Transcript File

Sustainable Energy
Lesson 5
Learning objective: To explain the link
between the power rating and energy use
of an electrical appliance.
• Must: Recall the definition for power and give its
unit of measurement – Grade D
• Should: Be able to calculate power rating and
energy used by an electrical appliance. - Grade C
• Could: Calculate the power of a range of
appliances using an ammeter and a voltmeter –
Grade B.
• Keywords: Power, current, voltage, watt and
energy transfer.
Starter-Label the power station
How many did you get?
• 1. Furnace and
boiler.
• 2. Turbine.
• 3. Generator.
• 4. Transformer.
Mains supply.
• What is the mains
supply voltage to our
homes?
• 230 V (volts).
• You need to
remember this.
Do different appliances use different
amounts of electricity?
Joules
• Energy is measured in Joules (J)
• We need to know how much energy something uses
over time = a rate
• We can use Joules per second (J/s)
• 1 Joule / sec = 1 Watt (W)
A 100W light bulb uses 100J of energy every second
Power
When an electric current is passed through a
device electric current is transferred from the
supply to the device.
The rate at which this energy is transferred is called
POWER.
Power is measured in WATTS (W).
Power Rating
• Different electrical devices have different power ratings
• They use different amounts of electrical energy over a
given time.
VS
15W
100W
P=IxV
Power (Watts) = Current (amps) x Voltage (volts)
Voltage = Potential Difference
Pee on the Ivy
P
=
I
x
V
Possible homework task
Task- Complete the table using the equation P=IV
Appliance
Power (w)
Voltage (v)
Kettle
3000
Toaster
1550
230
Microwave
1300
240
Drill
Door Lift
2300
15
TV
59
Vacuum Cleaner
1.5
10
230
CD player
Hairdryer
13.0
240
Fax Machine
Current (A)
1.0
0.06
230
240
800
2.7
3.5
Desk Lamp
12
4.2
Sewing Machine
230
0.17
Task- Complete the table using the equation P=IV
Appliance
Power (w)
Voltage (v)
Current (A)
Kettle
3000
230
13.0
Toaster
1550
230
6.7
Microwave
1300
240
5.4
Drill
360
240
1.5
Door Lift
2300
230
10
Fax Machine
230
230
1.0
CD player
15
250
0.06
TV
59
230
0.26
Vacuum Cleaner
648
240
2.7
Hairdryer
800
229
3.5
Desk Lamp
50
12
4.2
Sewing Machine
39
230
0.17
The Watt
1 Watt = 1 Joule transferred in 1 second
Power (W)= Energy (J) / Time (s)
Device
Kettle
Power Rating
(Watt)
2400
Time (sec)
180
Energy = Power x Time
Energy = 2400W x (180s)
Energy = 432000J
Energy (J)
432000
Electric Cooker: 10kW
Fridge: 50W
Freezer: 300W
Washing machine: 500W
Dishwasher: 1300W
Electric Cooker: 10kW. 45mins
Fridge: 50W. 24hours
Freezer: 300W. 24hours
Washing machine: 500W. 1 hour
Dishwasher: 1300W. 45mins
Device
Power Rating
(Watt)
Time (sec)
Energy (J)
Electric
Cooker
Fridge
10000
2700
27000000
50
86400
4320000
Freezer
300
86400
25920000
Washing
Machine
500
3600
1800000
Dishwasher
1300
2700
3510000
Total energy use in one day:
63036000J or
63 million and 36 thousand Joules
and Total Energy for 3 months:
5673240000J or
5 billion, 6 hundred and seventy three million, 2
hundred and forty thousand Joules!
Plenary- True or False
1.
2.
3.
4.
5.
6.
7.
8.
Power is measured in watts?
Power= voltage / current?
Current is measured in volts?
Voltage is measured in volts?
Potential difference is another word for voltage?
I is the symbol for current?
The mains supply voltage to our homes is 240V?
The higher the power rating the more energy is
used?
9. 10 watts means 10 joules of energy every minute?