Connect the appliance to the
power rating using an arrow!
Appliance
Kettle
Iron
Power rating (W)
1100W
65W
Television
1800W
Hair dryer
2000W
Were
you
correct?
Appliance
Power Rating
Kettle
2000 W
Iron
1100 W
Television
65 W
Hairdryer
1800 W
Kilowatt Hours (kWh)
electrical energy used = power x time
• 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,
1 unit of electricity = 1 kilowatt hour
For example
Drill 5kW on
for 2 hours!
1kW costs 10p
1. Energy used = Power x time
2. Total cost= number of kilowatt hours x
cost per kilowatt hour
Energy used = 5kW x 2hours
Energy 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
Power in Time
Number of units
in watts kilowatt used
used
(W)
(kW)
(hours)
Kettle
2000
2
1
Energy = Power x time 2 x 10p =
Energy = 2 x 1 = 2kwh 20p
Drill
5000
5
2
Energy = 5 x 2 = 10
Phone
charger
Normal
Light bulb
TV
Hairdryer
Total cost
10 x 10p =
£1.00
Answers
Device
Power
Power in Time
Number of units
in watts kilowatt used
used
(W)
(kW)
(hours)
Kettle
2000
2
1
Energy = Power x time 2 x 10p =
Energy = 2 x 1 = 2kwh 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
0.5
3
Energy = 0.5 x 3= 1.5
1.5 x 10p =
15 p
1.5kW
0.5
Energy = 1.5 x 0.5 =
0.75
0.75 x 10p
= 7.5p
500W
Hairdryer 1500
Total cost
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 = 0.5kWh
0.5kWh x 12p = 6p
6p x 365 days = 2190p = £21.90
• To run a 15W eco bulb for 5 hours a day all year costs:
15W x 5hours = 75Wh = 0.075kWh
0.075kWh x 12p = 0.9p
0.9p 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
2
1
1
3
2
8
3
2
How many units of electricity had been used
by this family?
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