INFORMATION SYSTEMS

9.4.1.1 Outline the basic pattern of the information transfer process as – code common to both parties – message – transmission of coded message – decoder

IDEA CODE TRANSMISSION DECODE FEEDBACK Common code:

Pictures, words turn in codes to be a message

Message:

Can be transferred electronically, usually digitally

Transmission:

Carrier wave is decoded, sent to destination Uses either electric current or EM waves

Decoder:

Detects and separates code from the carrier wave Converting the code into the receiver’s code that detects the meaning

9.4.1.2 Identify a range of information systems used daily

Daily Communication systems involve: Telephones Mobile phones TV Radio Internet Email Computers Satellites CD players Fax machines

9.4.1.3 Classify information systems as – verbal and nonverbal – short and long distance – electronic and non-electronic

Definition Examples

Verbal Words, either spoken or text Talking, mobile phone, TV, internet

Nonverbal Pictures, smell, touch, taste Body language, radar, TV, internet

Short distance Presence of the receiver or within immediate area

Talking, body language

Long distance Other states/ countries TV, radar, internet, phone

Electronic Mobile phone, TV

Non-electronic Talking, body language, newspapers

9.4.1.4 Recall phenomena and events where different forms of energy are used

Energy: change to the physical or chemical state of material object occurs

Example:

Electricity is a phenomenon related to the movement of electricity charged particles. Batteries convert chemical (potential) energy to electrical energy.

Types of energy:

Chemical – energy stores in chemicals Potential – energy that can be released later Kinetic – movement energy Heat – energy from differences in temperature Light – energy from light Sound – energy released as noise Electromagnetic – energy carried as waves Electrical – energy carried by electrons Solar – energy from the sun Nuclear – energy released from atoms

9.4.1.5 Identify the transformation of energy at each stage of information transfer in the following devices – land connected telephones, mobiles phones, TV, radios CD players

Device: Info: Transfer:

Land-connected telephones

- Microphone and small loud speaker

Sound Electrical Sound

Mobile phones - Transmitters pick up radio waves

- Microwaves relay message also

Sound Electrical EM waves Electrical Sound

TV - Light is transformed into electrical energy and transmits the TV signal

Light + Sound Electrical EM waves Electrical Kinetic Light + Sound

Radio - Microphone converts sound into electrical energy

Sound Electrical Radio waves Electrical Sound

CD players - Stores information digitally

- Laser light to read code (light = decoder)

Laser light electrical EM waves Sound

9.4.1.6 Discuss The advantages of using a range of information systems

Transferred at the speed of light Wide range of audience Received immediately Communication can be without travel, saving money and time Greater mobility and compact Warning system Cheaper and high quality Confidential Advertising to target audiences If one fails others are available

9.4.2.1 Identify the types of waves in the EM spectrum currently used for communication systems as – visible light – infra-red – microwaves – radio waves (TV, AM, FM)

EM refers to waves of energy which are caused by the varying motions of charged particles.

EM waves do NOT need a medium such as air through which to travel. Parts of the EM spectrum used for communication – visible light, infrared, microwaves,

radio waves (AM & FM)

Uses for EM waves in communication Basic facts

Radio waves – radio, TV Microwaves – mobile phones, Wi-Fi Infra-red – remote controls for TV,

stereos, cordless computer devices Visible light – optical fibres, telephone

Radio waves have the lowest energy. All EM waves travel at the speed of light. As wavelength decreases, frequency

increases.UHF: ultra-high frequency and VHF: very high frequency

9.4.2.2 Compare the advantages and disadvantages of using microwaves and radio waves in communication technologies

RADIOWAVES:

Advantages Disadvantages

Can be transmitted in space longer distances

Do NOT require line-of-sight transmission

Reflects off objects on Earth can reach remote places

Can travel further at night

Can be absorbed by water, oxygen, carbon dioxide in atmosphere

Affected by static, over power lines and lighting

Require more electrical power for transmission that microwaves

Heavy rainfall absorbs Same signal can arrive at different time

“ghost effect”

MICROWAVES:

Advantages Disadvantages

Different bandwidth to radio waves no crowding

Do not spread out very much minimal energy is wasted

Possible to send more than one signal out at once

High frequency more information transmitted

Can be reflected Requires less electricity

Travel in straight lines require line-of-sight

May be blocked by hills, buildings, mountains

Water molecules tend to absorb them Signals must be relatively strong for

information to transfer

9.4.2.3 Identify communication technologies that use energies from the EM spectrum for communication purposes

Energy Description Communication Technology

Visible light Replacing copper lines and phone lines

Last much longer

Optical fibers

Infra-red TV, video, garage doors Remote control communication

Microwaves Used for satellite phones in isolated areas Satellite technologies

and for mobile phone conversations

Radiowaves and microwaves

Communication between individual mobile phones

Mobile phone networks

Shortwave radio Very high frequency (VHF) and ultrahigh (UHF)

TV broadcasting

Shortwave and longwave radio

Used for broad range of technologies including AM and FM broadcasting

Radio broadcasting

9.4.3.1 Identify that where information systems cannot be physically linked the information may be transmitted in wave form through the atmosphere or space

The first type of long distance without wires used RADIO WAVES, which can travel in a direct straight line, can be bounced off the upper layers of the earth’s atmosphere.

Transmitting antenna produces waves that travel through air or space at great speed and over a range of distances

Receiving antenna tuned to particular frequencies will detect the signal and relay this to the receiving communication device

Places where communication by physical links (e.g. wires) is NOT practical or possible include –space, airplanes, ships

Locations where rapid and/or long distance communication was made possible by radio include – ship-to-ship, airplane pilots, international communication

9.4.3.2 Identify the properties of energy from the EM spectrum that make it useful in communication technologies including – speed of travel – ability to travel in a straight line – ability to be reflected

Speed of Travel:

- 300 000 km/s - Time between sending, receiving and decoding is almost instantaneous

Ability to Travel in a straight line:

- Straight lines make their path predictable - Always will travel in a straight line unless a change in medium they travelling through

Ability to be reflected:

- Reflection is the change in direction of a wave o Due to it bouncing off a boundary between two media

- AM waves bounce off the ionosphere

9.4.3.3 Describe the individual properties of visible light, radio waves (AM, FM, TV) and microwaves and relate these to their use in communication

VISIBLE LIGHT:

Light (having most high frequency) has huge information carrying capacity Light can be refracted and reflected to achieve total internal reflection. Optical fibres are used to transmit light pulses generated by an electrical. The use of the fibre

ensures privacy and an energy efficient way of sending information.

e.g. bar codes, fax, optic fibres

Visible light diagram:

MICROWAVES:

Microwaves travel in straight lines line-of-sight High frequency large carrying capacity Easily absorbed and scattered in the atmosphere – they need directional aerials for transmission

and reception (to ensure sufficient signal strength) Can easily pass through rain, smoke, fog and they also pass through the ionosphere and space

e.g. mobile phones, TV, satellite communication

RADIO WAVES – AM:

AM radio waves reflecting off layers of the atmosphere i.e. ionosphere and are rounded “radical waves” which allows them to be transmitted out-of-sight. This gives AM radio very long range.

Relatively low frequency carry small amounts of information

Can travel through almost any medium e.g. underwater, buildings, mines

RADIO WAVES – FM:

Much higher frequency than AM radio waves carry more information Shorter wavelength do not diffract well around large objects FM radio waves spread out from a point source for broadcasting Do NOT reflect of the ionosphere must be line-of-sight

RADIO WAVES – TV:

Use VHF and UHF waves (very high, ultra-high) Both VHF and UHF waves spread out from point source i.e. the aerial for broadcasting Travel at speed of light fast communication Weak signals can occur as buildings & hills absorb waves UHF travel in straight lines useful for crowded urban areas (good reflection)

VHF used for FM radio, TV, marine radioUHF used for TV, police radio

9.4.4.1 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

Geostationary satellite: orbits the Earth once every 24 hours

o Remains at the same point in the Earth at all times

Same spoto For reception it stays at the same

point and the satellite dish must face the same direction

To ensure signals are received and retransmitted

o Microwaves are used because they can travel through the ionosphere and can diffract

o The area of the word covered by the satellite is its footprint

Comparing geostationary and low-earth orbit satellites:

Geostationary satellites Low-earth orbit satellite

High altitude – 36 000km above equator

Low altitude – 500 to 1500km Covers other 20% of earth Many low earth satellites must be used – approx.

Covers 80% of earth These satellites remain above the

same point on the equator at ALL times

Good for communications or weather forecasting satellites

3 geostationary satellites exist

15 Commonly used for high resolution land imagery

and mobile telecommunications e.g. mobiles, ships, airplanes

Because these satellites are so close to earth, there is no time delay in information transmission

9.4.4.2 Explain why Earth-based satellite dishes must always face the geostationary satellite communicating with it

A satellite dish must face the same direction and must remain at the same location with respect to the surface of the earth.

This is because the satellite dish is aimed a particular satellite.

The satellite the dish is in contact with is always in the same relative position in sky.

The parabolic shape of the dish focuses the signals into the central point.

9.4.5.1 Identify communication technologies that transform one type of energy into electrical energy

Communication technology Type of energy transformed into electrical energy

Microphone Sound

Radio Sound

TV camera Light

Scanner Light

Keyboard Kinetic

Receiving antenna EM radiation in radio frequency

9.4.5.2 Describe the transmission of images using digital information in terms of scanning of the input image along very thin lines

The chip is divided up into millions of tiny squares called pixels.

Laser light ‘scans’ image in very thin lines image is stored in analogue form charge-coupled device converts it to a digital signal (BINARY CODE) transmitted using telephone cables (fax machine) receiver converts digital signal back to analogue image is received!

Fax machine forms of energy:

Light energy electrical energy binary code sensor voltage

9.4.5.3 Explain how the coding of the image into a series of zeros and ones allow its transmission and ultimate decoding

Digitalising an image i.e. dividing it into a grid of dots Each dot is represented by a BIT that has a value of either 0 or 1. Images and data are converted to a series of 1’s and 0’s (digitalised) to be transmitted

on the RECEIVING end, a device reads the incoming data (as a binary code), translates the 0’s and 1’s, back into dots (the image)

Binary digits can be represented and/or transmitted as voltages or as pulses or light ∴ WIRE OR OPTICAL FIBRE

The coding of a signal into a series of 0’s and 1’s allows its transmission and ultimate decoding because an accurate record of the original signal can be made using digits (0, 1)

9.4.6.1 Outline properties of optical fibers as communication carriers

An optic fibre consists of 2 sections with a covering;o Glass core – runs through the centre of the strando Glass cladding – surrounds the core

Properties of optical fibres as communication carriers;

The main job of an optical fibre is to guide light with minimum loss of signal

The glass in the cladding is optically less dense than the core glass. As such, the cladding glass has a lower refractive index. This causes the cladding to act as a mirror for light travelling in the core. As a result, the light (infrared) travels through the core by a series of continuous reflections TOTAL INTERNAL REFLECTION.

Made from very pure, almost mineral-free glass allows for long distance transmission of light Cable is flexible and can be easily bent can be bent

around obstacles without need for relay (reflection) devices Total internal reflection light is transmitted with very

little loss of energy over long distances Travels at 2/3 speed of light in a vacuum makes

communication using optic fibre VERY fast Attenuation is the loss of signal strength—there must be

some loss of signal strength in an optical fibre

Two types of optical fibres

Single-mode fibre Multi-mode fibre

Extremely thin cores Designed to force the light to travel in a

single mode They accept light only along the axis of

the fibres need laser light

Larger cores than single-mode fibres They accept light from a variety of

angles Loses more signal

∴ An optical fibre cable is a technology that uses glass (or plastic) threads (fibres) to transmit data via light. They are a network of glass cables insulated cladding.

9.4.6.2 Outline the principle of total internal reflection and relate this to the advantages over more conventional carriers of information

When light is passed from one substance to another, its path is refracted (bent). The amount of light is bent between 2 materials is measure by the refractive index.

o Glass (dense) higher refractive indexo Air lower refractive indexo And therefore, light travels faster through AIR than through GLASS!

Total internal reflection occurs when light travels from a more-dense to a less-dense medium (e.g. glass to air)

The greater the angle of incidence (starting angle of light), the greater the critical angle (end result)

TOTAL INTERNAL REFLECTION

Total internal reflection ONLY occurs when…

1. The rays of light must travel from a dense medium to a less dense medium.

2. The angle of incidence must be greater than the critical angle.

9.4.6.3 + 9.4.6.5 Outline the differences and relative merits in the use of fibre optic cables and metal cables to transmit and receive information

Advantages of optic fibre over copper wires: Greater bandwidth carry more data Not affected by radio waves – no static Thinner and lighter Less susceptible to corrosion longer lifespan Can carry digital and analogue information More secure Can stretch further and overall cost cheaper

Disadvantages of optic fibre over copper wires:o Very expensive to installo More fragile than wire o Repeaters need to be added to boost signal strengtho Optic fibres require coatings

Type of cable

Carrying capacity Cost per km Rate of information transfer

Security

Optic fibre Large carrying capacity (several GB of data per second)

Very expensive (but prices are dropping)

10 GB/s High security as it optic fibre is harder to tap into and be intercepted

Copper wire

Small carrying capacity

Cheap because new technology is being introduce

2MB/s Low security as EM radiation is emitted from copper cables this can be detected and decoded