Information systems - NSW Department of Education
Transcription
Information systems - NSW Department of Education
Gill Sans Bold Senior Science HSC Course Stage 6 Information systems 0 20 I SSCHSC43170 2 er b to T S c O EN g in D M t a r EN o p or AM c n 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 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you on behalf of the 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 electromagnetic waves 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 vii viii 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 Gill Sans Bold Senior Science HSC Course Stage 6 Information systems Part 1: Get the message? 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 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 Gill Sans Bold 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 Part 1: Get the message? 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 – land connected telephones – mobile phones – television – radios – Compact Disc players discuss the advantages of using a range of information systems. Information systems Gill Sans Bold 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: – land connected telephones – 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 Part 1: Get the message? 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 Gill Sans Bold 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. Part 1: Get the message? 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 Gill Sans Bold 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. Part 1: Get the message? 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 Gill Sans Bold 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. Part 1: Get the message? 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 Gill Sans Bold 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. Compact Disc players 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 Part 1: Get the message? 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 i 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 Gill Sans Bold 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. Part 1: Get the message? 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 Gill Sans Bold 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. Part 1: Get the message? 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 Gill Sans Bold • 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. Part 1: Get the message? 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 Gill Sans Bold 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. Part 1: Get the message? 19 Summary Write your own summaries next to each of the following information systems. Information system 20 Summary Information systems Gill Sans Bold 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 _____________________________________________________ _____________________________________________________ Part 1: Get the message? 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 Gill Sans Bold Appendix Part 1: Get the message? 23 24 Information systems Gill Sans Bold 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 Part 1: Get the message? 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 Gill Sans Bold 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. Compact Disc players 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) Part 1: Get the message? 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 Gill Sans Bold 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 Part 1: Get the message? 29 30 Information systems Gill Sans Bold 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 Part 1: Get the message? 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 Gill Sans Bold 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 Part 1: Get the message? 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 Gill Sans Bold 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 o nc 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 Gill Sans Bold 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 Suggested answers................................................................. 25 Exercises–Part 2 ..................................................................... 27 Part 2: Waves waves waves 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. 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 2 Information systems Gill Sans Bold 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 Part 2: Waves waves waves 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 Gill Sans Bold 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. Part 2: Waves waves waves 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? _____________________________________________________ Check your answers before moving on. 6 Information systems Gill Sans Bold 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. Part 2: Waves waves 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 Gill Sans Bold 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. Part 2: Waves waves waves 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 Gill Sans Bold 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. Part 2: Waves waves waves 11 Information systems ctr o m a g n eti c sp e ctr One ele u he hundred infrared m waves can fit into a millimetre. You are familiar 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 read this! t p on a nd le a v e it bl an kt o re p s re ow av es o n t h e e l e ct r o m ag ne en ite light. re t wh r it e le v is i o n w a v e s le . L w on th um di o ct r The radio waves your television receives are about one metre in length. et nd at L o c ate r a e oc 0a M M ic ce icr ro n o ph wa tim wa v o e e r ves n t m es b ove e in ar e ic n r owoth s a len on av pro nd gth e . e s. duc mo e bil e p g e. ru m o n pag e 1 ur ran e ct 1 0 a nd c olo u m age t ru ve e ha e hs on se gt d to u n un t in yo le ro fi s ve a n ve wa ally ca e wa ent ner ves etr he r e a im l t ffe r g w ill Al di ve nd m a a we us ho tho 1 0 a nd c ol o ur i tp it o m a g n e ti c s p e e a L o ca L a oc te x- ra c a m m a ra ys o et i te g t h e e le c t r o m a g n . w on T tu he ne r s ad i i to nto o w 1 ar av km e es in aro yo le un ur ng d ra th 10 di ! 0 o m s ve co ctr o th o n p ag e 1 0 and e le on um sp ge ru m g n e t ic s p e c t om a ctr ele a v i ol et r a y s c tr tic pe ic s o m a gn e t e le ct r the on s pa ul tr ur te lo a oc pe it y e n d c ol o u r th e 10 a ys on el e c t r o m a g n e ti cs he pa nt ge o ll o r e e n. a rk g it d ur lo dc ay 10 00 wavelengths of ultraviolet (UV) light can fit into one millimetre. This electromagnetic wave is responsible for sunburn. re an n tr . en it g p a ge 1 0 c on n f r a -r e d w av e s te i ca Lo r ic em Lo c at d. L o ca t e l i g h e. it blu L ur Size matters! 1 0 an d co l ou r m on y a re ra o a ht x- int ves rig on fit a ss illi s w a y. m gth ese y p bod ne n h he r O ele . T t t ou av re a y w et ll th gh m a u illi m ro m o s th s ge t ru o 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 co on pa s c pe Gamma rays with 0.01 nm wavelengths can fit 100 million wavelengths into a millimetre. Imagine that! These waves are so small that they can affect the genes inside cells. This is why gamma rays are so dangerous. e tr lec om a g n e t i c s p e ct r u m on 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. Part 2: Waves waves waves 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 Information systems Gill Sans Bold 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. Part 2: Waves waves waves 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 Information systems Gill Sans Bold 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. Part 2: Waves waves 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 Information systems Gill Sans Bold 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. Part 2: Waves waves waves 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. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 20 Information systems Gill Sans Bold 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. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 Write one long answer question with its answer based on the information in this part. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 2: Waves waves waves 21 ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 22 Information systems Gill Sans Bold 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 Part 2: Waves waves waves 23 24 Information systems Gill Sans Bold 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. Part 2: Waves waves waves 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 Information systems Gill Sans Bold Exercises - Part 2 Exercises 2.1 to 2.3 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 Part 2: Waves waves waves 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. Information systems Gill Sans Bold 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 Part 2: Waves waves waves 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 Information systems Gill Sans Bold Senior Science HSC Course Stage 6 Information systems 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 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 Gill Sans Bold 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 Suggested answers................................................................. 13 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. 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 2 Information systems Gill Sans Bold 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 Information systems Gill Sans Bold 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 Information systems Gill Sans Bold 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. Information systems Gill Sans Bold 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 Information systems Gill Sans Bold 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 Information systems Gill Sans Bold 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. Information systems Gill Sans Bold 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 Information systems Gill Sans Bold Exercises - Part 3 Exercises 3.1 to 3.3 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 Information systems Gill Sans Bold 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. Information systems Gill Sans Bold 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. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ 22 Information systems Gill Sans Bold 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 Gill Sans Bold Senior Science HSC Course Stage 6 Information systems Part 4: Messages from space 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 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 Gill Sans Bold 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 Suggested answers................................................................. 19 Exercises–Part 4 ..................................................................... 23 Part 4: Messages from space 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. In this part you will be given opportunities to learn to: • 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. 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 2 Information systems Gill Sans Bold 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? _____________________________________________________ _____________________________________________________ Part 4: Messages from space 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. 4 Information systems Gill Sans Bold 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. _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 4: Messages from space 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. 6 Information systems Gill Sans Bold 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°). Part 4: Messages from space 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. 8 Information systems Gill Sans Bold 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. Part 4: Messages from space 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 Information systems Gill Sans Bold 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. Part 4: Messages from space 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. 12 Information systems Gill Sans Bold 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. Part 4: Messages from space 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. 14 Information systems Gill Sans Bold 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 G T C T U I O S D E F W A N J K L S R R J O Q E L E C T R O M A G N E T I C W A V E F H T C O N S T E L L A T I O N T U G A W C B M E W C S B N J K O R R U Y K L F R H N E B M L S T H T R A N S M I T T I N G A E R I A L E R D A E A A A H Y K J C Z T Y V Z W V A O C F G G S W T E L E V I S I O N I R M I D W O H S E G A E I H T K A Q F B M T H U N F E M G A Y Y R E D O W N L I N K O Y U R G U A M N T K I I U A H N A H C C B I T I D A I R U I E L L I P T I C A L O R B I T J S E L T N O L L O K L I S T A R T O O I L L H R L H I G L O R L I T M N H T Y E Y O K S E I Y O C A I I X P N E I N T E N S I T Y A F A R R A D T U N P K L A F L J J M A T O T F L A B T W E N T Y F O U R H O U R T P B K H N I S I G D T I R O S B J L T T U O O E H L N O T O H I D K V L S S O L A R P A N E L S K R M N I S H L N V A W D G J Y E D H K L L L B N S P H V F R E Q U E N C Y C C E R E T I I B H L G A F M B H I G H E A R T H O R B I T D C R I G H T N G L E D G H F R P O F V R E A Check your answers. Part 4: Messages from space 15 16 Information systems Gill Sans Bold Appendix Part 4: Messages from space 17 18 Information systems Gill Sans Bold 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). Part 4: Messages from space 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) 20 Information systems Gill Sans Bold Satellites receiving aerial solar panels electrical circuitry transmitting aerial Summary R T E L E C T R O M A G N E T C O N S T E L L T I O N A I C E L T R A N S M I T T I N G T E L E V I S I O N E C W A V E G C R E A E R I A L V V O I I W T N E Y G A A R E T O S M A M T U E N L L R H I L I I O C I N A R L B A T T W E I D O I N S S H R I D O W N L I N K U L L I P T I C A L O R B I N T E N S I U R H O U R S I T T Y K N T Y F O I O S O L A R P A N E L S T R B G F R E H T A Part 4: Messages from space Q U E N C Y H I G H E A N G L E I R T H O R B I T 21 22 Information systems Gill Sans Bold Exercises - Part 4 Exercises 4.1 to 4.4 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. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 4: Messages from space 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 Part 4: Messages from space 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 Gill Sans Bold 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 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 Gill Sans Bold Contents Introduction ............................................................................... 2 Coding and decoding information.............................................. 3 Energy transformations ............................................................. 7 Electrical impulses..................................................................... 8 Generating electrical impulses ............................................................9 Summary................................................................................. 12 Suggested answers................................................................. 15 Exercises–Part 5 ..................................................................... 19 Part 5: Information through impulse 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. In this part you will be given opportunities to learn to: • 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. 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 2 Information systems Gill Sans Bold 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 Part 5: Information through impulse 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 Gill Sans Bold 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 Part 5: Information through impulse 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 Gill Sans Bold 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 electromagnetic waves 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 Check your answers before moving on. Turn to Exercise 5.1 at the back of this part to identify communication technologies that transform different energies into electrical energy. Part 5: Information through impulse 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 Gill Sans Bold 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. Part 5: Information through impulse 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. Part 5: Information through impulse 11 Summary 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 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 Gill Sans Bold 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 Part 5: Information through impulse 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 Part 5: Information through impulse 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 electromagnetic waves 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) Part 5: Information through impulse microammeter (multimeter) 17 18 Information systems Gill Sans Bold Exercises - Part 5 Exercises 5.1 to 5.2 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 Part 5: Information through impulse 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 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 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 Suggested answers................................................................. 23 Exercises–Part 6 ..................................................................... 27 Bibliography ............................................................................ 33 Part 6: Fibre optics 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. In this part you will be given opportunities to learn to: • 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. 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 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. Part 6: Fibre optics 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 Part 6: Fibre optics . 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. Part 6: Fibre optics 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 Gill Sans Bold 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. 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. Part 6: Fibre optics 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 Information systems Gill Sans Bold 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. Part 6: Fibre optics 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 Information systems Gill Sans Bold 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. Part 6: Fibre optics 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 Information systems Gill Sans Bold 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. Part 6: Fibre optics 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. 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. 16 Information systems Gill Sans Bold 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. Part 6: Fibre optics 17 18 Information systems Gill Sans Bold 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'). Part 6: Fibre optics 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 Information systems Gill Sans Bold 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. Part 6: Fibre optics 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 Information systems Gill Sans Bold 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 Part 6: Fibre optics 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 Information systems Gill Sans Bold 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. Part 6: Fibre optics 25 26 Information systems Gill Sans Bold Exercise - Part 6 Exercises 6.1 to 6.3 Name: _________________________________ Exercise 6.1 Summarise the properties (characteristics) of optical fibres using information on pages 10 to 13. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 6: Fibre optics 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 Information systems Gill Sans Bold 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 Part 6: Fibre optics 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 (D) all of the above. 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 (D) all of the above. 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 Information systems Gill Sans Bold 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. _________________________________________________ _________________________________________________ Part 6: Fibre optics 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. __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ 32 Information systems Gill Sans Bold 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) Part 6: Fibre optics 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 _____________________________________________________ _____________________________________________________ Please return this information to your teacher, who will pass it along to the materials developers at OTEN–DE. SSCHSC43170 Information Systems Learning Materials Production Open Training and Education Network – Distance Education NSW Department of Education and Training