power
TRANSCRIPT
James Watt (1736-James Watt (1736-
1819)1819)
13 April 2023
SLO9: Calculate Power Usage
All electrical appliances transfer energy. The power of an appliance is the amount of energy that it transfers every second.
Power = Current x Voltage(Watts, W) (Amps, A) (Volts, V)
Or P = I V
P = IV
Mr Maude’s Grandma:(the very powerful) Ivy Watts
Power
Watt is the power of the light bulb? I=2A, V=12V
P =I V
=212
=24W
Watt is the power of the hair drier? I=3.5A, V=240V
P =I V
=3.5 240
=840WP
I VP
I V
PI V
P I V=
PI V
PI
V=
PI V
PI
V =
One piece of information is missing from these stickers, use the power formula to calculate the missing value
PI V
PI V
2
1
3
4
5
6
7
8
9
10
11
12
Appliance Voltage / V Current / A Power / W
Extra activity: School Cert. P 197, Q3, 4, 6, 7
1.Mitsubishi TV 230 88
2.Breadmaker 240 650
3.Sony PC Adapter 16 4
4.Data Projector 240 1
5.Kettle 220 2200
6.Telephone 9 0.080
7.Alarm Clock 240 6
8.Toshiba PC 15 4
9.Palm adapter 5 1
10.Toaster 240 800
11.TDK speakers 240 25
12.Goldair Heater 240 2400
0.38
2.71
64
240
10
0.72
0.025
60
5
3.33
0.10
10
Appliance Voltage / V Current / A Power / W
Extra activity: School Cert. P 197, Q3, 4, 6, 7
1.Mitsubishi TV 230 88
2.Breadmaker 240 650
3.Sony PC Adapter 16 4
4.Data Projector 240 1
5.Kettle 220 2200
6.Telephone 9 0.080
7.Alarm Clock 240 6
8.Toshiba PC 15 4
9.Palm adapter 5 1
10.Toaster 240 800
11.TDK speakers 240 25
12.Goldair Heater 240 2400
0.38
2.71
64
240
10
0.72
0.025
60
5
3.33
0.10
10
Power and Energy
Electricity companies charge customers for the electrical energy they use. The amount you pay will depend on 3 things:
1.What appliances you use
2.How long you use them for
3.How much a Unit of electricity costs
The power of the appliance changes how much energy is transferred each second.
The more seconds you use an appliance, the more energy is transferred.
Electricity companies charge per kilowatt-hour, the amount of energy that a 1 kW appliances transfers in 1 hour.
Power and Energy
Energy is the product of power and time:
Energy = Power Time(Joules, J) (Watts, W) (Seconds, s)
Or E = P t
EP t
If the light bulb is left on for 20 seconds how much energy does it transfer?
E =P t
=24 20
=480J
If the hair drier is left on for 5 minutes how much energy does it transfer?
E =P t
=840(560)
=252000J
=252kJ (1kJ = 1000J)
24W
840W
EP t
EP t
EP t
EP t
40W
2 hours2.4 kW
4.5 hours
960W
4 minutes
840W
6 minutes
60W
35 seconds
Calculate the Energy transferred by these appliances. Remember to convert time into seconds and power in Watts
Appliance Energy transferred / J
Toaster
Lamp
Heater
Light bulb
Hairdrier