Uss module 4 chpt 5 Sources of Electricity

Module 4:Gadgets Work Wonders (II)Chapter 5 Sources Of Electricity

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Chapter 5 Sources Of Electricity5.1 How is electricity

generated and transmitted? 5.2 What are transformers used

for? 5.3 Why are batteries an important

source of energy?


ObjectivesOutline 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 StationsPower stations are building complexes

where electricity is generated. They are usually described by the energy source they use.


different types of power stations run ondifferent 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. © Copyright Star Publishing

Pte Ltd

Singapore’s existing and plannedpower 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. © Copyright Star Publishing

Pte Ltd

a nuclear power station

Generator in a power stationIn 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 firedpower station

Activity Book LinkActivity 5.1Singapore ElectricityMarket Structure

Energy conversions in a fossil-fuel power station


A coal-fired power station


Activity Book LinkActivity 5.2Generating Electricity

Transmission of ElectricityAfter 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 ElectricityTo 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 electricalenergy 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 machineconverts electrical energy to

mechanical energy

during charging of battery, electrical energy is converted to

chemical potential energy stored in the battery

Chapter 5 Sources Of Electricity5.1 How is electricity generated

and transmitted? 5.2 What are transformers

used for? 5.3 Why are batteries an important

source of energy?


ObjectivesDescribe 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

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Step-up and step-down transformersA 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


TransformersTransformers 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.


TransformersOne 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 LinkActivity 5.3Transformers Used in Daily Life

Chapter 5 Sources Of Electricity5.1 How is electricity generated

and transmitted? 5.2 What are transformers used

for? 5.3 Why are batteries an

important source of energy?


ObjectivesState the importance of batteries

as a source of electricity, giving some examples of their use


Electricity from BatteriesBatteries 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

Electricity from Batteries 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

Electricity from Batteries 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 batteryActivity Book LinkActivity 5.4Batteries


Uss module 4 chpt 5 Sources of Electricity

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