energy used The number of kWh of energy use can be calculated. • Energy = Power x time We have used • Joules = Watts x seconds Now we have • kWh = kW x hours

19. Working out the kWh - 1 How much does it cost to run a 5kW heater for 10 hours? • kWh used = 5 x 10 = 50 • Cost = 50x 5 halalah = 250 halalah=SR2.50

20. Working out the kWh - 2 How much does it cost to run a 60W lamp for 20 hours? First you must convert W into kW by dividing by 1000 • 60 W = 60/1000kW = 0.06 • kWh used = 0.06 x 20 = 1.2 kWh • Cost = 1.2 x 5 = 6.0 halalah

21. Electrical power