Uss module 4 chpt 5 Sources of Electricity

Module 4:
Gadgets Work Wonders (II)
Chapter 5 Sources Of Electricity
1© Copyright Star Publishing Pte Ltd

Chapter 5 Sources Of
Electricity
5.1 How is electricity generated and
transmitted?
5.2 What are transformers used for?
5.3 Why are batteries an important
source of energy?

Objectives
 Outline the processes that produce
electricity from fossil fuels to
transmitting electricity to the homes
and consume electricity in common
household electrical appliances (in
terms of conversions of energy)
 Understand that electricity is
transmitted from a power station
through a grid of high voltage
transmission lines

Power Stations
 Power stations are building complexes
where electricity is generated. They
are usually described by the energy
source they use.
© Copyright Star Publishing Pte Ltd 4
different types of power stations run on
different energy sources

Fossil-fuel power stations
 Together, gas-fired, oil-fired and coal-fired
power stations are known as fossil-fuel power
stations. This is because their sources of
energy (natural gas, oil and coal) are all fossil
fuels.
a gas-fired power station

Fossil-fuel power stations
 In fossil-fuel power stations, the fuels are burnt
to produce heat. This burning process will
produce air pollutants. Of the three types of
fossil fuels, natural gas is the cleanest while
coal produces the largest amount of
pollutants.
an oil-fired power station a coal-fired power station

Power stations in Singapore
 Presently, the power stations in Singapore are either
oil-fired or gas-fired.
 The power stations play an important role of supplying
electrical energy for daily uses and to sustain our
economy.
Singapore’s existing and planned
power stations

Nuclear power stations
 Nuclear power stations use
energy provided by nuclear fuels
to generate electricity.
 They produce very little
pollutants but exposure to
nuclear fuels can cause nuclear
burns, cancer and deformed
offsprings.
 Great care must be taken to
prevent nuclear sources from
leaking out.
 However, accidents and natural
disasters can break down the
protection structures and
cause nuclear leakage.
a nuclear power station

Generator in a power station
 In both fossil-fuel power stations and
nuclear power stations, the central piece
of equipment is the generator. When the
generator is turned, electricity will be
produced.
generator in a fossil-fuel fired
power station
Activity Book Link
Activity 5.1
Singapore Electricity
Market Structure

Energy conversions in a fossil-fuel
power station

A coal-fired power station
Activity Book Link
Activity 5.2
Generating Electricity

Transmission of Electricity
 After electricity is
generated, it is
transmitted from the
power stations to homes
and offices using long
cables through an
electricity grid. An
electricity grid is a
network of electrical
cables and electrical
substations.
 In Singapore, most
transmission cables are
underground.
overhead transmission cables

Transmission of Electricity
 To reduce energy lost during
transmission, electricity is stepped up
to a high voltage before transmission.
 At substations near offices and
homes, voltage will be stepped down
to around 230 V. Stepping up and
down of voltages are done using
transformers.

Using Electrical Appliances
 When we use the
electrical appliances
at home, the
electrical energy is
converted to other
forms of energy.
a bulb converts electrical
energy to light and heat energy

Using Electrical Appliances
a kettle converts electrical
energy to heat energy
a television converts electrical energy
to light and sound energy
a washing machine
converts electrical energy to
mechanical energy
during charging of battery, electrical
energy is converted to chemical potential
energy stored in the battery

Electricity
transmitted?
source of energy?

Objectives
 Describe a transformer as two coils of
wire wound onto a core of iron
 Understand the use of step-up and
step-down transformers and give
examples of their use (including high
voltage transmission of electricity)

Transformers
 The label found at the back of the laptop computer
shows that the laptop should be used with a 19 V
supply.
 However, the mains supply is 230 V.
 The transformer in the adaptor changes the voltage
of the mains to a lower voltage.

Transformers
 A transformer is an electrical device that changes
the voltage of an alternating current (a.c.) supply.
 Transformers come in different types and sizes from
small ones in laptop adaptors to huge ones at power
stations.
large transformers are used
at power stations

Transformers
 A simple transformer consists of two coils of wire
wound on an iron core.
 One coil is called the primary coil and the other coil is
called the secondary coil.
 The input voltage is connected to the primary coil and
the output voltage is obtained at the secondary coil.
a simple transformer
€
€
€

Step-up and step-down transformers
 A transformer that increases the
voltage is called a step-up
transformer while a transformer that
decreases the voltage is a step-down
transformer.

Step-up and step-down
transformers
A step-down
transformer has
more turns at
the primary coil.
A step-up
transformer has
more turns at the
secondary coil

Transformers
 Transformers work only with alternating
current (a.c.) which changes direction
many times in one second.
 Transformers cannot work with direct
current (d.c.) which flows in one direction.
 The working of transformer is based on the
principles of electromagnetism.

Transformers
 One important use of transformers is to step-up
voltage of electricity at power stations before
the electricity is transmitted through cables.
 The voltage of the electricity is then stepped
down at substations near homes and offices.
 Although it may seem troublesome and
unnecessary, this process of stepping up and
stepping down reduces a lot of energy loss
during transmission.
Activity Book Link
Activity 5.3
Transformers Used in Daily
Life

Electricity
transmitted?
source of energy?

Objectives
 State the importance of batteries as a
source of electricity, giving some
examples of their use

Electricity from Batteries
 Batteries are a
portable source of
electrical energy.
 Some batteries
come in standard
sizes (e.g. AA size)
while others are
designed to be
used with specific
gadgets.
standard size
batteries
laptop batteries
a car battery

 The production of electricity using
batteries involves energy
conversion.
 The chemical energy stored in the
chemicals in the batteries is
converted to electrical energy.
 All batteries have 2 terminals,
positive (+) and negative (–).
 When connected to a circuit, current
will flow out from the positive (+)
terminal and return to the battery
through the negative (–) terminal.
each battery has
a ‘+’ and a
‘–’ terminal

 When all the chemical
energy in a battery is
converted, the battery
can no longer supply
electrical energy.
(a) If the battery is non-
rechargeable,
it has to be thrown
away properly.
(b) If the battery is
rechargeable, it can
be used again.
during recharging, electrical
energy from the mains is
converted to chemical
energy stored in the battery
Activity Book Link
Activity 5.4
Batteries

Uss module 4 chpt 5 Sources of Electricity

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