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 kilowatts10 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 – small2. 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 used1. If we leave lights on for a long time we will

use up more energy than for a shorter time.2. A kettle transfers 3 000 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 = Power x timeWe have used2. Joules = Watts x

secondsNow we have3. kWh = kW x hours

Working out the kWh - 1

How much does it cost to run a 5kW heater for 10 hours?

1. kWh used = 5 x 10 = 502. 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 1000

1. 60 W = 60/1000kW = 0.062. kWh used = 0.06 x 20 = 1.2 kWh3. Cost = 1.2 x 5 = 6.0 halalah

Electrical powerDevice Power

(W)Power (kW)

Time on in a month(h

Energy used (kWh)