Connect the appliance to the power rating using an arrow!

Appliance

Kettle

Iron

Television

Hair dryer

Power rating (W)

1100W

65W

1800W

2000W

Appliance Power Rating

Kettle 2000 W

Iron1100 W

Television 65 W

Hairdryer 1800 W

Were you

correct?

Kilowatt Hours (kWh)

• 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,

electrical energy used = power x time

1 unit of electricity = 1 kilowatt hour

For example Drill 5kW on for 2 hours!

1kW costs 10p

1. Energy used = Power x time2. Total cost= number of kilowatt hours

x cost per kilowatt hour

Energy used = 5kW x 2hoursEnergy 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 in watts (W)

Power in kilowatt(kW)

Time used (hours)

Number of units used

Total cost

Kettle 2000 2 1 Energy = Power x timeEnergy = 2 x 1 = 2kwh

2 x 10p = 20p

Drill 5000 5 2 Energy = 5 x 2 = 10 10 x 10p = £1.00

Phone charger

Normal Light bulb

TV

Hairdryer

AnswersDevice Power

in watts (W)

Power in kilowatt(kW)

Time used (hours)

Number of units used

Total cost

Kettle 2000 2 1 Energy = Power x timeEnergy = 2 x 1 = 2kwh

2 x 10p = 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 500W 0.5 3 Energy = 0.5 x 3= 1.5

1.5 x 10p = 15 p

Hairdryer

1500 1.5kW 0.5 Energy = 1.5 x 0.5 = 0.75

0.75 x 10p = 7.5p

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 = 0.5kWh0.5kWh x 12p = 6p6p x 365 days = 2190p = £21.90

• To run a 15W eco bulb for 5 hours a day all year costs:15W x 5hours = 75Wh = 0.075kWh0.075kWh x 12p = 0.9p0.9p 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

How many units of electricity had been used by this family?

2 1 1 3 2 8 3 2

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