Information systems - NSW Department of Education

Transcription

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Senior Science
HSC Course
Stage 6
Information systems
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SSCHSC43170
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P0025973
Number: 43170
Title: Information systems
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Text of interview with scientist Sue Spaargaren, (accessed November, 2000) found at
http://www.swimwithdragons.com.au/cgibin/cgi.../allegro.pl?wis_search.Sue+Spaargaren
Part 6 pp 19-22
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Copyright Regulations 1969
WARNING
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New South Wales Department of Education and Training
(Centre for Learning Innovation)
pursuant to Part VB of the Copyright Act 1968 (the Act).
The material in this communication may be subject to copyright under the Act.
Any further reproduction or communication of this material by you may be the
subject of copyright protection under the Act.
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.
Published by
Centre for Learning Innovation (CLI)
51 Wentworth Rd
Strathfield NSW 2135
_______________________________________________________________________________________________
_
Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or
transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the
written authority of the Centre for Learning Innovation (CLI).
© State of New South Wales, Department of Education and Training 2007.
Contents
Module overview ........................................................................ ii
Resources............................................................................................ iii
Icons .................................................................................................... iv
Glossary................................................................................................v
Part 1: Get the message? ...................................................1–34
Part 2: Waves waves waves ...............................................1–30
Part 3: More waves .............................................................1–23
Part 4: Messages from space..............................................1–26
Part 5: Information through impulse ....................................1–20
Part 6: Fibre optics ..............................................................1–34
Student evaluation of module
Introduction
i
Module overview
Welcome to the Information systems module for the HSC component of
the Senior Science course.
This module explains how mobile phones, radios, telephones, televisions,
satellites and satellite dishes work.
You will understand how energy is transformed so that information can
be transmitted from one place to another. Many information systems rely
on digital transmissions of light, radio waves or microwaves using
electricity.
The importance of the electromagnetic spectrum for information
transmission is addressed as is the difference between AM, FM and
microwave communication.
You will appreciate the purposes of different satellite orbits and identify
the type of satellites used for live telecast.
Studying how a fax machine works will enable you to better understand
how information can be transmitted in the form of electrical impulses.
Finally you will explore the properties of optical fibres using light and
appreciate how they transmit information in telecommunications using
infra–red radiation.
Even if you are a technophobe, you should enjoy Information systems
and appreciate the advances in technology that now allow us to
communicate across the globe.
ii
Information systems
Resources
You will need the following equipment to carry out activities and
experiments during the module. In most cases, you should have most of
the items listed around your home.
Part 1
Part 5
•
Information systems audiotape
or access to the internet audio
files
•
•
scissors
Part 2
•
coloured pencils
•
glue
Part 3
•
household items with bar
codes
•
string instrument or a rubber
band
•
portable radio receiver with
AM and FM
Information systems audiotape
or access to the internet audio
files
Part 6
•
•
torch
hammer
•
sticky tape
•
dark tea towel or hand towel
•
two nails of different
thicknesses
Part 4
Introduction
•
toothpicks
•
round piece of fruit
•
small object such as a raisin or
ball of blutack
•
small amount of blutack or
plasticine
iii
Icons
The following icons are used within this module. The meaning of each is
written beside it:
The hand icon means there is an activity for you to do. It may be
an experiment or you may make something.
The talk icon guides you to discuss a topic with others.
There are exercises at the end of each part for you to complete
and send to your teacher.
The headphone icon asks you to complete an activity while
listening to an audiotape.
The safety icon points out that care needs to be taken when
carrying out a task.
There are suggested answers for the following questions at the
end of each part.
This icon suggests you watch a video.
iv
Information systems
Glossary
The following glossary provides the scientific meaning for many of the
term used in this module, Information systems.
The HSC examiner will expect you to understand the meaning of every
scientific term used. If you find a term that you do not understand, then
look it up in a scientific dictionary or ask your teacher for assistance.
Introduction
aerial
device for transmitting and/or receiving
radio waves
amplitude modulated
(AM)
the height of a carrier radio wave is
modified to carry broadcast information;
AM radio waves
analog
information not coded as ons or offs or
zeros and ones
antenna
metal wire which detects radio waves
bandwidth
the range of frequencies over which an
electromagnetic wave is transmitted
bar code
series of black and white lines containing
code information representing the
manufacturing country, the manufacturer
and the item code
boosting
using electricity to enhance a signal for
better volume and clarity
cathode ray tube
vacuum sealed space where a beam of
electrons is fired at a screen coated with
phosphor
cladding
in terms of optical fibres; the material
coating the optical fibre which is less
optically dense than the core of the optical
fibre
code
a collection of symbols or words used for
communication
coder
transforms information into a specific
code
communication system
information transfer system
compact disc (CD)
thin reflective metallic disc with tiny bits
containing information for computers
and/or stereos such as computer programs
or music
compact disc player
device for changing compact disc
information into sound
v
vi
compression
part of a sound wave where the particles
of matter are closest together
constellation
(in terms of satellites) a constellation is a
series of satellites which together provide
data cover of particular parts of the Earth
crest
the highest point of a wave equal to the
densest part of a sound wave compression
critical angle
the incident angle at which a beam of light
will travel along the edge of an optically
denser medium
decoder
transforms coded information into another
form
demodulator
removes the carrier wave from the radio
signal
diaphragm
vibrating membrane in microphone or
speaker
digital
on and off signals or zero and one
impulses which carry information
digitised
information transferred as a series of ons
or offs or zeros and ones
downlink
electromagnetic waves transmitted from a
satellite to Earth; this transmission may be
at a different frequency than the uplink
electromagnetic spectrum
(EMS)
electromagnetic waves arranged in order
of increasing energy/increasing
frequency/decreasing wavelength
electromagnetic waves
energy carrying transverse waves that are
part of the electromagnetic spectrum that
does not require matter to carry the energy
electronic
using electricity usually passing through
solid state components
electrons
negatively charged particles; the flow of
electrons is electricity
elliptical orbit
orbit around a central body like the Earth
that is closer on one side than the other
email
computer based communication using
telecommunication lines
encryption
conversion of easily understood
information into symbols so that the
information is protected and cannot be
understood by others
Information systems
Introduction
fax (facsimile) machine
optically scans information on sheets of
paper, converting them to digital messages
for decoding and printing by another fax
machine
fibre optics
passing of light through fibre by internal
reflection either to transmit light or images
in medical technology or to communicate
in information transfer systems
footprint
(in terms of satellites) the area of the Earth
a satellite is calibrated to cover for
receiving or transmitting information
frequency
the number of waves to pass a point in one
second
frequency modulated (FM)
the frequency of a carrier radio wave is
modified to carry broadcast information
geostationary satellite
satellite held in a fixed position in orbit
above the Earth
graded optical fibre
optical fibres which are more optically
dense towards the centre and less optically
dense towards the edge of the fibre
hertz (Hz)
measurement of frequency; the number of
waves to pass a point in one second
high Earth orbit
geostationary satellites are placed in high
Earth orbit 36 000 km above the Earth’s
surface
impulse
short burst of energy
incident angle
the angle between the normal and the
entering light beam
information (transfer) system
way of transferring information
(meaningful data) from place to place that
uses energy
infra–red
waves of the electromagnetic spectrum
with wavelengths ranging from 700 nm to
1 mm
Internet
worldwide computer networks linked
through telecommunication lines and
ionosphere
ionised region of the atmosphere
extending to about 1000 km above the
Earth's surface able to reflect radio waves
kinetic energy
movement energy
land connected telephones
telephones connected by landlines
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landline
wires or cables used as communication
links running above or below ground
larynx
voice box containing vocal cords
line of sight
unimpeded view between two points such
as a transmitter and receiver
longitudinal
waves that compress particles of matter,
transferring energy in the same direction
as the wave movement
low Earth orbit
satellite orbit about 1000 km or less from
Earth
magnetic strip
strip on credit cards, key cards and travel
tickets containing magnetically aligned
digital information
mechanical waves
waves that require a medium for
transmission
medium Earth orbit
satellite orbit about 10 000 km from Earth
megahertz
millions of hertz
micrometre
one millionth of a metre
microwaves
part of the electromagnetic spectrum from
1 mm to 30 cm in wavelength
mobile phone
telephone using microwave transmissions
for communication between transmitting
towers and mobile telephones
modem
abbreviation for moulator–demodulator;
device that changes digital signals from
computer to analog signals that travel
through copper wires; also changes analog
signals to digital so they can enter a
computer
modulation
adjustment of an electromagnetic wave so
that it carries information
multimode optic fibre
optic fibre, the thickness of a strand of
hair through which thousands of different
digital transmissions may be sent
nanometre
one billionth of a metre
non–electronic
without the use of electricity
non–verbal
without the use of words (spoken or
written or signed)
normal
(in terms of optics) perpendicular to the
surface of the interface between two
mediums
Information systems
Introduction
optical/optically
involving light energy
optical fibres
a strand of material (commonly glass
fibre) through which light can travel
orbit
an object rotating around another object in
space due to the gravitational pull of the
object with greater mass
order of magnitude
measurement of size that uses powers of
ten; two quantities of the same order of
magnitude have different but similar sizes
photodiode
light sensitive diode that produces an
electrical output on exposure to light
polarising
(with regards to electromagnetic waves)
limiting the plane of the electromagnetic
wave by eliminating waves in other planes
polyurethane
(in terms of fibre optics) a waterproof
coating of an optical fibre
radio (receiver)
device which tunes into specific AM and
FM radio waves for information
transmission
radio frequency amplifier
boosts selected radio frequencies
radio telescope
large dish–shaped object to reflect radio
waves to a central receiver; moveable to
receive waves from specific co–ordinates
in space
random access memory
(RAM)
where information is temporarily held
electrically in a computer’s memory
rarefaction
part of a wave where the particles of
matter are furthest apart
receiving dish
dish–shaped object that collects then
reflects electromagnetic waves to a central
point for collection
refractive index
measure of ability of a material to bend
light; the higher the refractive index the
more bending of light occurs and the more
likely it is that total internal reflection
occurs
satellite
object held in orbit around a body such as
a planet due to gravity
satellite dish
reflects electromagnetic waves to a
receiver
short waves (SW)
AM radio waves of short wavelength and
high frequency that are reflected by the
ionosphere and Earth and so used for
overseas broadcasts
ix
x
silicone
(in terms of fibre optics) a flexible layer
surrounding an optical fibre and cladding
for protection
small–diameter core
optical fibre with a diameter small enough
to fit only one light impulse at any one
time
sound system
plays music from compact discs, tapes or
the radio
technophobe
person with fear or dislike of modern
technology
telecommunications
any communication involving the use of
connecting lines or electromagnetic waves
over long distance
television (receiver)
cathode ray tube and screen attached to an
aerial for radio wave reception; pictures
appear on the screen due to the cycling of
an electron beam across the screen
total internal reflection
reflection of light off the sides of a denser
medium back inside the denser medium
transmitting tower
tall tower which sends radio waves or
microwaves for communication purposes
transverse
the direction of energy movement is at
right angles to the wave travel direction
trough
the lowest point of a wave equal to the
zone of lowest pressure in a sound wave
tuner
electrical circuit device that selects
specific radio wave frequencies
uplink
electromagnetic waves transmitted to a
satellite from Earth
vacuum
space containing no particles of matter
verbal
using words (spoken or written or sign) as
a code between sender and receiver
video conferencing
teleconferencing using real–time video
images over a monitor
visible light
part of the electromagnetic spectrum
ranging from 700 to 400 nm.
wavelength
the distance from crest to crest or trough
to trough on a wave
Information systems
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Senior Science
HSC Course
Stage 6
Information systems
Part 1: Get the message?
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Senior Science Stage 6 HSC Course
Lifestyle chemistry
Medical technology–bionics
Information systems
•
Get the message?
•
Waves waves waves
•
More waves
•
Messages from space
•
Information through impulse
•
Fibre optics
Option
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Contents
Introduction ............................................................................... 2
Sending messages.................................................................... 4
Energy...................................................................................................5
Information transfer ................................................................... 7
Telecommunications ............................................................................7
Mobile phones .....................................................................................8
Television............................................................................................10
Compact disc players.........................................................................11
Sound system speakers.....................................................................14
Radios.................................................................................................15
Information systems and society ............................................. 16
Advantages of information systems......................................... 18
Summary................................................................................. 20
Appendix ................................................................................. 23
Suggested answers................................................................. 25
Exercises–Part 1 ..................................................................... 31
1
Introduction
In Part 1, you will be given opportunities to learn about the energy
transformations in various information systems, which are responsible
for information transfer. You will be presented with information transfer
processes in mobile phones, telephones, faxes, televisions, sound
systems, CD players and radios and asked to establish a timeline of the
development of these communication systems.
In Part 1, you will be given opportunities to learn to:
•
–
code common to both parties
–
message
–
transmission of coded message
–
decoder
•
identify a range of information systems used daily
•
classify information systems as
–
verbal and non–verbal
–
short distance and long distance
–
electronic and non–electronic
•
recall phenomena and events where different forms of energy are
used
•
identify the transformation of energy at each stage of information
transfer in one of the following devices
•
2
outline the basic pattern of information transfer process as
–
–
mobile phones
–
television
–
radios
–
Compact Disc players
discuss the advantages of using a range of information systems.
Information systems
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In Part 1, you will be given opportunities to:
•
gather and process first–hand and secondary information on the
basic pattern of the information transfer process in one of the
following systems:
–
–
mobile phones
–
television
–
radios
–
Compact Disk players
to outline features that the systems have in common and use
available evidence to discuss the applications of these systems
•
gather and process information from secondary sources to develop a
timeline of communication systems introduced to society and use the
available evidence to analyse the impact these systems have had on
society and predict possible future directions in communication
technologies.
Extracts from Senior Science Stage 6 Syllabus © Board of Studies NSW,
November 2002. The most up–to–date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
3
Sending messages
Have you ever wondered how land connected telephones and mobile
phones work? Do you know how televisions, radios and compact disc
players work?
All of the above technologies have a basic pattern of information
transfer:
•
a code (common both to sender and receiver)
•
a message being sent
•
transmission of the coded message
•
decoding of the message at the receiving end.
If you have heard someone speak in a language you did not understand,
you could not receive the message because you did not have the code
(knowledge of the language) for decoding.
1
a) Remove the Appendix from the back of this part. Cut out the
shaded boxes. You should be left with an A4 sheet of paper with
holes in it. This is a code.
b) Place the Appendix over the top of this page (the page you are
currently reading). The holes in the page should reveal specific
words on this page when the edges are lined up.
c) Write the words below that are revealed by the holes. What is the
message?
_________________________________________________
_________________________________________________
Check your answer before moving on.
Well done. You just decoded a message.
2
What four things are essential for the successful transfer of
information?
______________________________________________________
______________________________________________________
4
Information systems
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3
Many communication systems (information transfer systems) are
used on a daily basis around the world. Seven of these are
mentioned on the previous page. List these information transfer
systems below with any others with which you are familiar.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
The above information transfer systems all use some form of energy.
The following section looks at the different forms of energy and the
energy transformations involved in each information transfer system.
Turn to Exercise 1.1 at the back of this part to classify various information
transfer systems.
Energy
You should remember that energy cannot be created or destroyed, just
changed from one form of energy to another, but do you remember the
different forms of energy?
1
Match the forms of energy below with the type of energy involved by
using a line.
Form of energy
Type of energy
chemical
energy released as traveling vibrations
potential
movement energy
kinetic
energy carried as waves at the speed of light
heat
energy carried by moving electrons
light
energy stored in chemicals
sound
energy from light source
electromagnetic
energy that can be released later
electrical
energy from the Sun
solar
energy from differences in temperature
nuclear
energy released from converting mass into
energy during fission or fusion
Check your answers before moving on.
5
2
3
Knowing that energy can only be changed from one form of energy
to another form of energy (like the ones on the previous page), you
should be able to write down the energies before and after each of
the following scenarios. The first two have been done for you as a
guide.
Scenario
Energy transformation
sound system playing music
electrical
sound
car using fuel
chemical
kinetic
electric light is on
____________
____________
battery use in a walkman
____________
____________
boiling an electric kettle
____________
____________
plants using the sun’s light
____________
____________
heating food in microwave
____________
____________
microwave using electricity
____________
____________
storing the sun’s energy in
batteries
____________
____________
Write three more scenarios and their energy transformations below.
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
The transfer of information in information systems may not be as simple
as changing one form of energy into another. Some information systems
may change one form of energy into several types of energy or change
energy into different forms of energy and back again.
The following section explains the transformation of energy at each stage
of the information transfer process in various information systems.
6
Information systems
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Information transfer
Telecommunications
The Information transfer section of the Information systems audiotape
contains information on the information transfer process used in
telecommunications. Telecommunications involves telephones, mobile
phones, fax communications, paging systems and more.
Listen to the telephone section of the Information systems audiotape or the
telephone internet audio file (at www.lmpc.edu.au/science , go to Senior
Science, go to Information systems, go to info systems audio) to gather
information to complete the following activities on telecommunications.
Land connected telephones
speaker
to telephone lines
hook
switch
microphone
Write the information on the following page in the appropriate places on the
diagram above using the telephone section of the audiotape/internet audio
files. Note that electrical impulses are bursts of electrical energy.
7
•
electrical impulses entering telephone
•
microphone transforms sound energy into kinetic energy of a
diaphragm then electrical energy
•
speaker transforms electrical impulses into kinetic energy of a
diaphragm then sound energy
•
electrical impulses are sent to phone line
•
electrical impulses are converted into light energy or electromagnetic
energy for long distance transmission.
Check your answers.
Mobile phones
Use the mobile phones section of the audiotape/internet audio files to follow
the energy changes in the following diagram then answer the questions on
mobile phones over the page.
sound vibrations
produced in the
larynx – mechanical
energy
microwave converted to
electrical energy then
sent to switching centre
microwave
converted to an
electrical signal
at the cell tower
connecting
wire
sound
energy
electrical signal
converted to
microwave
sound energy
converted to
electrical energy
electrical or
light impulses
sent to
another cell
tower
microwave
microwave is
converted to an
electrical signal
and then to
sound waves
electrical signal converted to
a microwave at the cell tower
sound waves converted
to mechanical energy as
vibrations of the ear drum
Energy transformations involved in mobile phone connections.
8
Information systems
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1
What energy is converted into electrical energy from mobile phone
batteries?
_____________________________________________________
2
What is sound energy from your voice converted to inside a mobile
phone for transmission from the phone to a cell tower?
_____________________________________________________
_____________________________________________________
3
A cell tower boosts a radio wave signal using ___________ energy.
_____________________________________________________
4
After the message is boosted at a cell tower, describe two different
ways the message may be sent to the receiving mobile phone.
_____________________________________________________
_____________________________________________________
_____________________________________________________
5
Explain why digital mobile networks are considered to be an
improvement on analog networks.
_____________________________________________________
_____________________________________________________
Check your answers.
9
Television
Use the television section of the Information systems audiotape/internet audio
files to answer the following questions on how televisions work.
cord attaches to an antenna
television is
attached to
electricity
cathode ray tube
electron beam moves
in lines across the
screen 60 times a
second to create a
picture
television screen
A television consists of a cathode ray tube with a phosphor coated screen.
a) transmitting tower
__________________________________________________
__________________________________________________
b) receiving antenna
__________________________________________________
__________________________________________________
c) cathode ray tube (picture tube)
__________________________________________________
__________________________________________________
d) screen
__________________________________________________
__________________________________________________
10
Information systems
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2
Explain how a single signal can cause an entire picture to appear on
the screen.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
3
Explain the difference between the picture tube televisions and flat
screen televisions and how the images are formed on the screen.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Use the compact disks section of the audiotape or internet audio files to
answer the following questions on compact discs.
1
Label the layers in the cross–section of a compact disc below.
pits that make the bumps on
the other side
1.2 mm
pits are pressed into the
polycarbonate disc
representing a digital signal in
circular tracks
laser light
directed this
way
11
one track
500 nm
1 600 nm
another track
Laser light hits a bump that equals 1 or a no bump which equals 0.
The 1s and 0s are reassembled into numbers and used to reconstruct
the original sound (or picture) signal.
s
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p in
n th e
d ir e ct io n o f t h
eC
D
laser path
Compact disc tracks spiral out from the centre. The laser passes along a track
at a constant speed, allowing for a longer rotational period towards the outer
edge of the CD.
12
Information systems
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2
The arrows in the diagram below show the direction of energy
transformation in CD use. Write one of these forms of energy as
labels above each energy change below:
•
electrical energy
•
sound energy
•
light energy.
•
kinetic energy
You may use the above forms of energy more than once.
(from power chord)
(from disc spinning around)
(from laser beam)
(reflected light is detected)
(energy conversion in a stereo)
(energy conversion in a computer)
Check your answers.
13
Sound system speakers
Use the stereos section of the audiotape or internet audio files to answer the
following questions on sound system speakers.
The following diagram shows how information from audiotapes and CDs
moves through a stereo. The numbers on the diagram represent an energy
transformation. Write the appropriate transformations of energy in the
spaces provided below the diagram.
audiotape
compact disc
N
wire coil
speaker
wire goes back to
tape and CD player
magnet
S
sound waves
Energy transformations through a sound system speaker.
1
______________________________________________________
2
______________________________________________________
3
______________________________________________________
4
______________________________________________________
5
______________________________________________________
Check your answers.
14
Information systems
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Radios
Use the radios section of the Information systems audiotape/internet audio
files to complete the following activities.
1
2
Label each section of the following diagram of a radio with each of
these labels:
•
speaker
•
demodulator
•
aerial
•
tuner
•
radio frequency amplifier.
Beneath each of the labels, briefly outline the function of each part
of the radio.
radio
Inside a radio.
Check your answers.
Antenna or aerial?
An antenna (plural antennae or antennas) is used to receive information
only. An aerial can transmit, receive or both transmit and receive
information at the same time. Radio and TV stations use an aerial to
broadcast their signals. Radio receivers and TV set receivers receive
signals through aerials that can also be called antennas. A mobile phone
receives and transmits phone calls through an aerial.
Turn to Exercise 1.2 at the back of his part to outline the features various
information systems have in common.
15
Information systems and society
You have been presented with information throughout Part 1 about the
time of development of each information system. The majority of this
information is in the Information transfer section of the Information
systems audiotape or the Part 1 internet audio files.
Each communication system has had an impact on society in a different
way.
16
•
Telephones have allowed long distance communication, allowing the
freedom to move and travel while keeping in touch, reducing postal
demand.
•
Telephones allow people to work from home while keeping in touch
with the company.
•
Advertising, such as telemarketing, can be carried out over the phone
rather than on televisions, in newspapers or on radio.
•
Radios allow people to hear up–to–date news as it occurs.
•
Radios allow a form of advertising for companies and entertainment
for society.
•
Radios have had a huge impact on the music industry, as the latest
music is broadcast worldwide.
•
Television has allowed people to gain clear information on
up–to–date events in the world.
•
Television has provided a form of entertainment any household can
enjoy.
•
Television advertising has proven to be the most effective form of
advertising for many businesses.
•
Fax machines have allowed fast transfer of documents, minimising
the need for postage, thus impacting on the postal system.
•
Fax machines allow information to be transferred at convenient
times, giving people more freedom.
•
Mobile phones allow freedom of movement.
•
Mobile phones allow people in trouble to call for help if within
mobile range.
Information systems
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•
CDs can allow music and information from anywhere in the world to
be stored and transferred to your stereo or computer, allowing you
access to cultures around the world.
•
CDs can be placed in a stacker which a network of computers have
access to; this allows fast access to information without the repetitive
physical loading of a program.
•
Sound systems allow society to appreciate music from around the
world through the use of CDs and tapes.
•
Email allows the convenience of keeping in touch with people from
around the world with print and pictures at a lower cost than via
telephone conversations.
•
Emailing has reduced the need for postal services.
•
Internet chat rooms allow people to interact from around the world
who would not have otherwise interacted; this technology is
expanding the social circles of society.
•
The Internet has allowed society to gain information on any subject
quickly and easily, reducing the need for physical libraries
•
Computer based technologies has allowed the development of
thousands of Internet and computer businesses.
As you can see, communication technologies have had a large impact on
society and will continue to have an impact on society.
In the future, perhaps students will attend school through their computers
from home; university students won’t need to physically attend lectures;
business people won’t need to go to work; people won’t physically go
shopping and so on.
Thirty years ago, there were no computers to access, no Internet to surf
and no CDs. You might wonder what communication technologies your
children will be using in thirty years time.
Turn to Exercise 1.3 at the back of this part to create a timeline of
communication systems development and their impact on society.
17
Advantages of information systems
There are many advantages of having various information transfer
systems available such as mobile phones, fax machines, email, Internet
access, sound systems, radio and television.
18
•
Information may be transferred at the speed of light from one part of
the globe to another via satellites for transmission to televisions,
radios, computers, telephones and fax machines.
•
If one form of information transfer is not successful, other forms
may be used.
•
Computer based information may be sent via the Internet and
received immediately or stored on disc or CD for physical transfer.
•
Forms may be received, filled out and returned through faxes from
anywhere in the world.
•
News from around the world can reach a wide audience through
television or radio transmissions.
•
Sound systems can be used to warn people of potential disasters such
as flood or fire.
•
Business conversations can be held over mobile phones in transit
rather than at particular sites, allowing for greater mobility.
•
CDs can store computer instructions and sound information for
world wide distribution.
•
Recent developments in video conferencing allows people from
around the world to engage in meetings without travelling, thus
saving time and money.
Information systems
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Use the clues below to identify the main advantages of various information
systems.
1
2
3
read
sp
of
4
5
st v
of
Check your answers.
Turn to Exercise 1.4 at the back of this part to discuss the advantages of
using a range of information systems.
19
Summary
Write your own summaries next to each of the following information
systems.
Information system
20
Summary
Information systems
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1
Each of the above information systems all have a basic pattern of
information transfer. Outline the four steps involved in the successful
transfer of information.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
Record the energy transformations involved in the transfer of
information in the following technologies.
television
_____________________________________________________
_____________________________________________________
telephone
_____________________________________________________
_____________________________________________________
mobile phone
_____________________________________________________
_____________________________________________________
21
3
Morse code, using dots and dashes to represent letters, was the
basis of an important information system for about 100 years
until recently. Morse code could be sent through wires using
electricity or wireless (radio) using electromagnetic waves.
Non–electronic
Electronic
Long distance
Short distance
Non–verbal
Code
Verbal
Summarise the features of morse code by placing ticks in this table.
The definitions for the column headings are in the glossary.
Morse code
Check your answers.
22
Information systems
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Appendix
23
24
Information systems
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Suggested answers
Sending messages
1
You have a code for decoding a message.
2
The four things required for the successful transfer of messages are:
a code common to the sender and receiver; a message being sent;
transmission of the coded message; and decoding of the message at
the receiving end.
3
Information transfer systems used on a daily basis for message
transfer are: speech; mobile phones; telephones; fax machines;
computer emailing; Internet; television; radio; CD players; and
pagers. Other answers are acceptable.
Energy
1
Form of energy
Type of energy
chemical
energy stored in chemicals
potential
energy that can be released later
kinetic
movement energy
heat
energy from differences in temperature
light
energy from light source
sound
energy released as traveling vibrations
electromagnetic
energy carried as waves at the speed of light
electrical
energy carried by moving electrons
solar
energy from the sun
nuclear
energy released from converting mass into
energy during fission or fusion
25
2
Scenario
Energy transformation
sound system playing music
electrical
sound
car using fuel
chemical
kinetic
electric light is on
electrical
light (and/or heat)
battery use in a walkman
chemical
sound
boiling an electric kettle
electrical
heat
plants using the Sun’s light
solar
chemical
heating food in microwave
electromagnetic
heat
microwave using electricity
electrical
electromagnetic or heat
storing the Sun’s energy in
batteries
solar
chemical
speaker transforms
electrical impulses
into sound energy
electrical impulses
are sent to
telephone lines
microphone transforms
sound energy into
electrical energy
electrical impulses
entering telephone
electrical impulses
converted into light
energy or
electromagnetic
energy for long
distance transmission
Mobile phones
26
1
Chemical energy is converted to electrical energy using mobile
phone batteries.
2
Sound energy from a voice is converted to kinetic energy of a
microphone diaphragm. The electrical impulses resulting are
converted to electromagnetic energy (microwaves) inside a mobile
phone for transmission to a cell tower.
3
A cell tower boosts a radio wave signal using electrical energy.
4
A message may be sent to the receiving mobile phone as
microwaves from the cell tower or converted to light or electrical
energy for transmission along land connected telephone lines to
another cell tower.
5
The digital mobile network can carry more conversations, more
securely, than an analog mobile network.
Information systems
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Television
1
a) At the transmitting tower, the television signal is converted to
radio waves (electromagnetic energy) and broadcast.
b) A receiving antenna converts the radio waves to electrical
impulses, sending them to the television.
c) The picture tube converts the electrical impulses to a beam of
electrons (kinetic energy) which it fires to the television screen.
d) A television screen is coated in blue, green and red phosphor
that glows when struck by a beam of electrons.
2
A single beam of electrons moves in lines across the screen 60 times
in one second. This causes the phosphor at different parts of the
screen to glow different colours in that time. This glowing creates
an image on the screen.
3
Instead of the electrical impulse being changed to a beam of
electrons directed at a screen, the electrical impulses are used to
create electric fields, which affect the liquid crystals in each pixel.
This causes different parts of the screen to glow particular colours,
forming an image.
1
label
pits that make the
bumps on the other side
acrylic
aluminium
1.2 mm
125 nm
polycarbonate plastic
pits are pressed into the
polycarbonate disc
representing a digital
signal in circular tracks
laser light
directed
this way
electrical energy
2
(from power chord)
kinetic energy
light energy
(from disc spinning around)
(from laser beam)
electrical energy
(reflected light is detected)
sound energy
light energy
(energy conversion in a stereo)
(energy conversion in a computer)
27
Sound system speakers
1
Information is magnetically detected on an audiotape and used to
produce electromagnetic impulses.
2
The electromagnetic information is sent as impulses through wires to
speakers.
3
These electrical impulses moving through a wire coil produce a
changing magnetic field.
4
The magnet vibrates inside the coil as a result of the changing
magnetic field of the wire coil.
5
The movement of the cone attached to the magnet bumps air
particles, causing sound waves.
Radios
radio
aerial
detects all
radio waves
tuner tunes
into a
particular
frequency
radio
frequency
amplifier
boosts the
radio signal
demodulator
carrier wave
removed from
radio signal
speaker
changes the
electrical
signal to
sound energy
Advantages of information systems
28
1
Saves time.
2
Saves money.
3
Speed of information transfer.
4
Worldwide information transfer.
5
Variety of information access.
Information systems
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Summary
1
The four steps for the successful transfer of information are: a code
the sender and receiver both have; a message being sent;
transmission of the coded message; and decoding of the message at
the receiving end.
2
Television: electromagnetic energy (radio waves); electrical energy;
kinetic energy (beam of electrons); light energy.
Telephone: sound energy; electrical energy; (possibly light energy
and back to electrical energy); sound energy.
Mobile phone: sound energy; kinetic energy, electrical energy;
electromagnetic energy; electrical energy; electromagnetic energy;
electrical energy; kinetic energy, sound energy.
Non–electronic
Electronic
Long distance
Short distance
Non–verbal
Code
Verbal
3
Morse code
29
30
Information systems
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Exercises - Part 1
Exercises 1.1 to 1.4
Name: _________________________________
Exercise 1.1
Place a tick or cross in the following boxes indicating if the information
system is: verbal or non–verbal; used over short or long distances; and
electronic or non–electronic.
Non–electronic
Electronic
Long distance
Short distance
Non–verbal
Information system
Verbal
For each one, think if the message uses words or not, if the message can
be sent over a long distance or not and if it uses electrical energy or not.
mobile phone
telephone
television
Internet
radio
audio CDs
CD–ROMs
31
Exercise 1.2
Various information transfer systems have many similarities eg. two
different information systems can utilise digital information transmission
for information transfer. Explain the similarities between the following
information systems.
1
televisions and radios
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
2
radios and mobile phones
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
3
telephones and mobile phones
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
32
Information systems
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Exercise 1.3
1
Use the Information transfer section of the Information systems
audiotape or the Part 1 internet audio files to create a timeline showing
the introduction of each form of communication technology in the table
below.
2
Record one impact each communication system has had on society
on the column indicated.
Timeline of communication systems
Impact on society
2000
1980
1960
1940
1920
1900
1880
1860
1840
33
Exercise 1.4
‘Today, anyone can have access to Internet, email, mobile phones,
telephones, fax machines, radio, television and even video conferencing.
A person running their own lawn mowing business and a stockbroker,
buying and selling shares on the stock market, can both benefit from such
a range of information systems.’
Discuss how the two people mentioned in the above statement could
benefit from the wide range of information transfer systems available.
Record these advantages of information transfer systems in point form in
the table below.
Lawn mowing businessman
34
Stockbroker
Information systems
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Senior Science
HSC Course
Stage 6
Information systems
Part 2: Waves waves waves
2
0
0
I
2
r
be S
o
t
c NT
O
ng DM E
i
t
ra E N
o
rp A M
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nc
Lifestyle chemistry
Information systems
•
Get the message?
•
Waves waves waves
•
More waves
•
Messages from space
•
•
Fibre optics
Option
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Contents
Introduction ............................................................................... 2
What is a wave? ........................................................................ 3
What is the source of a wave? ............................................................4
Waves carry energy .............................................................................5
Sound waves............................................................................. 8
The electromagnetic spectrum ................................................ 10
EMS and communication ...................................................................13
Microwave and radio wave use .........................................................17
Summary................................................................................. 20
Appendix ................................................................................ 23
Exercises–Part 2 ..................................................................... 27
1
Introduction
This part shows how electromagnetic waves can be modulated
(adjusted) to carry information. You will become familiar with parts of
the electromagnetic spectrum and the frequencies that each
communication system uses.
In Part 2 you will be given opportunities to learn to:
•
identify the type of waves in the electromagnetic spectrum
currently used for communication systems as
–
visible light
–
infra–red
–
microwaves
–
radio waves, which include:
–
TV
–
FM radio
–
AM radio
•
compare the advantages and disadvantages of using microwaves
and radio waves in communication technologies
•
identify communication technologies that use energies from the
electromagnetic spectrum for communication purposes
•
describe the individual properties of visible light, radio waves
(AM, FM, TV waves) and microwaves and relate these to their use
in communication systems.
2
Information systems
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What is a wave?
In a communication device, a signal must be carried by something.
If no wires connect two communication devices, the signal must be
carried by a wave.
You are probably familiar with the waves you see at the beach.
The waves in the ocean, that is the ones that aren’t crashing on the
beach, are the shape of the types of waves you will be investigating.
If you were able to look at these waves side–on, you would see they are
in the shape of the wave diagram below. This is just a model of a
wave–not all waves look like the one below.
Standard wave.
•
The highest point of a wave is the crest.
•
The lowest point of a wave is a trough.
•
The distance from crest to crest or trough to trough is one
wavelength.
•
The number of waves to pass a point (like a lighthouse) in one
second is called the wave frequency.
1
On the above diagram, label the following:
a) crest
b) trough
c) wavelength
3
2
Frequency is the number of wavelengths to pass a point in one
second. The units of frequency are hertz (Hz).
a) If 10 waves pass a point in one second, what is the in
frequency?
__________________________________________________
b) If 25 waves pass a point in one second, what is the in
frequency?
__________________________________________________
c) If 300 waves pass a point in one second, what is their
frequency?
__________________________________________________
Check your answers.
You are not required to calculate wave frequencies in this course,
however this activity will help you understand wave classification
based on wave frequencies later in this part.
What is the source of a wave?
So what actually produces a wave? Do you have any ideas?
You probably know that when you throw something into a still body of
water, like a lake or puddle, that waves are produced. This is due to the
initial disturbance of the water particles, or the initial vibration.
Imagine you have set up the apparatus in the following diagram.
A mass is attached to a hanging spring and a pen is attached to the
mass. If you pulled on the mass then let it go, the mass would bob up
and down. The pen will mark out a vertical straight line on the paper as
the mass is in motion.
vibration
direction
straight line
paper is stationary
Mass
on the end of a spring in motion.
4
Information systems
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Now imagine the paper is moving at a constant speed past the pen as the
mass is bobbing up and down at a constant rate. The pen will mark out
the following wave.
vibration
direction
trace left by pencil is a sine wave shape
paper moving at constant speed
Mass on the end of a spring in motion. A pencil attached to the mass is
marking out a wave as the paper moves past the pencil at a constant rate.
You should notice that:
•
the mass is the vibrating object
•
the mass moves up and down (not forward and back)
•
the wave produced is at right angles to the motion of the mass
•
the vibration causes a wave form.
Waves are caused by a vibrating object or particle.
Waves carry energy
If you have ever been dumped by a wave at the beach, you would have
felt the energy of the wave. Even small waves carry energy from one
place to another.
Different types of waves carry different types of energy and therefore
different types of information. For this reason, waves are classified
according to their properties.
There are two main groups of waves. They are electromagnetic waves
and mechanical waves. The characteristics of each type of wave are
outlined in the chart on the following page.
5
Waves
electromagnetic
mechanical
do not require medium
for transmission
do require medium
for transmission
all transverse
alternating
electric and
magnetic fields
operating
perpendicularly
to the direction
of wave travel
transverse
particles vibrate
perpendicularly
to the direction
of the wave
propagation
longitudinal
particles vibrate
in the same
direction as
wave
propagation
Different wave types can be classified according to the energy they comprise
or the source of the vibration (or disturbance) producing the wave.
1
Which waves do not require a medium (such as a solid, liquid or gas)
for transmission?
_____________________________________________________
2
Which types of wave transfers energy perpendicular to an electric field
or particle movement?
_____________________________________________________
3
Which wave type is produced by particles vibrating in the same
direction as the flow of energy?
_____________________________________________________
4
Which wave type requires a medium (such as a solid, liquid or gas) for
wave transmission?
_____________________________________________________
6
Information systems
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A vacuum is a space that contains no particles of matter. This means it
is entirely empty of solids, liquids and gas. Outer space is a natural
example of a vacuum as it contains no matter.
5
Can electromagnetic waves travel through a vacuum? Explain
why or why not.
_____________________________________________________
_____________________________________________________
6
Can mechanical waves travel through a vacuum? Explain why or
why not.
_____________________________________________________
_____________________________________________________
Check your answers.
Mechanical waves can only deliver information over short distances
due to the nature of the waves. Sound waves are an example of
mechanical waves, which will be addressed later.
Many communication systems use electromagnetic waves for
information delivery. These can transfer information quickly and over
enormous distances.
Turn to Exercise 2.1 at the back of this part to practice classifying waves.
7
Sound waves
Turn to the classification of waves chart on page 6. You are about to
perform an investigation of mechanical longitudinal waves (these on
the right of the chart).
Sound waves are mechanical longitudinal waves. What this means is
that air particles must bump into each other in order for sound to travel.
Sounds in air travel like the compressions in this slinky spring.
compression
rarefaction
rarefaction
compression
The springs compress and rarefact as the wave pulse moves along the spring.
The areas where the spring is compressed is called a compression.
Where the spring has greater space between the springs, it is called a
rarefaction.
In transverse waves, the wavelength is usually measured from crest to
crest. Longitudinal wavelengths are measured from compression to
compression or rarefaction to rarefaction.
8
Information systems
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The air particles below show what longitudinal waves look like in air
close up. Notice the compressions and rarefactions in the sound wave.
wavelength
Air particles compress together as sound waves move through air.
Air particles move in the same direction as the sound energy.
Without air particles, sound energy has no medium to be transferred to,
therefore sound energy cannot travel.
9
The electromagnetic spectrum
Do you know what the electromagnetic spectrum is?
The electromagnetic spectrum (EMS) is responsible for sun burn,
X–rays, everything you see, the heating of food, the music you hear on
the radio, the shows you watch on television and much more.
So what is the electromagnetic spectrum?
The electromagnetic spectrum is a continuum of electromagnetic
waves, which are arranged in order of frequency and wavelength.
If that sounds too technical, the following diagram should help as it
demonstrates the various electromagnetic waves of the electromagnetic
spectrum.
gamma
rays
x-rays ultraviolet
infra-red
light
radio waves
radio
microwaves TV
electrical
power
1 cm
103 km
Wavelength
0.01 nm
1 nm
0.1 mm
0.01 mm
1m
1 km
0.4–0.7mm
The electromagnetic spectrum is arranged in order of increasing wavelength.
Adapted from OTEN, Physics for Electrical and Electronic Engineers.
Did you notice the units ‘nm’, and ‘mm’?
These units indicate nanometres (10–9 m) and micrometres (10–6 m).
It may be useful to think of the different wavelengths in the
electromagnetic spectrum in the following ways.
10
Information systems
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Use the diagram on the previous page to answer the following questions.
1
Highlight or underline which of the following has the shorter
wavelength.
a) Gamma rays or television radio waves.
b) Infra–red waves or X–rays.
c) Ultraviolet waves or visible light.
d) Microwaves or infra–red waves.
All electromagnetic waves travel at the same speed which is the speed
of light. If a wave has a small wavelength, more waves are able to pass
a point in one second than a longer wavelength. Keep this in mind as
you answer the following questions.
2
Highlight which of the following are likely to have a higher
frequency? (This means the waves are smaller and therefore more
waves are likely to pass a point in one second.)
a) Microwaves or television radio waves.
b) Infra–red waves or gamma rays.
c) Ultraviolet waves or infra–red waves.
d) X–rays or visible light.
Check your answers.
Remember–electromagnetic waves do not need a medium to be
transmitted through, however, particular solids, liquids and gases can
absorb particular electromagnetic wavelengths, stopping their
transmission.
The following page displays diagrammatic information on the relative sizes
of different wave types and instructions for eight activities.
You will need coloured pencils to carry out the eight activities indicated in
the diagram.
11
Information systems
ctr o
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waves can fit into a
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with viewing these waves in
thermography from the Medical
Technology-Bionics module. If you
have seen the movies Hollow Man
or Predator, you have seen
evidence of infrared waves.
Your body is even emitting
infrared radiation as you
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12
By now you probably have a good idea that different wavelengths and
frequencies in the electromagnetic spectrum are used for different
communication systems.
lo
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Gamma rays
with 0.01 nm
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they can affect the genes
inside cells. This is why
gamma rays are so
dangerous.
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Gill Sans Bold
EMS and communication
Visible light and infra–red waves
Remember–if one wave passed a point in one second, it would have a
frequency of one hertz. If one thousand waves pass a point in one
second, it would have a frequency of one kilohertz (kHz).
Visible light has a wavelength of 700 to 400 nm.
Infra–red waves have a wavelength of 700 nm to 1 mm.
Visible electromagnetic waves are the colours of the rainbow.
Together, all the colours make up white light. Visible light is used to
scan pages in fax machines. Visible light waves and infra–red light
waves are used to transmit digital information at the speed of light
through optical fibre telephone lines. (Optical fibres will be further
discussed in Part 6 of this module.)
Fax machines, telephones and computer based communication
systems all rely on information transmission through telephone lines.
These communication systems use the visible light and infra–red
sections of the electromagnetic spectrum for communication through
optic fibres.
Bar codes are scanned using visible light. You may have noticed the
red light that is projected onto purchase items at the checkout. This is
visible light used to scan the bar code.
Microwaves
Microwaves are a type of radio wave with a wavelength from 1 mm to
30 cm wavelengths. The type of radio waves mobile phones utilise for
information transmission are microwaves at 824 to 849 megahertz
(MHz). This means 824 to 849 million cycles per second or 824 000 to
849 000 kHz. Land–based telephone systems also use microwave
towers to transmit information over long distances to the next
microwave tower, rather than lay hundreds of kilometres of cables.
Microwaves are used in satellite communication using various
frequencies.
13
Radio waves
Radio waves have wavelengths ranging between 30 cm and 1 km.
The following information outlines the uses of various wavelengths in
communication.
AM radio waves
AM radio waves are transmitted at 335 kHz to 1.7 MHz (1700 kHz).
These waves carry information on amplitude modulated (AM) waves.
A standard carrier wave, using the frequency allocated to the AM radio
station, is combined with the speech wave from the radio announcer or
music wave from the radio station. The amplitude of the carrier wave is
modified by the speech or music wave from the radio station.
The carrier wave is removed from the radio wave inside a radio receiver
to select only the speech or music frequencies from the radio station.
AM modulated carrier
Notice the amplitude or the height of the wave is modified (modulated)
in the above diagram.
Two–way radios use AM radio waves in much the same way.
FM radio waves
FM radio transmissions occur at frequencies of 88 up to 108 MHz
(88 000 kHz to 108 000 kHz). The waves carry information on a
frequency modulated (FM) wave.
A carrier wave’s frequency is altered with the addition of speech or
music from the radio station. Instead of modifying the amplitude or
size of the carrier wave, it alters the frequency of the wave
transmission. This means the number of waves to pass a point in one
second varies as shown by the following diagram.
14
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FM modulated carrier
Notice the number of wavelengths to pass a point varies according to
the signal.
FM radio stations use FM radio waves for communication.
Television
Television broadcasting stations transmit their television programs
using at least two FM signals. One signal carries the information for
the television picture and the other carries sound information.
Colour broadcasting uses one FM signal for each phosphor colour on a
television screen, plus an FM sound signal. Sound accompanying a
television broadcast, is transmitted at 5 MHz above the frequency of the
television signal.
Television channels numbers 2–6 transmit at the radio wave frequencies
of 54 MHz (54 000 kHz) to 88 MHz (88 000 kHz) using an FM signal.
Aerial length
Aerial length is about the same order of magnitude as the wavelength
of the electromagnetic waves it is designed to transmit or receive.
The aerial in a mobile phone that receives and transmits microwaves is
only centimetres in length. The metal wire or metal parts in an
aerial/antenna for an FM radio receiver or TV set are closer to a metre
in length. AM radio receivers have many turns of metal wire that can
be hundreds of metres in length in their aerial/antenna. Similarly
transmitting aerials for AM radio are much longer than for FM stations.
Frequency
The table on the following page shows the parts of the electromagnetic
spectrum which are used for communication purposes.
1
Record the frequencies in the frequency column on the electromagnetic
chart on the following page for each communication system from the
text on pages 13–15.
*
2
Cut out the pictures in the Appendix and glue them in the
Communication systems column in the chart on the following page.
15
Wave frequency
Wave type
Frequency
Communication system
using wave
visible light
infra-red
microwave
FM radio waves
TV radio waves
AM radio waves
Check your answers.
Turn to Exercise 2.2 at the back of this part to identify the types of waves in
the electromagnetic spectrum used in communication.
16
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Microwave and radio wave use
Microwaves are a part of the spectrum of radio waves. When people
refer to radio waves, they are generally referring to the usual AM and
FM radio waves used in radio station and television station
transmissions. Microwaves have a smaller wavelength and a higher
frequency than the general radio waves. It is these properties that make
microwaves more or less useful than general radio waves.
Microwaves
There is little difference between frequency modulated (FM) radio
waves and the frequency modulated microwaves used to send signals
from mobile phones. The only difference is the frequency bandwidth.
Microwave towers can be seen in many parts of inland Australia, on
hills and high buildings in country towns. These microwave
transmission towers have replaced the need to connect distant parts of
Australia by landlines.
The benefits of microwave use in communication are as follows:
•
Microwaves are on a different bandwidth of frequency to radio
waves on the electromagnetic spectrum. Crowding of the radio
wave bandwidths is a problem.
•
Microwaves do not spread out very much so most of the energy
makes it to the next receiver dish from the transmitter. This results
in a signal with the potential range of up to 100 km. Such a system
is important to send information over long distances from tower to
tower on telephone networks, removing the need for cables.
•
It is possible to send a large number of signals at once, because the
range of frequencies in the microwave transmission range is large.
•
Because microwaves have a shorter wavelength, microwaves have
a higher frequency. This means that more information can be
transmitted through microwaves in the same amount of time than
radio waves, which have a lower frequency.
•
Microwaves can also be received and retransmitted by satellites,
expanding the receiving and transmitting area for microwave
communication.
•
Higher frequency waves such as microwaves need less electrical
power for transmission than lower frequency waves such as radio
waves.
17
Disadvantages of microwave use in communication are as follows:
•
Microwaves travel in straight lines and therefore require a line of
sight connection from one antenna to the next. Because of this, a
mobile network needs a huge number of antennae. Transmitting
and receiving aerials used in remote areas for telephone
transmissions without cables need to be built up to 90 m tall for
line of sight access to towers 50 to 80 km away.
•
Because microwaves travel in straight lines, microwave signals
may be blocked by hills and mountains. This could be the reason
for mobile phone connections dropping out whilst in transit.
•
Microwaves heat food by water molecules within the food
absorbing the waves. This fact explains microwave transmission
difficulties during rain and high humidity as water molecules in the
air tend to absorb the microwaves.
•
Microwave transmission over the ocean is less successful than
transmission over land as water tends to absorb some of the energy.
•
Cell antennas are usually mounted very high on cell towers to have
line of site access over a ten kilometre square area. Interruptions to
line of site transmission by hills and buildings can disrupt
microwave–based conversations.
•
Microwave signals must be relatively strong for information
transfer to occur. The microwave signal is strongest at the cell
tower, losing its strength as it radiates in all directions from the
tower. Towards the outskirts of a cell area, mobile phone
connections tend to break up in clarity or drop out of range. This is
because the microwave signal is not strong enough to be
transformed into electrical impulses by the mobile phone aerial.
Radio waves
Radio waves are beneficial in communication systems for the following
reasons:
18
•
Some radio waves can be transmitted into space and reflected off
satellites. Radio waves are therefore useful for reaching long
distances.
•
AM radio waves, unlike FM radio waves and microwaves, do not
require line of sight access for successful transmission. AM radio
waves can be reflected off objects such as hills, the Earth’s surface
and layers of the atmosphere. This allows AM radio wave
transmission to distant and remote places without the use of
satellites.
•
AM radio waves of high frequency called short waves (SW) can
travel further at night. Atmospheric layers alter their altitude with
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night–fall, allowing radio waves to be reflected over longer
distances. This is often the reason why at night you can tune into
radio channels broadcast from overseas that cannot be detected
during the day.
The disadvantages of radio wave use in communication technologies
are as follows:
•
Radio waves can be absorbed by water, oxygen and carbon dioxide
in the atmosphere, reducing signal intensity.
•
Radio waves can be affected by static produced by passing cars,
overhead power lines and lightning.
•
Low frequency waves such as radio waves need more electrical
power for transmission than higher frequency waves such as
microwaves.
•
Heavy rainfall can absorb radio waves, affecting their transmission.
•
Radio wave transmission over the ocean is less successful than
transmission over land as water tends to absorb some of the energy.
•
AM radio waves are more affected by atmospheric conditions and
frequency ‘noise’ than FM radio waves and microwaves. This
results in static upon reception.
•
Because radio waves can be reflected off objects such as land and
atmospheric layers, the same signal can arrive at a receiver at
slightly different times. This can leave a ghosting effect on
televisions and an echo sound on radios.
Turn to Exercise 2.3 at the back of this part to compare the use of radio
waves and microwaves in communication.
19
Summary
1
Write three multiple choice questions and their answers based on the
information in this part. Make the questions as challenging as you
would expect in an exam.
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2
Write two short answer questions and their answers based on the
information in this part. Room for questions is also available on
the following page.
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3
Write one long answer question with its answer based on the
information in this part.
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_____________________________________________________
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_____________________________________________________
21
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22
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formulas
equations
calculations
particles
energy
interactions
H2O
O H O
H H H
MICRO
O
H H
observe
infer
understand
SYMBOLIC
O H
H
MACRO
Appendix
AM
radio
optic fibre
FM
radio
23
24
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Suggested answers
What is a wave?
wavelength
1
crest
trough
2
a) The wave frequency is 10 Hz.
b) The wave frequency is 25 Hz.
c) The wave frequency is 300 Hz.
Waves carry energy
1
Electromagnetic waves do not require a medium for transmission.
2
Transverse waves transfer energy perpendicular to an electric field
or particle movement.
3
Longitudinal waves vibrate particles in the same direction as the
flow of energy.
4
Mechanical waves require a medium for wave transmission.
5
Electromagnetic waves can travel through a vacuum because they
do not require a medium for transmission.
6
Mechanical waves cannot travel through a vacuum because they
require a medium for transmission.
25
The electromagnetic spectrum
1
a) Gamma rays have a shorter wavelength than television radio
waves.
b) X–rays have a shorter wavelength than infra–red waves.
c) Ultraviolet waves have a shorter wavelength than visible light.
d) Infra–red waves have a shorter wavelength than microwaves.
2
a) Microwaves have a higher frequency than television radio
waves.
b) Gamma rays have a higher frequency than infra–red waves.
c) Ultraviolet waves have a higher frequency than infra–red
waves.
d) X–rays have a higher frequency than visible light.
Electromagnetic waves and communication
Wave frequency
Wave type
visible light
Frequency
Communication system
using wave
8 million
megahertz
optic fibre
26
infra-red
4 million
megahertz
microwave
824–849
megahertz
FM radio waves
88–108
megahertz
FM
radio
TV radio waves
54–88
megahertz
television
AM radio waves
535 kilohertz–
1.7 megahertz
AM
radio
mobile
phone
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Exercises - Part 2
Name: _________________________________
Exercise 2.1
Identify the following waves as one of the following wave types:
•
electromagnetic transverse wave
•
mechanical transverse wave
•
mechanical longitudinal wave.
You may need to refer to page 6 to help you with your answer.
Wave
Wave classification
microwave travelling through space
wave travelling in the ocean
sound travelling through air
27
Exercise 2.2
1
2
28
Use the scale on the following page to mark the frequency of the
electromagnetic spectrum of following wave types:
•
microwaves
•
infra–red
•
visible light
•
radio waves used to broadcast
•
TV
•
AM
•
FM .
Next to each wave type, record which of the following
communication systems uses one of the listed frequency ranges
during communication:
•
optic fibre infra red information transfer
•
television
•
AM radio
•
mobile phone
•
optic fibre visible light information transfer
•
FM radio.
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Frequency
Wave type
Communication
technology using this
wave frequency
8 000 000 000
kHz
___________________
_____________________
4 000 000 000
kHz
___________________
_____________________
___________________
_____________________
___________________
_____________________
___________________
_____________________
___________________
_____________________
849 000 kHz
824 000 kHz
108 000 kHz
88 000 kHz
54 000 kHz
1 700 kHz
535 kHz
29
Exercise 2.3
Advantages
Disadvantages
radio waves
microwaves
Wave
Many of the advantages and disadvantages of using radio waves and
microwaves are identical. Use the information on microwaves and
radio waves for communication to identify the benefits and
disadvantages of microwave and radio wave use in communication
systems.
30
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Senior Science
HSC Course
Stage 6
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Part 3: More waves
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Lifestyle chemistry
Information systems
•
Get the message
•
Waves waves waves
•
More waves
•
Messages from space
•
•
Fibre optics
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Contents
Introduction ............................................................................... 2
Properties of the EMS ............................................................... 3
Speed of travel .....................................................................................3
Ability to travel in a straight line ...........................................................4
Ability to be reflected............................................................................5
Wave modulation....................................................................... 7
AM and FM radio waves ......................................................................8
Summary................................................................................. 11
Exercises–Part 3 ..................................................................... 17
Part 3: More waves
1
Introduction
Part 3 looks in closer detail at the properties of electromagnetic waves
and their uses in information systems. You will perform an investigation
to observe communication with AM and FM waves.
In this part you will be given opportunities to learn to:
•
identify that where information systems cannot be physically linked
the information may be transmitted in wave form through the
atmosphere or space
•
identify the properties of energy from the electromagnetic spectrum
that make it useful in communication technologies including its
–
speed of travel
–
ability to travel in a straight line
–
ability to be reflected
In this part you will be given the opportunities to:
•
perform a first–hand investigation to observe ways in which waves
can be modified to carry different types of information
•
plan, choose equipment or resources for, and perform a first–hand
investigation to compare the quality of reception of AM and FM
radio waves.
2
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Properties of the EMS
Three useful properties of energy from the electromagnetic spectrum are:
•
the speed of travel
•
ability of waves to travel in a straight line
•
ability of waves to be reflected.
Speed of travel
All waves in the electromagnetic spectrum travel at the same speed–the
speed of light. Light travels at 300 000 km per second. All
electromagnetic waves travel at this speed.
It might be difficult to comprehend just how quickly these waves travel.
An electromagnetic wave can travel around the Earth more than six times
in one second. That’s pretty fast!
Use a pencil to draw a cartoon demonstrating electromagnetic waves
travelling at high speed. Be as inventive as you like!
Part 3: More waves
3
You outlined the communication technologies which use part of the
electromagnetic spectrum for communication purposes in Part 2.
Outline why the speed at which waves travel is important in communication
technologies such as in telecommunications.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Ability to travel in a straight line
Electromagnetic waves travel in straight lines unless acted on by a
influencing field. This is an important aspect of electromagnetic waves
as they can be directed to a specific receiving dish, allowing line of
sight transmissions in communications eg. microwave transmissions
from telecommunications towers.
This property of electromagnetic waves also allows waves detected from
space to be used to pinpoint the location of the transmitting signal.
This allows scientists to locate and map stars and galaxies, control
astronomical instruments on satellites and track the passage of spacecraft
through space.
Draw a cartoon demonstrating electromagnetic waves travelling in straight
lines.
4
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Explain why electromagnetic waves travelling in straight lines is an
important property for use in communication technologies.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Ability to be reflected
Electromagnetic waves can be reflected off surfaces. This is a very
important property of electromagnetic waves. Reflection allows:
•
waves to be transmitted across the globe using the reflective
properties of the ionosphere and the Earth’s surface
•
a weak signal to be collected by a receiving dish.
The diagram below shows a transmitting tower sending electromagnetic
waves. The wave travels through the atmosphere in a straight line and is
reflected by the ionosphere. From here, the wave bounces back to Earth
where it can then be reflected off the surface of the Earth and so on.
1
Label the following on the diagram below based on the information
from the previous paragraph:
•
transmitter
•
reflected wave
•
ionosphere
Earth
An electromagnetic wave is reflected off the ionosphere, allowing the wave to be
transmitted to parts of the globe with no line of sight.
Part 3: More waves
5
Waves can be collected and reflected to a single point by a satellite dish.
The following diagram demonstrates how the curvature of the dish
allows the focusing of the reflected waves to the receiver.
Pay TV delivered without cables relies on information transfer in this
way. Telecommunications towers also rely on the principles of wave
reflection at the satellite dish. Communication with space shuttles and
receiving information from space probes in outer space relies on the
same principles–on a much larger scale.
2
Label the satellite dish and the reflected waves on the following
diagram.
A satellite receiving dish utilising the reflective properties of waves to focus the
waves to a receiver.
3
Explain the importance of the reflective capabilities of
electromagnetic waves in their use in communication technologies
such as receiving dishes.
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Although the speed of electromagnetic waves, their ability to travel in
straight lines and their reflective capabilities remain constant, waves can
be modified to carry different types of information.
Turn to Exercise 3.1 at the back of this Part to outline the properties of
waves from the electromagnetic spectrum that make those electromagnetic
waves useful in communication technologies.
6
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Wave modulation
You might not realise that a change in the pitch of a sound or a change in
sound volume is a result of wave modulation. The different colours you
see are a result of wave modulation. Particular colour wavelengths are
removed when white light reflects from objects resulting in you seeing a
particular colour. Infra–red waves are modified by differences in heat.
Radio waves are amplitude modulated for AM radio, or frequency
modulated for FM radio.
In each instance, wave modulation (modification) allows different
information to be transmitted.
A wave can be modulated in two main ways:
•
amplitude modulation (the height of the waves)
•
frequency modulation (the number of waves which pass a point in
one second)
Imagine modulating the simple wave below.
1
Redraw the above wave with its amplitude (the height of the wave)
modulated.
Part 3: More waves
7
2
Redraw the original wave with a modulated frequency (the number
of waves to pass a point).
Turn to Exercise 3.2 at the back of this part to modulate waves to carry
different information.
AM and FM radio waves
AM and FM radio waves are the result of modulated carrier waves.
AM waves are an amplitude modulated carrier wave and FM waves are a
frequency modulated carrier wave.
Part 2 discussed the differences between AM radio waves and FM radio
waves. You may need to use this information to answer the following
question.
8
1
Draw an AM wave below.
2
Draw an FM wave below.
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3
Outline the main difference between AM and FM radio waves.
_____________________________________________________
_____________________________________________________
_____________________________________________________
The atmosphere often contains ‘noise’ that can interfere with an
electromagnetic wave such as a radio wave. Have you ever noticed a
radio signal sound scratchy as you drive under power lines or your
television picture becoming fuzzy when an electrical appliance in the
house is running? This is because an electromagnetic field is interfering
with the radio wave, which in turn, causes the signal to become fuzzy.
AM radio waves are easily affected by ‘noise’. The following diagram
demonstrates how this noise combines with an AM wave, causing a
fuzzy reception.
amplitude modulated signal
plus noise signal
equals modified AM signal – this is alteration that produces
the static you hear
AM signal plus noise.
FM radio waves rely on altering the frequencies of the wave rather than
the wave amplitude. It is much harder to change the frequency of a wave
through noise, therefore FM reception is much clearer than AM
reception.
Part 3: More waves
9
4
Which type of radio waves are more likely to be affected by static?
Briefly explain your choice.
______________________________________________________
______________________________________________________
______________________________________________________
FM radio channels require a large bandwidth of the electromagnetic
spectrum. The range of frequencies required to transmit the signal is
large. This limits the number of FM channels available.
AM radio requires a much smaller bandwidth of frequency for
transmission so the number of potential AM channels transmitted is
much larger.
Again, you may need to use the information on AM and FM waves in
Part 2 to answer the following questions.
5
What frequency bands do AM radio stations use?
______________________________________________________
6
What frequency bands do FM radio stations use?
______________________________________________________
7
Which radio signal uses higher frequencies, AM or FM?
______________________________________________________
Check your answers.
Waves from the electromagnetic spectrum are used in ways you may not
have thought of.
Turn to Exercise 3.3 at the back of this part to plan and carry out an
investigation comparing AM and FM radio communication.
10
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Summary
1
Satellite dishes rely on which property of electromagnetic waves to
focus the waves onto a receiver?
_____________________________________________________
2
You can have a conversation on a mobile phone with someone 5000 km
away with no time delay in the conversation due to which property of
electromagnetic waves?
_____________________________________________________
Circle the correct answer for questions 3–4.
3
Changing the pitch of a sound is the result of changing the wave:
frequency; amplitude; plane of vibration.
4
Changing the volume of a sound is the result of changing the wave’s:
frequency; amplitude; plane of vibration.
5
What are the two main ways of modulating radio waves?
_____________________________________________________
6
Explain the difference between AM and FM radio waves.
_____________________________________________________
_____________________________________________________
7
Explain why AM waves are more affected by static than FM waves.
_____________________________________________________
_____________________________________________________
Part 3: More waves
11
12
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Suggested answers
Speed of travel
Telecommunications benefit from the speed of information transfer as
phone calls and satellite communications from across the globe, such as
the transmission of live television programs from other countries, are
achieved at a fast rate without time delay.
Ability to travel in a straight line
Electromagnetic waves can be focused to a point for collection at a
distance due to the fact that the waves travel in straight lines.
The location of stars, galaxies and space shuttles can also be pin pointed
due to this property of electromagnetic waves.
Ability to be reflected
ionosphere (atmosphere layer)
1
reflected wave
transmitter
Earth
2
reflected waves
satellite dish
Part 3: More waves
13
3
The reflective capabilities of electromagnetic waves allows waves to
be reflected to a receiver. This is important in communication from
space, pay TV using satellite dish technology and
telecommunications. Electromagnetic waves being reflected off
atmospheric layers allows transmission further around the globe
without the use of repeater stations eg. radio wave transmissions.
Wave modulation
1
2
AM and FM radio waves
1
2
14
3
The amplitude of a carrier wave is modified to carry an AM radio
signal. The frequency of the carrier wave is modified to carry an FM
signal.
4
AM radio waves are more likely to be affected by static than FM
waves because the amplitude of a radio wave is more easily affected
by ‘noise’ than the frequency of a wave.
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5
AM radio stations use frequency bands from 335 kHz to 1.7 MHz.
6
FM radio stations use frequency bands from 88 to 108 MHz.
7
FM radio uses higher frequencies than AM radio.
Summary
1
Satellite dishes rely on the reflective properties of electromagnetic
waves to focus the waves to a receiver.
2
You can have a conversation on a mobile phone with someone
5000 km away with no time delay due to the speed of
electromagnetic waves.
3
Changing the pitch or tone of a sound is the result of changing the
wave frequency.
4
Changing the volume of a sound is the result of changing the wave’s
amplitude.
5
Amplitude modulation (AM) and frequency modulation (FM).
6
AM radio waves carry information in a carrier wave with a modified
amplitude. FM radio waves carry information on a carrier wave with
a modified frequency.
7
AM waves are more affected by static than FM waves because wave
amplitude is more easily affected by ‘noise’ than wave frequency.
Part 3: More waves
15
16
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Exercises - Part 3
Name: _________________________________
Exercise 3.1
Identify three properties of waves from the electromagnetic spectrum
that are useful in communication technologies.
For each, outline the importance of the property in terms of information
transmission where the information systems cannot be physically linked.
i)
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
ii)
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
iii) _____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 3: More waves
17
Exercise 3.2 Observing ways in which waves can be
modulated to carry information
Amplitude
The first way you will modify a wave is by changing the amplitude of a
wave. Believe it or not, when your parents complain about the volume of
your music, they are actually complaining about the amplitude of the
waves coming from the speakers.
If you have a guitar, violin or any other string instrument, you can use it
for the following activity. If not, you can achieve the same outcome with
a tightly pulled rubber band between two fingers or two objects kept the
same distance apart.
1
Gently pluck one string on a musical instrument or a tightly pulled
rubber band. You should hear a sound and see the string or rubber
band vibrating. Notice the volume of the note and the size of the
string or rubber band vibrations.
Record your observations below.
______________________________________________________
______________________________________________________
______________________________________________________
2
Now pluck the string or rubber band harder. What difference is
there in the sound? Look at the vibration of the string–how is it
different to plucking the string or rubber band gently?
Record your observations below.
______________________________________________________
______________________________________________________
______________________________________________________
3
The amplitude of the string or rubber band is altered by how hard
you pluck the string or rubber band. Explain how this relates to the
difference in sound that is heard.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
18
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Frequency
You can alter the frequency of a wave using the same string instrument
or rubber band.
4
If using a string instrument, pluck one string with your finger
holding down the string in one place. Repeat this with your finger in
different places on the string as shown below.
If you are using a rubber band, alter the tension on the rubber band
by loosening it or pulling it tighter then pluck it. Repeat this with a
different tension on the rubber band.
What do you notice about the sound as you pluck the string or rubber
band?
_____________________________________________________
_____________________________________________________
_____________________________________________________
5
Holding the string in different places puts more or less tension on the
string as does altering the tension of the rubber band. Altering the
tension alters how quickly the string is able to vibrate. Use your
observations to fill in the missing words below with the words
higher or lower.
a) The more tension on the string, the _________________ the
frequency and the _________________ the pitch.
b) The less tension on the string, the _________________ the
frequency and the _________________ the pitch.
6
Sound waves clearly carry information. Describe how that
information carried by sound waves changes when
a) the amplitude increases ________________________________
_____________________________________________________
b) the frequency increases ________________________________
_____________________________________________________
Part 3: More waves
19
Exercise 3.3
You must plan, choose equipment and resources for and perform an
investigation to compare the quality of reception using AM and FM
radio waves.
You have access to AM and FM radio waves through your radio receiver.
If you live somewhere where you do not receive AM and FM radio
signals, you may plan your investigation now and complete it when
passing through towns on your next trip using the car radio.
You must carry out the following tasks in your investigation.
•
Record the radio stations you are investigating and their frequency
[remember 900 2LM really stands for 900 kilohertz (kHz) and
96.1 FM really stands for 96.1 megahertz (MHz)].
•
Record the bandwidth you can pick the signal up on with some static
eg. 900 2LM could be received over 895–905 kHz.
•
Record the quality of AM reception compared to FM reception.
•
Draw conclusions as to why a radio signal can be received over a
bandwidth range, linking it to the information on page 10.
•
Draw conclusions on the clarity of signal received on AM and FM
bands and relate these to AM and FM radio wave transmissions.
Here are some suggestions for your investigation.
20
•
Compare the reception of AM and FM radio signals when in an area
of interference such as under power lines.
•
Try several different AM and FM radio stations.
•
Try to chose AM and FM signals that are strong.
•
Predict the results you expect in a column in your results table such
as the bandwidth you expect to receive a particular radio station over
and the clarity of reception.
•
Assess the accuracy of your predictions in your discussion.
•
Comment on anything that went wrong in your discussion such as a
weak signal.
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Record your investigation using the following scaffold.
Aim
What are you investigating?
_________________________________________________________
_________________________________________________________
Method
What steps are involved in carrying out the experiment? Try to address
all the points above.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 3: More waves
21
Results
How will you present your results? Will you make any predictions?
If so, clearly state they are predictions as opposed to results. Make sure
your results are clear and easy to understand.
Discussion
Assess the accuracy of any predictions and give scientific reasons for
your results. Discuss any situational issues such as poor radio reception
and how the experiment could be improved.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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Conclusion
Explain the similarities and differences between AM and FM radio
signals that are supported by your results. Link your results to your
knowledge of AM and FM radio waves from pages 8 to 10.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 3: More waves
23
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Senior Science
HSC Course
Stage 6
Information systems
Part 4: Messages from space
0
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Lifestyle chemistry
Information systems
•
Get the message?
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Waves waves waves
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More waves
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Messages from space
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Fibre optics
Option
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Contents
Introduction ............................................................................... 2
Geostationary satellites ............................................................. 3
Use of geostationary satellites.............................................................5
Earth–based satellite dishes................................................................7
Satellite orbits.......................................................................... 11
Satellites.................................................................................. 14
Summary................................................................................. 15
Appendix ................................................................................. 17
Exercises–Part 4 ..................................................................... 23
1
Introduction
Almost everything you ever wanted to know about satellites is addressed
in this part. You will learn about: satellite orbits; what satellites are used
for; various parts of satellites; and the importance of calibrating satellite
dishes for optimum reception.
This part deals with geostationary satellites and how they relay and
transmit information.
•
explain why the satellite must be at a height where its revolution
period is the same as that of the Earth’s period of rotation
•
explain why the Earth–based satellite dish must face a fixed
direction if it remains in the same location with respect to the
geostationary satellite.
•
gather, process and analyse information from secondary sources to
identify the satellites used for ‘live’ telecasts from other regions of
the world to Australia and vice versa and to present reasons why
communication satellites have different aerials and positional orbits.
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Geostationary satellites
1
Collect a round piece of fruit such as an apple, orange or peach.
2
Stick a toothpick (or a small stick) into the piece of fruit.
3
On the other end of the toothpick (or stick), place a small object such as
a raisin, jelly bean or a ball of Blutac® .
4
Move the round piece of fruit through a 360° rotation. Notice the
position of the small object on the end of the toothpick through the
rotation.
5
Draw your apparatus below using arrows to indicate the rotation of
the fruit, the toothpick and the object on the end of the toothpick.
Keep your model for an experiment later in this part.
You have just demonstrated the action of a geostationary satellite.
You should know that satellites are objects held in orbit around a planet
by the planet’s gravitational pull. But what does geostationary mean?
6
What do you think geo means?
_____________________________________________________
_____________________________________________________
3
7
Explain the term stationary.
______________________________________________________
______________________________________________________
8
What do you think is meant by the term geostationary satellite?
______________________________________________________
______________________________________________________
Check your answers against the following definition.
Geostationary satellites are held in a fixed position in orbit above
the Earth.
Geostationary satellites orbit around 36 000 km above the Earth’s
surface. The toothpick in your fruit experiment represented this distance.
If you think that the state of New South Wales is almost 2000 km across,
then you can appreciate just how far away these satellites are in space.
Even at this distance, geostationary satellites are nowhere near the moon
which is nearly ten times this distance away from the Earth.
For satellites to be held in a fixed position above the Earth, they must be:
•
close enough to the Earth to be held in orbit by the Earth’s
gravitational pull
•
far enough away from the Earth to prevent it from being pulled from
orbit to the Earth by the Earth’s gravitational pull.
This critical height above the Earth is called the high Earth orbit
(HEO). All geostationary satellites orbit the Earth in the HEO.
A geostationary satellite must orbit the Earth at the same rate as the
Earth rotates–one revolution in a 24 hour period.
Your fruit experiment demonstrated this rule–as the object at the end of
the toothpick (the geostationary satellite) finished in the same place it
began after a full rotation. In reality, this is a twenty four hour period of
rotation. If the satellite orbited the Earth any faster or slower than this,
the satellite would not be a geostationary satellite as it would not always
be in the same position above the Earth at any one time.
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Answer true (T) or false (F) to the following statements.
1
Geostationary satellites orbit the Earth.
T
F
2
Geostationary satellites orbit 2000 km above the Earth.
T
F
3
HEO stands for high Earth orbit.
T
F
4
Geostationary satellites must orbit the Earth in the HEO.
T
F
5
Satellites in HEO are pulled to Earth by gravity.
T
F
6
Satellites in HEO may float off into space.
T
F
7
A satellite is a man made object in orbit around a planet.
T
F
8
A geostationary satellite orbits the Earth once in 24 hours.
T
F
9
Geostationary satellites pass quickly across the sky at night.
T
F
10 In your experiment, the toothpick represents 36 000 km.
T
F
11 The large round piece of fruit represents a satellite.
T
F
12 The small object on the toothpick represents a satellite.
T
F
Check your answers.
Turn to Exercise 4.1 at the back of this part to locate the orbital area of
geostationary satellites.
Use of geostationary satellites
You should understand that satellites can be used to transmit or reflect
electromagnetic waves from one part of the world to another.
1
What do you think satellites that remain in a fixed position above
continents would be used for? Remember, this is a module about
Information systems, so try to relate your answer to the information
transfer systems you have studied.
_____________________________________________________
_____________________________________________________
_____________________________________________________
5
A geostationary satellites is in a fixed position above the Earth’s equator.
A geostationary satellite has a constant line of sight access to a specific
area of the Earth. The area of the Earth a geostationary satellite can send
and receive messages from is called a footprint.
The information transmitted to and from geostationary satellites includes:
•
live or commercial television programs
•
telecommunications
•
telephone conversations
•
digital information transfer
•
broadband internet access
•
video conferencing.
Often a single geostationary satellite carries out all the functions above
at once!
A ground level transmitting station transmits information such as a
television broadcast from America to a geostationary satellite at a
particular wave frequency. This is called the uplink. The satellite is
capable of receiving, amplifying and retransmitting the electromagnetic
wave to a target such as Sydney. Alternatively the satellite can receive
the wave, amplify it then change its frequency before sending back to
Earth. Either method can be used as a downlink from satellite to Earth.
For a satellite to alter an electromagnetic wave, it needs power.
You don’t hear about astronauts changing satellite batteries in space
because the big arms you see on satellites are actually covered in solar
panels. The panels absorb energy from the Sun, storing it as chemical
energy in rechargeable batteries for use during the night section of
the orbit.
Finish the following sentences based on the above information.
1
Three uses of geostationary satellites are ____________________
_____________________________________________________
_____________________________________________________
2
An uplink is ___________________________________________
3
A downlink is __________________________________________
4
Satellites have solar panels ________________________________
______________________________________________________
5
A geostationary satellite footprint is ________________________
______________________________________________________
Check your answers.
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Have you seen a satellite dish attached to a house? Does your home
have one? The following section explains the link between geostationary
satellites and satellite dishes.
Earth–based satellite dishes
Use the round fruit, toothpick and small object from the model you built
earlier in this part to complete the following activity.
1
The Appendix contains small pictures of satellite dishes. Turn to the
Appendix to cut out these five satellite dishes now.
2
Break three toothpicks in half.
3
On the same side of the round fruit that the original toothpick is sticking
out of, push the sharper end of five of the broken toothpicks deep into
the fruit, leaving around one centimetre of the toothpick exposed. This
can be done anywhere on the fruit, however it must be on the same side
of the fruit as the ‘satellite’.
4
Stick the five satellite dishes to the ends of the five broken
toothpicks with small balls of blutack or plasticine.
5
Manoeuvre each of the five satellite dishes so they are pointing
towards the satellite. Draw your model in the space below.
6
Rotate the piece of fruit through a full rotation (360°).
7
1
As you rotate the fruit (representing the Earth) through 360°, do the
satellite dishes remain facing the object at the end of the toothpick
(which represents the geostationary satellite)? Record your
observations.
______________________________________________________
______________________________________________________
2
Once Earth–based satellite dishes are aligned to have a line of sight
connection with a geostationary satellite, do they need to be moved
to account for the Earth’s rotation? Use your model to explain your
answer.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Satellite dish alignment
The diagram below shows how a satellite dish reflects waves from a
geostationary satellite to a receiver at a central point. The shape of the
dish is critical for the reflected waves to be focused to the receiver.
reflected waves
satellite dish
Electromagnetic waves being reflected and focused to a receiver by a satellite
dish.
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The Earth–based satellite dish needs to directly face the satellite to
receive clear reception. A clear reception is dependant on the intensity of
the waves hitting the dish. A dish must be calibrated at a right angle
(90°) to the waves entering the atmosphere for optimum reception. If the
dish is at another angle to the satellite, the intensity of the waves reaching
the dish would be reduced, therefore reducing the quality of reception.
receiver
satellite dish
waves from satellite
Electromagnetic waves reflected to a receiver by a satellite dish.
1
Is the above Earth–based satellite dish directly facing the satellite
(which is sending the waves)? How do you know this?
_____________________________________________________
_____________________________________________________
2
Is the Earth–based satellite dish above receiving a strong or weak
signal? Explain your answer.
_____________________________________________________
_____________________________________________________
receiver
satellite dish
waves from satellite
Satellite dish reflecting electromagnetic waves to a receiver.
9
3
Is the satellite dish on the bottom of the previous page facing the
satellite, which is sending the waves? How do you know this?
______________________________________________________
______________________________________________________
4
Is the satellite dish receiving a strong or weak signal? Explain your
answer.
______________________________________________________
______________________________________________________
5
If a satellite was sending a television signal to the satellite dish on
the previous page, explain why you would you expect the program to
be clear or fuzzy.
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Radio telescopes collect radio waves from space the same way satellite
dishes do. Radio telescopes are much larger as they need to collect
waves over a larger area to receive a signal from space. Radio telescopes
are moveable to receive waves from specific co–ordinates in space.
Satellite dishes differ from radio telescopes in that they are much smaller
and are designed to remain stationary for uninterrupted contact with a
specific geostationary satellite. Satellite dishes generally receive
telecommunications and television transmissions.
The only problem with geosationary satellites is a quarter of a second
time delay in information transmission. The distance of a geostationary
satellite above the Earth’s equator is 36 000 km. A wave travels around
70 000 km when transmitted to the satellite and back to Earth. It takes
around a quarter of a second for this to occur as electromagnetic waves
travel at 300 000 km per second. If information has to make two satellite
jumps, for information to reach the other side of the world, the time delay
is slightly longer.
To appreciate the importance of radio telescope dishes facing the direction
of the point source of waves, you might like to watch the movie The Dish as
an optional activity.
Turn to Exercise 4.2 at the back of this part to draw conclusions on satellites
used for live telecast to other regions of the world.
10
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Satellite orbits
Have you ever seen a satellite move across the sky at night?
These satellites are moving faster than the rotation of the Earth and are in
an orbit closer to the Earth. In fact there are several different orbits
satellites can be placed in depending on the use of the satellite.
Label the following on the diagram below.
1
The outer circle is the high Earth orbit (36 000 km from Earth).
2
The next circle in from the high Earth orbit is the medium Earth orbit
(10 000 km from Earth).
3
The two egg–shaped orbits are elliptical orbits.
4
The circular orbit closest to the Earth is the low Earth orbit (1000 km
from Earth).
Satellite orbits around Earth.
Check your answers.
11
Over 3500 satellites have been launched into space since the first
satellite, Sputnik, in 1957. You might be wondering why different
satellites use different orbits. There are several reasons.
•
Geostationary satellites must orbit in high Earth orbit due to the
gravitational forces. Because they are stationary with respect to the
Earth, uninterrupted television and telecommunication transmissions
can take place but with some time delay.
•
Medium Earth orbit satellites are also often used in land imagery,
telecommunications and weather forecasting. Telecommunications
often need to be transferred from satellite to satellite to maintain a
connection between widely separated ground earth stations.
Time delay in information transfer is insignificant at this height.
•
Elliptical orbits are similar to the orbit of a comet. This type of orbit
allows the satellite to travel closer to Earth, around 800 km above
the Earth, than the circular low Earth orbit satellites. A series of
satellites in elliptical orbits transmit television programs to Russian
homes and Canadian homes. These homes cannot be reached by
signals from geostationary satellites which are always above the
equator. The elliptical orbit satellites must travel at high speeds
when close to the Earth and are therefore not in range for long, so a
series of satellites with similar orbits must be used.
•
Low Earth orbit satellites are most commonly used for high
resolution land imagery and mobile telecommunications to and from
mobile phones, ships and aeroplanes. These satellites are travelling
at high speeds at a number of angles across the globe. One of a
group of around fifteen satellites is ensured to have line of sight
access to anywhere on the globe at any one time, however the
satellites must be tracked to change transmission from one satellite
to another without loss of the signal. A series of satellites used for
this purpose is called a constellation. Because these satellites are so
close to Earth, there is negligible time delay in information
transmission. The diagram below demonstrates the movements of
these low Earth orbit satellites.
A series of Low Earth orbit satellites (constellation) allow for global mobile
telecommunications.
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Imagine you are studying for a test. You are reviewing important
information you expect the examiners to include. What do you think the
examiners are likely to test for with regard to satellite orbits?
Examiners are likely to ask you to locate the different orbits, what
satellites in different orbits are used for and make a prediction such as
time delays for satellites in particular orbits.
Use a highlighter to highlight information on the previous page that is likely
to be examined in a test.
The next section deals with the components of satellites themselves.
Turn to Exercise 4.3 at the back of this part to complete a task on satellite
orbits.
13
Satellites
The satellite below has four main components:
•
solar panels
•
receiving aerial
•
electrical circuitry
•
transmitting aerial.
Guess where each of these labels above belong on the satellite below.
Hints: a bigger aerial is needed to receive waves from Earth; and the ‘arms’
are not aerials.
A typical satellite.
Check your answers.
Uplink information is transmitted from a ground station to the receiving
aerial in the form of electromagnetic waves. This information can range
from television broadcast or digital fax information to a phone
conversation or digitised Internet information. The wave is then boosted
and the frequency of the wave altered by electrical circuits in the
satellite. The downlink wave is then sent to a receiving station by the
transmitting aerial where the wave is then sent to its destination, such as
a home telephone.
Turn to Exercise 4.4 at the back of this part to interpret an Earth/satellite
diagram.
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Summary
As you complete the following find–a–word, think about the significance
of the words in relation to the information you have learned in this part.
Find the following words in the find–a–word below.
orbit
telecommunications
television
low earth orbit
downlink
right angle
constellation
solar panels
gravity
uplink
receiving aerial
twenty four hours
frequency
intensity
geostationary satellite
high earth orbit
electromagnetic wave
elliptical orbit
satellite dish
transmitting aerial
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15
16
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Appendix
17
18
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Suggested answers
Geostationary satellites
1
Geostationary satellites orbit the Earth.
T
2
Geostationary satellites orbit 2000 km above the Earth.
F
3
HEO stands for high Earth orbit.
T
4
Geostationary satellites must orbit the Earth in the HEO.
T
5
Satellites in HEO are pulled to Earth by gravity.
F
6
Satellites in HEO may float off into space.
F
7
A satellite is a man made object in orbit around a planet.
F
8
A geostationary satellite orbits the Earth once in 24 hours.
T
9
Geostationary satellites pass quickly across the sky at night.
F
10 In your experiment, the toothpick represents 36 000 km.
T
11 The large round piece of fruit represents a satellite.
F
12 The small object on the toothpick represents a satellite.
T
Use of geostationary satellites
1
Three uses of geostationary satellites are: live television
transmissions; telephone conversation transmission and internet
broadcasting. Other answers are acceptable.
2
An uplink is the transmission of a wave to a satellite at a particular
frequency.
3
A downlink is the transmission of a wave from satellite to Earth at a
particular frequency.
4
Satellites have solar panels to absorb energy for use in boosting and
altering wave frequencies.
5
A geostationary satellite footprint is the area of the Earth a
geostationary satellite can send and receive messages from (line of
sight).
19
Earth–based satellite dishes
1
As the fruit (Earth) rotates through three hundred and sixty degrees,
the satellite dishes remain facing the geostationary satellite because
the satellite does not move relative to the Earth.
2
Once satellite dishes are aligned to have a line of sight connection
with a geostationary satellite, they do not need to be moved to
account for the Earth’s rotation. The model shows that once a
satellite dish is calibrated to have a line of sight connection with a
satellite, it will maintain that calibration throughout the Earth’s
rotation.
Satellite dish alignment
1
The satellite dish is directly facing the satellite, which is sending the
waves because all the waves hitting the dish are being reflected to
the receiver and the dish is at right angles to the waves.
2
The satellite dish is receiving a strong signal because waves from the
satellite are being reflected from the entire dish to the receiver and
the dish is at right angles to the waves.
3
The satellite dish is not directly facing the satellite because the dish
is not at right angles to the waves and waves are not hitting the entire
dish.
4
The satellite dish is receiving a weak signal because waves are not
hitting the entire dish for reflection to the receiver, cutting down on
the energy received.
5
If a satellite was sending a television signal to this satellite dish the
program would be fuzzy because the dish is not detecting all the
waves it could, resulting in a weak signal.
Satellite orbits
low Earth orbit
(1000 km)
eliptical orbits
Earth
medium Earth orbit
(10 000 km)
high Earth orbit
(36 000 km)
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Satellites
receiving aerial
solar panels
electrical circuitry
transmitting aerial
Summary
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A
Q
U
E
N
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22
Information systems
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Exercises - Part 4
Name: _________________________________
Exercise 4.1
The following diagram of a geostationary satellite in orbit above the
Earth is missing three labels. Use the information from pages 3 to 5 to
complete these labels.
km
2
Give two reasons why geostationary satellites must orbit in the high
Earth orbit region.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
23
Exercise 4.2
The diagram below shows a satellite positioned to send and receive
messages from two countries. It provides for live telecast of television
programs, telephone conversations, digital information transfer and
videoconferencing between these two countries.
Satellite with two footprints for live telecast between countries.
1
Explain why the satellite used for live telecast in the above diagram
is likely to be a geostationary satellite.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
2
Explain why geostationary satellites are positioned above the
equator.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
24
Information systems
high Earth orbit
Satellite orbit
elliptical path;
can travel within
800 km of the
Earth
10 000 km
above Earth
Orbit
height/style
high resolution land images;
mobile telecommunications
with mobile phones, ships
and aeroplanes
Satellite use
insignificant time delay;
satellites transmission
changes from satellite to
satellite as individual
satellites move out of range
Orbital features (time delay,
satellite speed and tracking)
Gill Sans Bold
Exercise 4.3
Complete the missing information in the table below on satellite orbits.
25
Exercise 4.4
The diagram shows a satellite in use. In the space provided, write a
paragraph explaining what is happening in the diagram from the
originating ground station to the destination ground station. Be sure to
identify the differences between the transmitting and receiving aerials in
your paragraph.
receive aerial and receiver
originating
ground
station
transmit aerial and transmitter
destination
ground
station
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
26
Information systems
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Senior Science
HSC Course
Stage 6
Information systems
Part 5: Information through impulse
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Lifestyle chemistry
Information systems
•
Get the message?
•
Waves waves waves
•
More waves
•
Messages from space
•
•
Fibre optics
Option
Gill Sans Bold
Contents
Introduction ............................................................................... 2
Coding and decoding information.............................................. 3
Energy transformations ............................................................. 7
Electrical impulses..................................................................... 8
Generating electrical impulses ............................................................9
Summary................................................................................. 12
Exercises–Part 5 ..................................................................... 19
1
Introduction
Part 5 places information that you have learned through Parts 1–4 in
context. You will identify the energy transfers involved in coding and
decoding information by the digital technologies.
•
identify communication technologies that transform one type of
energy into electrical energy
•
describe the transmission of images using digital technologies in
terms of scanning of the input image along very thin lines
•
explain how the coding of the image into a series of zeros and ones
allows its transmission and ultimate decoding
In this part you will be given opportunities to:
•
gather, process, analyse and present information from secondary
sources to identify energy transfers involved in coding and decoding
information by digital technologies.
2
Information systems
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Coding and decoding information
Most modern communication systems transfer information using digital
technologies.
Coding converts information into binary coded form which uses the
digits 0 and 1. The digital transmission is by electrical, light or
electromagnetic impulses representing the 0s and 1s. Decoding changes
the 0s and 1s impulses received back to information which can be
understood by the receiver.
Digitised information is very resistant to interference and noise:
digitised signal
plus noise
equals modified digital signal – but it
is still clear whether the value is a one
or a zero
1
0
3
In this section you will gather, process, analyse and present information
from audio tape/internet files. The audio files, and diagrams supplied in
this print material, should help you identify the energy changes involved
in coding and decoding information using digital technologies.
You can become better informed by using the audio files on faxes (an
abbreviation for facsimiles), computer–based information systems and
emailing and internet.
Faxes (Facsimiles)
Use the faxes section of the Information systems audiotape/internet audio
files to answer the following questions on fax machines.
Fill in the missing words in the following sentences.
1
Fax information is optically _________________ along very thin
_________________ across the page.
2
A page is broken up into a _________________ consisting of very
small _________________.
3
The scanner records the number _________________ in the box
when scanning a dark section and a _________________ when
scanning a white section.
4
This light energy information is transformed by a photodiode into
_________________ energy and sent along phone lines.
5
The receiving _________________ machine puts
_________________ in the small grid boxes with ones and leaves
the boxes with zeros _________________.
6
Colour in the following boxes labelled with the number ‘1’ and leave
the boxes with the number ‘0’ blank. Complete the first row first,
then move to the next row and so on.
What message is being sent?
4
0
0
1
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
1
1
1
0
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
0
1
1
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
1
1
1
0
0
0
Information systems
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You just decoded a fax message in a similar way to a
fax.
Check your answers.
Computer–based information systems
When a computer uses the telephone system to communicate with
another computer a modem (abbreviation for modulator/demodulator) is
used between the computer and the transmission line. An external
modem lies outside the computer while an internal modem is inside
the computer.
If you send an email or use the internet you will be using a modem to
facilitate transmission of your data.
Use both the computer–based information systems and emailing and
Internet sections of the Information systems audiotape/internet audio files
before answering the following questions.
1
In the grid below, colour in the boxes with on written in the box and
leave the boxes with off blank. What letter does this code of ons and
offs make?
off
off
on
off
off
off
off
on
on
on
off
off
off
off
on
off
off
off
off
off
on
off
off
off
off
off
on
off
off
off
off
off
on
off
on
off
off
off
on
on
off
off
5
Answer true (T) or false (F) to the following questions.
2
3
4
5
6
Email and Internet information may be sent along phone lines
without modems.
____
Computer information is stored digitally as a series of zeros and
ones in the random access memory.
____
Modems send coded digital information as ones and zeros, each
at different frequencies down phone lines.
____
Modems can only send digital information, not receive and
decode information.
____
Computer based information systems uses electrical energy to
transfer information.
____
Check your answers.
6
Information systems
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Energy transformations
Parts 1 and 5 have outlined the energy transformations involved in
information transfer in various information systems. You should now be
able to identify the different energy transfers involved in each type of
information system.
Complete the following activity to refresh your memory.
Match the following information systems with the basic energy
transformations involved in each by writing one of the following
information systems on the blank lines below:
sound system; radio receiver; mobile phone; television receiver;
telephone; and facsimile.
impulses
elec
trical
t
elec beam of electro
r
o
ma
ns)
(
rgy
gn
sound
e
ene
ic
lig tic
ht
es inet ulses
(ink going o
k
e
p
nto
im
p
gy
ap
al ner
sound
er
e
)
sound
ic )
es s
lse
sound
electrical impulses
elect
rom
a
electrica
l im gnet
p
u
electrical or light energy + kinetic energy
lse ic w
s
av
optical energy
electrical impulses
ele
ctr
sound
electrical impulses (and lig
ht i kine ic
m
t
electromagnetic energy
electrica
p
l im uls
pu
s
ve
wa gy
r
ne
rical impulses
elect
sou
nd
Turn to Exercise 5.1 at the back of this part to identify communication
technologies that transform different energies into electrical energy.
7
Electrical impulses
You should appreciate that a page being faxed is optically scanned and is
recorded as a series of electrical impulses of ones and zeros or ons and
offs, which are transmitted down telephone lines to a receiving fax
machine. The receiving fax machine places ink in the grid where it
receives an on or one signal and leaves blank areas when it receives an
off or zero signal.
1
Explain how a page is broken up for scanning by a fax machine.
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
Given that digital ons and offs or zeros and ones have different
frequencies and a faxed page is transmitted through phone lines in
this way, explain how a fax machine prints an almost identical copy
of the original page with this digital pulse information.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Turn to Exercise 5.2 at the back of this part to complete a task on digital fax
transmissions.
8
Information systems
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Generating electrical impulses
You are familiar with electrical energy. You know that if you turn on a
light, electrical energy is converted to light energy by the light globe.
You should also know that electrical energy is essentially converted to
sound energy for you to listen to your stereo. Common household
energy transformations like these convert electrical energy into another
form of energy. Have you ever thought of changing one form of energy
into electrical energy?
When you use batteries in your camera, walkman or remote control car,
you are changing chemical energy from the batteries into electrical
energy. This electrical energy is then used to wind on the film, play your
music or move the remote control car’s wheels.
When you use a microphone, sound energy is converted into an electrical
signal. When an aerial receives radio waves, it converts these waves into
an electrical signal. Power stations burn coal to heat water, which
produces steam. The kinetic energy of the steam turns turbines which
turn generators to produce electricity, thus turning kinetic energy into
electrical energy. Hydro–electric schemes also use the kinetic energy of
water to produce electricity. These are all common examples of
changing one form of energy into electrical energy.
Think about the different forms of energy that are changed into electrical
energy at some stage in different information technologies.
1
Mobile phones and telephones change what form of energy into an
electrical signal?
_____________________________________________________
2
Televisions and radios change what form of energy into electrical
signal?
_____________________________________________________
3
Fax machines and long distance telephone lines (optical fibres) convert
what form of energy into electrical energy?
_____________________________________________________
Check your answers.
Computer based communication systems change electrical energy into
impulses of electrical energy representing zeros and ones for emailing and
internet information transfer through telephone lines.
9
The Electrical impulse section of the Information systems audiotape explains
the following diagrams and what each experiment is expected to show.
Listen to and complete the activities outlined on this section of the
audiotape.
microphone
1
cathode ray oscilloscope
wire
Sound energy converted to electrical impulses.
2
battery
wire
tapping key open
(open circuit)
voltmeter
(multimeter)
Tapping key open preventing flow of electricity through the circuit.
battery
wire
tapping key closed
(closed circuit)
voltmeter
(multimeter)
Tapping key closed allowing flow of electricity through the circuit.
10
Information systems
Gill Sans Bold
3
needle alternates
between these two
positions
wire coil
magnet
wire
microammeter
(multimeter)
Magnet moving into and out of a wire coil.
Check your answers.
11
Summary
Use a mind map approach to surround the following syllabus points with
the relevant information you have learnt throughout this part.
identify communication
technologies that transform
one type of energy into
electrical energy
describe the transmission
of images using digital
technologies in terms of
scanning of the input
image along very thin lines
12
Information systems
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explain how the coding
of the image into a
series of zeros and ones
allows its transmission
and ultimate decoding
gather, process, analyse
and present information
from secondary sources
to identify energy
transfers involved in
coding and decoding
information by digital
technologies
13
14
Information systems
Gill Sans Bold
Suggested answers
Faxes (Facsimiles)
1
Faxes information is optically scanned along very thin lines across
the page.
2
A page is broken up into a grid consisting of very small boxes.
3
The scanner records the number one in the box when scanning a dark
section and a zero when scanning a white section.
4
This light energy information is transformed by a photodiode into
electrical energy and sent along phone lines.
5
The receiving fax machine puts ink in the small grid boxes with ones
and leaves the boxes with zeros blank.
6
0
0
1
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
1
1
1
0
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
0
1
1
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
1
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
1
1
1
0
0
0
Computer based information systems
1
o
n
o
n
o
n
o
n
o
n
o
n
o
n
o
n
o
n
o
n
o
n
15
2
Email and Internet information may be sent along phone lines
without modems.
F
3
Computer information is stored digitally as a series of zeros and
ones in the random access memory.
T
4
Modems send coded digital information as ones and zeros, each
at different frequencies down phone lines.
T
5
Modems can only send digital information, not receive and
decode information.
F
6
Computer based information systems uses electrical energy to
transfer information
T
Energy transformations
sound
electrical impulses
elect
rom
a
electric
al im gnet
ic
pul
electrical or light energy + kinetic energy
se
wa
s
v
optical energy
electrical impulses
ele
ctr
sound
electrical impulses (and lig
kin ic
ht
electromagnetic energy
electrica impu et
l im ls
pu
mpulses
trical i
elec
elec
t
r
o
beam of electrons
ma
)
rgy (
gn
ene
sound
e
tic
lig tic
es kine ulses
ht
(ink going o
p
nto
e
im
p
gy
ap
al ner
sound
er
e
)
sound
ic )
es s
lse
s
ve
wa gy
r
ne
rical impulses
elect
mobile phone
television receiver
sound system
facsimile
telephone
radio receiver
sou
nd
Electrical impulses
16
1
A page is broken up for scanning by a fax machine into a fine grid.
Light and dark information on the page is recorded in this grid.
2
An on pulse frequency for a particular grid co–ordinate causes a fax
machine to place ink on paper in that grid space. An off impulse
frequency causes the fax machine to leave the grid co–ordinate
blank. This process occurs a large number of times to form an
almost identical copy of the original page.
Information systems
Gill Sans Bold
Generating electrical impulses
1
Mobile phones and telephones change sound energy into electrical
energy.
2
Televisions and radios change electromagnetic energy into electrical
energy.
3
Fax machines and long distance telephone lines (optical fibres)
convert light energy into electrical energy.
1
microphone
cathode ray oscilloscope
wire (carrying electrical impulse)
2
battery
wire
tapping key
(electrical
closed
impulses carried (closed circuit)
in wires)
voltmeter
(multimeter)
3
needle alternates
between these two
positions
wire coil
(electrical
impulse)
magnet
wire
(electrical
impulse)
microammeter
(multimeter)
17
18
Information systems
Gill Sans Bold
Exercises - Part 5
Name: _________________________________
Exercise 5.1
For four information technologies, record the energy type that is
transformed into electrical energy. You may use the information on
page 6 to help you with your answer. A form of energy changed into
electrical energy for mobile phones has been done for you as a guide.
Information technology
Energy type before transforming
into electrical energy
mobile phone
sound energy
19
Exercise 5.2
1
Explain the energy conversion involved in sending a fax by a fax
machine.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
2
What information is sent through telephone lines to the receiving fax
machine?
______________________________________________________
______________________________________________________
______________________________________________________
3
Explain how the receiving fax machine interprets the information
sent through the telephone line in order to print a copy of the original
fax.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
20
Information systems
Gill Sans Bold
Senior Science
HSC Course
Stage 6
Information systems
Part 6: Fibre optics
2
0
0
I
2
r
be S
o
t
c NT
O
ng DM E
i
t
ra E N
o
rp A M
o
nc
Lifestyle chemistry
Information systems
•
Get the message?
•
Waves waves waves
•
More waves
•
Messages from space
•
•
Fibre optics
Option
Gill Sans Bold
Contents
Introduction ............................................................................... 2
Bending light ............................................................................. 3
Total internal reflection.........................................................................4
Optical fibres ............................................................................. 8
So what is an optical fibre?................................................................10
Copper cables and optical fibres .......................................................14
Australian research in fibre optics ........................................... 17
Appendix ................................................................................. 19
Sue Spaargaren .................................................................................19
Exercises–Part 6 ..................................................................... 27
Bibliography ............................................................................ 33
1
Introduction
Part 6 outlines the principles of information transmission through optical
fibres. You will learn how light can follow the twist and turns of optical
fibre without escaping and compare the efficiency and carrying capacity
of copper cables against optical fibres in telecommunications.
•
outline properties of optical fibres as communication carriers
•
outline the principle of total internal reflection and relate this to the
advantages of fibre optics over more conventional carriers of
information
•
outline the differences and relative merits in the use of fibre optics
cables and metal cables to transmit and receive information.
In this part you will be given opportunities to:
•
perform a first–hand investigation to demonstrate the transmission of
light through an optical fibre
•
process and analyse information from secondary sources to compare
and contrast copper cables with fibre optic cables in relation to
–
carrying capacity
–
cost
–
rate of information transfer
–
security.
Although light can pass through optical fibre and is used in these
notes and activities about optical fibre, most of the electromagnetic
radiation used in modern optical fibre communication systems is
infra red radiation with a frequency about half that of red light.
2
Information systems
Gill Sans Bold
Bending light
The following activity is best done at night, however you may observe
the results in a darkened room during daylight.
Read through the following instructions first to identify the equipment
you will need to complete the task.
1
Collect a medium to large old glass jar with a lid.
2
Use a hammer and nail to punch two holes in the lid on opposite edges
of the lid. One hole should be small and the other hole should be larger.
Try to use a thin and a thicker nail to make clean circular holes.
3
Three quarters fill the jar with water and place the lid on top firmly.
4
Use small pieces of sticky tape to cover the holes on the surface of
the lid to stop water leakage.
5
Lie the jar on its side on the kitchen sink or on an outside bench.
The larger hole in the lid should be closest to the sink or bench.
You may need to support the jar to prevent it from rolling. Be aware
that water will be coming out of the large hole in the lid–so set up
the apparatus so it doesn’t make a mess.
6
Turn on a torch and place the torch face at the base of the jar as
shown below. Again, you may need to support the torch to prevent
it from rolling.
small hole
in lid
torch
large hole
in lid
jar
Torch facing the base of a glass jar.
7
Cover the torch and jar with a dark towel so only the jar’s lid is
exposed.
8
Remove the sticky tape covering the holes and observe, using your
observations to answer the following questions.
3
1
What do you notice if you place your finger in the stream of water in the
places shown in the following diagram?
place your finger in
the stream of water
in these three places
glass jar
jar lid
torch
water
stream
of water
_____________________________________________________
_____________________________________________________
2
Is the light from the torch held completely within the stream of water or
does the light shine straight through the lid hole as if the jar was empty?
_____________________________________________________
3
Can you suggest why light, which travels in straight lines appears to
bend in this experiment?
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
The following section explains the phenomenon you just observed.
Total internal reflection
Despite what you witnessed in the previous experiment, light always
travels in straight lines. Light is part of the electromagnetic spectrum.
Do you remember studying the reflective properties of electromagnetic
waves in Part 3? You should recall the diagrams showing radio waves
bouncing off layers in the atmosphere and waves being reflected by
satellite dishes. Light is no exception to this rule of reflection.
You might be baffled as to how light appears to curve in a stream of
water if it is true that light only travels in straight lines. The answer lies
in total internal reflection.
4
Information systems
Gill Sans Bold
Each diagram below shows a beam of light travelling from a relatively
dense medium such as glass to a less dense medium such as air.
The dotted line down the centre is an imaginary line perpendicular to the
surface of the glass called the normal. This line is used to measure the
angles of light beams. The angle between the normal and the entering
light beam is called the incident angle.
1
For each of the diagrams below use a ruler and a pencil to join dots B
and C, then draw an arrow on the line indicating the direction of the
light.
normal
a)
less dense
medium
for example air
.C
B
more dense
medium
for example glass
b)
less dense
medium
for example air
normal
A
.C
B
more dense
medium
for example glass
c)
less dense
medium
for example air
normal
A
B
more dense
medium
for example
glass
A
.
5
2
Explain what happens to the beam of light from B to C in diagram
a) on the previous page. Indicate if it moves into a more dense or
less dense medium and if its angle changes or not.
______________________________________________________
______________________________________________________
3
Look at the angle of the light line between the line A to B and the
normal in diagram a) (the incident angle). Is this angle smaller or
larger than the same angles in the other diagrams?
______________________________________________________
4
Explain what is happening to the light line from B to C in diagram
on diagram b) on the previous page. Be sure to identify if it leaves
the denser medium or not.
______________________________________________________
______________________________________________________
5
Does the line B to C have a different angle to the normal than the
line A to B in diagram b)?
______________________________________________________
The angle between A and B and the normal in diagram b) is called
the critical angle. This means the angle at which the beam of light
will travel along the edge of the denser medium.
6
Is the angle between the light line from A to B and the normal in
diagram b) (the incident angle) larger or smaller than diagram a)?
______________________________________________________
7
Explain what is happening to the light line from B to C in diagram
c) on the previous page. Indicate which medium it moves into.
______________________________________________________
______________________________________________________
8
The light line from A to B on diagram c) is being reflected back
inside the glass. Is the angle between A to B and the normal (the
incident angle) greater or smaller than the first two diagrams?
______________________________________________________
9
Look at the angles between A and B and the normal and B and C and
the normal in diagram c). Are these angles the same or different?
You may use a protractor to be sure.
______________________________________________________
Check your answers.
6
Information systems
Gill Sans Bold
Light travelling from a denser medium to a less dense medium
exceeding the critical angle is totally internally reflected and
stays within the denser medium.
All the above statement means is that at whatever angle light travels in
the glass above the critical angle, the light will always be reflected back
inside the glass. This is shown in the diagram below.
result of critical angle
angles greater
than the
critical angle
critical
angle
total internal
reflection
light beam at
critical angle
Total internal reflection of light inside a tube of glass. Light at an angle greater
then the critical angle is totally internally reflected.
Long, thin cylinders of glass called optical fibres use the principles of
total internal reflection for information transmission.
7
Optical fibres
The following activity demonstrates how light travels through optical fibres.
1
Join the points A, B, C, D and E on the first optic fibre below.
2
Join the points A, B and C on the second optic fibre below.
3
Join the points A, B, C and D on the third optic fibre below.
A
A
A
optic fibre 1
air
optic fibre 2
air
optic fibre 3
(more
(less dense)
(more
(less dense)
(more
dense)
dense)
dense)
B
B
C
C
D
B
E
8
C
D
Information systems
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Reconstruct the following sentences.
4
total through Light fibres by reflection. travels optic internal
_____________________________________________________
_____________________________________________________
5
optical angles light walls. reflect off Different fibre of
_____________________________________________________
_____________________________________________________
Check your answers.
Remember the digital information that is sent along telephone lines
(as ons and offs or zeros and ones)? Many telephone systems use light
waves in optical fibres to carry this digital information.
A light wave travelling through an optical fibre can represent the ons and
offs or zeros and ones information. The on or one light signal has a
different frequency than the off or zero light signal. Your voice is
converted to these digital impulses to travel at the speed of light through
long distance telephone lines.
Digital fax information, internet information and email information all
travel the same way through optical fibres in telecommunications
networks.
You might be wondering how your voice gets transmitted as light signals
along optical fibres. Remember–the sound of your voice is just a form of
energy. This energy is converted to light energy which represents the
way you speak. When the light energy reaches its destination, it is
converted back to sound energy. Digital computer based information is
changed to light energy and back again in a similar way.
9
So what is an optical fibre?
An optical fibre is a strand of material (commonly glass fibre)
through which light or infra–red radiation can travel.
The diagram below shows thin strands of plastic optical fibres on the end
of a torch.
Optical fibres carrying light from a torch.
As you can imagine, a long thin strand of glass the thickness of a hair is
not very strong. For this reason, optical fibres require cladding.
The cladding needs to be of lower refractive index than the strand of
glass to ensure total internal reflection within the glass fibre.
There are three main types of optical fibres used for telecommunications.
Multimode optical fibre
total internal reflection
of several light impulses
within the optic fibre
cladding with lower
refractive index
than optical fibre
optic fibre
light entering
cladded optical
fibre
Multimode optical fibre.
10
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Thousands of different digital transmissions may be sent along a
multimode optical fibre. The light impulses are often sent in the
infra–red band of the electromagnetic spectrum. The glass inside the
cladding has a consistent refractive index throughout the fibre.
Graded optical fibre
optic fibre has a graded
density causing light to travel
faster on the edges of the
fibre than the centre
cladding with lower
refractive index or
optical density
than optical fibre
graded optic fibre
Graded optical fibre.
Imagine running 100 metres, but instead of running in a straight line, you
zig–zagged across the track to the finish line. Would you have travelled
further than if you had run in a straight line? Of course you would have.
Light impulses bouncing off the edges of an optical fibre would also
travel much further than light that barely touched the edges. This causes
impulses to arrive at their destination at slightly different times.
Graded optical fibres have a higher refractive index material towards the
centre of the fibre. The refractive index gradually decreases towards the
outer edges of the fibre. This causes light inside the optical fibre to
appear to curve, although light is still travelling in a straight line.
The result of graded optical fibres is all the light transmissions,
regardless of how many times they are internally reflected, arrive at their
destination at the same time. This prevents time delays in transmission.
Quality of output information is better than for the multimode optic fibre.
11
Small diameter core
small diameter core optical fibre (3–5 mm)
cladding
Small diameter core.
The glass strand inside this optical fibre is only 3–5 µm (3 –5 x 10–6 m)
in diameter and only transmits a single impulse at any one time.
Only one light wave can fit inside the inner core at one time. An impulse
of light travels through the high refractive index material centre.
Because there is no interference with other waves and the light contained
inside the core cannot spread out due to the size of the core, the quality of
the information transmitted is excellent and does not need to be boosted
for 500 km. Small diameter optical fibres are therefore often used in
long distance cables, however the precision lasers required to beam the
impulses through these fibres and the technology required to align
their tiny cores cause them to be more expensive than other optic
fibre varieties.
1
What is the difference between a multimode optic fibre and a graded
optic fibre?
_____________________________________________________
_____________________________________________________
2
Why is an optic fibre strand encased in cladding?
______________________________________________________
______________________________________________________
3
What problem does graded optical fibre attempt to overcome?
______________________________________________________
______________________________________________________
12
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4
Which type of optical fibre is more effective in long distance
telecommunications and why?
_____________________________________________________
_____________________________________________________
You have identified a glass strand and its cladding however optical fibres
are surrounded by several more layers for strength and durability.
5
6
Label the diagram below with the following:
•
the thinnest tube is the glass core and cladding combined;
together they form the optical fibre
•
the next layer is silicone
•
the next layer is the buffer jacket
•
the second last layer is the strength layer
•
the outside layer is polyurethane
Label the above diagram as a single optical fibre.
Check your answers.
Even with the protective layers, optical fibres are quite flexible.
Rarely is one optical fibre laid alone in telecommunications. Bundles of
optical fibres such as the one above are usually encased inside a cable in
telecommunications.
Turn to Exercise 6.1 at the back of this part to summarise the properties of
optical fibres.
13
Copper cables and optical fibres
Copper cables are still used in telecommunications for local networks.
Instead of your voice being changed in to light impulses, it is changed
into electrical impulses at different frequencies for transmission along
copper cables.
The advantages optical fibres have over copper cables are outlined
below.
•
Optical fibres carry information at the speed of light, allowing more
information transmission in one cable than transmission by electrons
in electric signals in copper cables.
•
Optical fibres totally internally reflect light impulses, therefore less
energy is lost and information is more precisely transmitted than in
copper cables which can distort signals and lose energy in the form
of heat due to electrical resistance in the wire. Optical fibres
therefore allow for greater clarity in information transfer.
•
Thin optical fibres made of glass are much lighter than the thicker
copper cables needed to carry the same volume of information.
Thousands of conversations can be transmitted through a series of
copper cables with the diameter the size of a tennis ball or by a
single optical fibre with the diameter of a strand of hair.
•
Glass in optical fibres is more corrosion resistant than copper cables.
•
Due to the nature of optical fibres and total internal reflection,
optical fibres are totally secure as they cannot be tapped.
Copper cables are less secure as electrical information can be
re–routed through wires and therefore tapped.
•
Copper cables and optical fibres costs are roughly the same, however
copper cables require repeaters to boost signals every 1.5 km.
Optical fibres require repeaters every 100 km therefore optical fibres
are cheaper overall.
All this means that when you talk on your home telephone, dial up the
Internet from home or receive a fax, the last place the information has
been before reaching the telephone, computer or fax is a copper wire.
There are three main reasons for this.
14
•
Fibre optics is a relatively new technology. Houses and businesses
were already networked to telephone exchanges with copper wiring
prior to the invention of optic fibres.
•
Most telephones, computer modems and fax machines are only able
to convert analog electrical impulses from wires to a useable form.
This means that fax machines, telephones and modems are not
capable of changing light impulses from optical fibres to the required
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type of electrical energy, so a decoder must complete this digital to
analog conversion at a telephone exchange.
•
The majority of telephones, fax machines and modems are designed
to transmit information as analog electrical impulses through wires.
A coder must transform analog electrical impulses to digital
impulses for transmission through telecommunication networks.
Information can be transmitted and received over short distances quite
well through copper wires. Digital information from optical fibres is
decoded and converted to analog electrical pulse information for
transmission into homes and businesses through copper wires as shown
on the following page.
Collect some coloured pencils to complete the following activity using the
diagram on the following page.
1
Colour the copper wires that transmit analog electrical impulses red in
the diagram on the following page.
2
Colour the copper wires that transmit digital electrical impulses purple.
3
Colour the optical fibres yellow.
4
Colour the light detector orange.
5
Colour the repeater light blue.
6
Colour the light source light green.
7
Colour the coder dark blue.
8
Colour the decoder dark green.
15
l im
re
wi
ic a
er
c tr
pp
e le
co
g
pu
l im
ic a
c tr ir e
e le r w
e
pp
co
an
ls e
a lo
g
pu
a lo
ls e
an
coder
decoder
l impu
ctrica
le
e
l
digita
r wire
co p p e
lse
dig
ital e
le
c
t
r
ical im
pulse
co p p e
r wire
light source
d ig
light detector
ita l
opt
ic a
l fi b
lig h
r
t im e
pul
se
repeater
ib re ls e
al f
c
pu
i
t
op
t im
h
g
li
i ta l
d ig
Energy transformations through telecommunication lines.
Turn to Exercise 6.2 at the back of this part to outline the advantages of
information transfer in optical fibres.
16
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Australian research in fibre optics
The Appendix contains information on a practising female scientist in the
fibre optics field. Use the information in the Appendix to answer the
following questions.
1
What is the name of the practising female scientist?
_____________________________________________________
2
What qualifications does she have?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
3
What is she researching?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Answers are not supplied for this activity to encourage you to complete
the task.
17
18
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Appendix
The following information is accessed from: Spaargaren, S.M.R. Western
Australian Women in Science. Sue Spaargaren.
<http://www.swimwithdragons.com.au/cgi–bin/cgiwrap/dragons/allegro.pl?wis
_search.Sue+Spaargaren> (accessed 28 November 2000).
Sue Spaargaren
University of Western Australia, Department of Electrical and Electronic
Engineering.
Age
33
Qualifications
Bachelors: B Eng (Hons) Electrical and Electronic
Engineering. Masters: M Sc Microwaves and
Optoelectronics. Doctorate: PhD Electrical
Engineering on "Radiation Effects in Silica based
Waveguides" (optical fibre related).
School science
subjects
Maths, Physics, Chemistry
Main science
discipline
Physics
Place of work
University
A typical day at work
My job involves planning, performing and writing up experiments on
optical communications. In this field, lasers are used to send light pulses
along "optical fibres" (a type of thin glass light 'pipe'). The laser light is
picked up at the far end by an electronic light sensor
(‘photodetector’ or electronic 'eye').
19
This method is used today to send telephone calls across long distances
and to send messages between some computers. It is better to use light
pulses in fibres for these applications (rather than electronic pulses in
wires) because light pulses transmit information much faster.
In the future, people also want to use optical fibres to speed up
connections between electronic circuit boards inside very fast 'parallel'
computers and inside big switches in telephone exchanges.
My work involves testing a new type of light sensor for these
applications, which can be set to 'see' different laser colours. The more
colours that it can see, the faster the connection will be (i.e. the more
phone calls will be transmitted at once). I use different types of
microscopes and light experiments to test how well the electronic eyes
are working. I then try to use the results from these experiments to help
the people I work with, who make the sensors, to improve the design of
the next batch. So far, we have found that the composition and shape of
the sensor both affect the number of colours seen.
Sometimes I work on my own and sometimes I work with other people
working on the same or similar projects. A typical day involves some
planning, or setting up, or performing of experiments. It also involves
some reading in the library (to keep up with the research being done by
other people around the world) and some discussion with other people at
uni about future experiments. Looking at the results from previous
experiments and writing about them on a computer is also an important
part of my work. When the results have been written up, we send them
to be published in research journals, so that other people around the
world can see what we have been doing. From time to time I also do a
bit of teaching on optical communications.
The best aspects of my work
I enjoy the variety of work and the mixture between working on my own
and working with other people (some of whom are very experienced and
teach me a lot). I like always learning new things from other researchers
and the excitement of occasionally getting new results that no–one in the
world has ever got before (after months of hard work on difficult
experiments). Then there is the flexibility of research work which means
that although you work mainly office hours, sometimes you are extra
busy and have to work in the evenings or at weekends, whereas
sometimes you are less busy and can leave work early. When I teach I
enjoy meeting students and explaining to them how lasers, optical fibres
and light sensors work.
20
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Personal qualities required for my job
For my job you need to be a curious person who enjoys trying to
understand how things work. You also need to like doing detailed work
and be quite a patient person, as often it takes quite a long time between
starting a new experiment and getting good results. You also need to be
good at organising your own time when you are working alone, but like
working with other people as well sometimes.
How I got to be doing the job I am doing
Since both of my parents were scientists, we were always having
interesting discussions about science at home when I was growing up in
the UK. I enjoyed studying science and maths at school, so I decided to
specialise in these subjects in my last two years at high school.
My parents then encouraged me to go to university to help me get a good
job later. I decided I wanted to study a subject at university which uses
maths and science to solve practical problems–engineering. I chose to
study electrical and electronic engineering because I felt it was the most
exciting and rapidly changing of the engineering subjects and also
because I knew I would learn quite a lot of computing skills, which I
thought I would enjoy and would be very useful for getting a job later on.
Just before the last year of my Bachelors degree, I spent a summer in
France writing computer programs to help researchers there understand
the results from their optical fibre experiments and became fascinated by
this field. In the end, I decided to study this area further, so I continued
at uni after my Bachelors degree with a Masters degree. After this, I
decided I really wanted to do some full–time research and so I carried on
for several more years to do a PhD on a particular aspect of optical
communications.
About a year ago and a half ago I moved to Western Australia from
the UK. Then I took a holiday for a few months and after that, about a
year ago, I was offered the job I am doing now at the University of
Western Australia.
Role models
As with a lot of daughters, my father was probably the most influential
person in my life. He was an electronic engineer and encouraged me
(and my brother) to discuss scientific ideas (like how the planets orbit the
sun) at home after tea when we were young. Later he encouraged me in
my studies even when I was finding it difficult and was always interested
to know what I was doing.
21
My mother also encouraged me as she is a biologist and is quite unusual
for her generation because she also studied science at university. She is a
great role model as she is proof that women can be both successful in
science and have a good home life too.
I also had some very good science and physics teachers at school.
Particularly my physics teacher, Mr Miller, in the last two years of
school, who made us work really hard, but told us we could all get top
marks if we tried hard enough. He was very good at explaining the logic
behind physics questions and made the lessons really interesting.
Work ambitions
My work ambitions at the moment are to get as many good results and
publish as many papers as I can and do a good job of teaching, while I
gain more research experience. After a few more years experience,
I would like to either become a lecturer at university or work in industry
as a manager of a research team.
My other interests outside work
I like swimming, snorkelling, aerobics and singing for fun and have
recently started scuba diving, mainly off Rottnest. My husband and I
also enjoy travelling around the state to explore new places. We really
like visiting the Margaret River area and have also explored Albany,
Augusta and Karinjini National Park (near Port Hedland), as well as
Geraldton, Kalbarri and the Abrohlos Islands (near Geraldton).
Being female and working in science
Being female in science has never been a problem for me and is
sometimes a positive advantage. For example, anything that makes
you different means that people tend to remember you better, so it can be
useful in making a stronger impression when meeting people for the
first time.
I have recently had a baby daughter and have had no problems in
returning to work part time while she is young. She stays at a day care
centre at the university so I am able to visit her during the day to feed her
and give her a cuddle!
In the past women who became scientists and engineers were such a
small minority that they had to fit in with men and do things 'their' way,
but I think that is changing. Now women are much more comfortable
about taking advantage of any different approaches they may have to
solving problems.
22
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Suggested answers
Bending light
1
You should see light on your finger which is in the stream of water.
2
The light is held completely within the stream of water.
3
This question asks you to create your own theory. The scientific
reason is discussed later in this part.
Total internal reflection
C
normal
1a
less dense
medium
for example air
B
more dense
medium
for example glass
1b
less dense
medium
for example air
normal
A
B
C
more dense
medium
for example glass
1c
less dense
medium
for example air
normal
A
B
more dense
medium
for example
glass
A
C
23
2
The beam of light from B to C in the first diagram bends away from
the normal as it moves into a less dense medium.
3
The angle between the line from A to B and the normal is smaller
than the same angles in the other diagrams.
4
The light line from B to C in this diagram is travelling along the
edge of the more dense medium. It does not move into the less
dense medium.
5
The line B to C has a different angle to the normal than the line
A to B in this diagram.
6
The angle between the light line from A to B and the normal is larger
than the same angle in the first diagram.
7
The light line from B to C in this diagram is reflected back into the
more dense medium (glass).
8
The angle between A to B and the normal is greater than the same
angles in the first two diagrams.
9
The angles between A and B and the normal and B and C and the
normal the same in this diagram.
Optical fibres
A
A
A
optic fibre 1
air
optic fibre 2
air
optic fibre 3
(more (less dense) (more (less dense) (more
dense)
dense)
dense)
B
B
C
C
D
B
E
24
C
D
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4
Light travels through optic fibres by total internal reflection.
5
Different angles of light reflect off optical fibre walls.
So what is an optical fibre?
1
A multimode optic fibre has a consistent refractive index inside the
glass core. A graded optic fibre has high refractive index in the
centre with decreasing refractive index material towards the outside
of the fibre.
2
An optic fibre strand is encased in cladding to protect the delicate
glass strand used to transmit light.
3
Graded optical fibres overcome the problems of differing
transmission times.
4
Small diameter core optical fibre is more effective in long distance
telecommunication as it only transmits one impulse at a time,
preventing spreading of the light pulse, therefore allowing it to travel
longer distances without boosting.
buffer jacket
5
silicone
glass core
cladding
optical fibre
polyurethane
strength layer
6
Single optical fibre.
25
26
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Exercise - Part 6
Name: _________________________________
Exercise 6.1
Summarise the properties (characteristics) of optical fibres using
information on pages 10 to 13.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
27
Exercise 6.2
Compare the performance of copper cables and optic fibres in
telecommunications in the following areas.
Copper cables compared to optic fibres
Carrying
capacity
Cost
Rate of
information
transfer
Security
Size
Evaluate the advantages of optic fibres over copper cables.
_________________________________________________________
_________________________________________________________
_________________________________________________________
28
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Exercise 6.3
Multiple choice: circle the letter of the most correct answer
1
Information systems can be classified as:
(A) verbal or non–verbal
(B) short or long distance
(C) electronic or non–electronic
(D) all of the above.
2
Earth
Which property of electromagnetic waves does the diagram show?
(A) Electromagnetic waves can be reflected.
(B) Electromagnetic waves travel at the speed of light.
(C) Electromagnetic waves travel through the ionosphere.
(D) Electromagnetic waves may be amplified.
3
Which communication technology does not use energies from the
electromagnetic spectrum to transfer information long distances?
(A) Television.
(B) Radio.
(C) CD played on a sound system.
(D) Mobile telephone.
4
Identify the above wave.
(A) FM wave
(B) AM wave
(C) Sound wave
(D) None of the above
29
5
Satellites in low Earth orbits are:
(A) mainly used for mobile communications on Earth
(B) travelling faster than satellites in outer orbits
(C) closer to Earth than geostationary satellites
6
The part of the electromagnetic spectrum used for mobile telephone
communication is:
(A) visible light
(B) X–rays
(C) radio waves
(D) microwaves.
7
The type of energy required to run every modern information
transfer technology is:
(A) sound energy
(B) electrical energy
(C) kinetic energy
(D) electromagnetic energy.
8
Which electromagnetic waves are most prone to static interference?
(A) FM waves
(B) AM waves
(C) Microwaves
(D) Light waves.
9
Information sent through long distance telephone lines must be:
(A) coded
(B) digitised
(C) decoded
Short answer questions
10 a) Some information systems have similar patterns of information
transfer. Outline one similarity in the information transfer
patterns of televisions and radios.
__________________________________________________
__________________________________________________
30
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b) Outline one similarity in the information transfer patterns of
computer based communications and land connected telephones.
_________________________________________________
_________________________________________________
11 a) Identify two advantages of using a range of information systems.
_________________________________________________
_________________________________________________
b) Identify one advantage of microwave communication over AM
and FM radio wave communication.
_________________________________________________
_________________________________________________
12 Choose one information system and outline the energy
transformations that occur from the beginning of information
transmission to the end.
_____________________________________________________
_____________________________________________________
13 Explain how a fax machine works.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Long answer questions
14 a) Identify what total internal reflection has to do with optic fibres.
_________________________________________________
_________________________________________________
b) Summarise two properties of optic fibres that make them useful
as communication carriers.
_________________________________________________
_________________________________________________
31
c) Assess why optic fibres are used in preference to copper cables
in telecommunications.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
15 a) Describe the main features of a geostationary satellite.
__________________________________________________
__________________________________________________
b) Explain why a geostationary satellite must be at a height above
the Earth where its revolutionary period is the same as that of
the Earth’s rotation.
__________________________________________________
__________________________________________________
__________________________________________________
c) Justify why a satellite dish on Earth must remain in the same
place and face the same direction once calibrated to a particular
satellite.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
16 a) Explain how information can be transmitted between
information systems that aren’t physically linked.
__________________________________________________
b) Critically evaluate a first hand investigation that you did which
compared communication using AM and FM radio waves. Be
sure to include your results and conclusion.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
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Bibliography
Brain, M. Marshall Brain’s How Stuff Works. How a Cell Phone
Works. <http://www.howstuffworks.com/cell–phone.htm> (accessed 7
September 2000)
Brain, M. Marshall Brain’s How Stuff Works. How Compact Disks
Work. <http://www.howstuffworks.com/cd.htm> (accessed 7 September
2000)
Brain, M. Marshall Brain’s How Stuff Works. How HDTV Works.
<http://www.howstuffworks.com/hdtv.htm> (accessed 7 September
2000)
Brain, M. Marshall Brain’s How Stuff Works. How Tape Recorders
Work. <http://www.howstuffworks.com/cassette.htm> (accessed 26
September 2000)
Brain, M. Marshall Brain’s How Stuff Works. How Telephones Work.
<http://www.howstuffworks.com/telephone.htm> (accessed 7 September
2000)
Brain, M. Marshall Brain’s How Stuff Works. How Television Work.
<http://www.howstuffworks.com/tv.htm> (accessed 7 September 2000)
CyberScience. Fibre Optics in the Kitchen.
<http://www.publish.csiro.au/cyberScience/helix/TH48/TH48B.htm>
(accessed 26 September 2000)
EAN Australia. The system.
<http://www.ean.com.au/syst_numb_ret.htm> (accessed 10 October
2000)
Encarta Encyclopedia. Facsimile transmission.
Schoenherr, S. History of Radio.
<http://history.acusd.edu/gen/recording/television1.html> (accessed 27
September 2000)
33
Schoenherr, S. History of Television.
<http://history.acusd.edu/gen/recording/television1.html> (accessed 27
September 2000)
Selinsky, D. & Brown, G. Marshall Brain’s How Stuff Works. How
Credit Cards Work. <http://www.howstuffworks.com/credit–card2.htm>
(accessed 8 September 2000).
Selinsky, D. & Brown, G. Marshall Brain’s How Stuff Works. How
Credit Cards Work. <http://www.howstuffworks.com/credit–card3.htm>
(accessed 8 September 2000).
Spaargaren, S. Western Australian Women in Science. Sue Spaargaren.
<http://www.swimwithdragons.com.au/cgi–bin/cgiwrap/dragons/allegro.
pl?wis_search.Sue+Spaargaren> (accessed 28 November 2000).
34
Information systems
Student evaluation
Name: ________________________
Location: ______________________
We need your input! Can you please complete this short evaluation to
provide us with information about this module. This information will
help us to improve the design of these materials for future publications.
1
Did you find the information in the module clear and easy to
understand?
_____________________________________________________
2
What did you most like learning about? Why?
_____________________________________________________
_____________________________________________________
3
Which sort of learning activity did you enjoy the most? Why?
_____________________________________________________
_____________________________________________________
4
Did you complete the module within 30 hours? (Please indicate the
approximate length of time spent on the module.)
_____________________________________________________
_____________________________________________________
5
Do you have access to the appropriate resources? eg. a computer,
the internet, scientific equipment, chemicals, people that can provide
information and help with understanding science
_____________________________________________________
_____________________________________________________
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SSCHSC43170 Information Systems
Learning Materials Production
Open Training and Education Network – Distance Education
NSW Department of Education and Training

Information systems - NSW Department of Education

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