1. 1.1 Energy-consuming appliances at home
Input and output
Main sources of energy in Hong Kong
Energy efficiency
Check-point 1 1 2
Book E3 Section 1.1 Energy-consuming appliances at home

2. Book E3 Section 1.1 Energy-consuming appliances at home
Input and output
Does a rice cooker of power 450 W work at this rate?
Unfortunately, this is only the power input. The actually power output is much less than this value.
When you buy an electrical appliance, will you consider its efficiency?
Book E3 Section 1.1 Energy-consuming appliances at home

3. 1 Main sources of energy in Hong Kong
Electricity is the main source of energy.
 covers 50% of energy needs in Hong Kong
 powers all sorts of appliances at home
Gas (LPG or town gas)
 2nd most popular source of energy in the home
 mainly for cooking and water heaters
Book E3 Section 1.1 Energy-consuming appliances at home

4. Book E3 Section 1.1 Energy-consuming appliances at home
2 Energy efficiency
a Energy conservation
When we use electrical appliances, many different energy conversions occur.
e.g. Turn on a television
light energy, sound energy and heat
electrical energy
Book E3 Section 1.1 Energy-consuming appliances at home

5. Book E3 Section 1.1 Energy-consuming appliances at home
2 Energy efficiency
a Energy conservation
When we use electrical appliances, many different energy conversions occur.
e.g. Turn on a fan
electrical energy
kinetic energy and heat
A lot of electrical appliances generate heat but…
heat is not always the form of energy that we want.
Book E3 Section 1.1 Energy-consuming appliances at home

6. Book E3 Section 1.1 Energy-consuming appliances at home
2 Energy efficiency
b End-use energy efficiency
End-use energy efficiency:
The useful proportion of energy used
End-use energy efficiency
useful energy output
energy input =
 100%
A high-efficiency appliance uses less energy to do the same job.
Example 1
End-use energy efficiency of a kettle
Book E3 Section 1.1 Energy-consuming appliances at home

7. Book E3 Section 1.1 Energy-consuming appliances at home
2 Energy efficiency
c Overall energy efficiency
End-use energy efficiency only tells the energy lost in operating an electrical appliance.
How about the energy lost during generation and transmission of electricity?
initial energy input
power plant
power transmission
appliance
initial energy output
waste heat
Book E3 Section 1.1 Energy-consuming appliances at home

8. Book E3 Section 1.1 Energy-consuming appliances at home
2 Energy efficiency
c Overall energy efficiency
Overall energy efficiency:
Takes the efficiency of each step into account
Overall energy efficiency
final energy output
initial energy input
=  100%
In Hong Kong, the efficiency of
a power station: 34%–53%
transmission: ~95%
Example 2
Overall energy efficiency
Book E3 Section 1.1 Energy-consuming appliances at home

9. Book E3 Section 1.1 Energy-consuming appliances at home
Check-point 1 – Q1
Which form(s) of energy is electrical energy converted into when you use a power drill?
A Kinetic
B Sound
C Heat
D All of the above
Book E3 Section 1.1 Energy-consuming appliances at home

10. Book E3 Section 1.1 Energy-consuming appliances at home
Check-point 1 – Q2
End-use energy efficiency of a kettle = 93%
If its useful output power is 1600 W, what is its input power?
A W
B W
C W
D W
Book E3 Section 1.1 Energy-consuming appliances at home

11. Book E3 Section 1.1 Energy-consuming appliances at home
Check-point 1 – Q3
Efficiency of a power station = 40%
Efficiency of the transmission network = 90%
Efficiency of an electric iron = 60%
Overall energy efficiency = ?
Overall energy efficiency
= 40%  90%  60%
= 21.6%
Book E3 Section 1.1 Energy-consuming appliances at home

12. Book E3 Section 1.1 Energy-consuming appliances at home
The End
Book E3 Section 1.1 Energy-consuming appliances at home