Electrical energy consumption Section 9

Lighting 40 Watts 100 Watts 60 Watts

Heating 750 Watts 2 kilowatts

In the kitchen 3 kilowatts 800 Watts

Entertainment 500 Watts

Washing 4 kilowatts 10 kilowatts

Cleaning 700 Watts

Paying for electricity We pay for the Energy we consume

Electrical energy meter 1.This is a domestic energy meter 2.Note the units of energy Not the Joule! The kWh – the kilowatt-hour.

Units of energy 1.Joules - J – small 2.Kilowatt hours – kWh – large Electricity suppliers use the kWh sometimes called THE UNIT

Electricity bill

The cost of electrical energy 1.We pay for the energy we use 2.The meter is read usually every 1 month 3.The meter reads the kiloWatts hours of energy used 4.End reading – start reading = kWh used 5.Each kWh has a cost – about 5-26 halalah 6.The total energy cost is calculated from this 7.Sometimes a fixed standing charge is added on

The energy used 1.If we leave lights on for a long time we will use up more energy than for a shorter time. 2.A kettle transfers J of energy every second – this is its power. 3.A lamp transfers 60 J every second – this is its power. 4.The energy used depends on the Power of the device and the time it is left on.

Calculating the kWh of energy used The number of kWh of energy use can be calculated. 1.Energy = Powerx time We have used 2.Joules= Wattsxseconds Now we have 3.kWh= kWxhours

Working out the kWh - 1 How much does it cost to run a 5kW heater for 10 hours? 1.kWh used = 5 x 10 = 50 2.Cost= 50x 5 halalah = 250 halalah =SR2.50

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 W = 60/1000kW = kWh used = 0.06 x 20 = 1.2 kWh 3.Cost= 1.2 x 5 = 6.0 halalah

Electrical power DevicePower (W) Power (kW) Time on in a month(h Energy used (kWh)