The World Communicates

Contextual Outline

Humans are social animals and have successfully communicated through the spoken word, and then, as the use of written codes developed, through increasingly sophisticated graphic symbols. The use of a hard copy medium to transfer information in coded form meant that communication was able to cross greater distances with improved accuracy of information transfer. A messenger was required to carry the information in hard copy form and this carrier could have been a vehicle or person. There was, however, still a time limit and several days were needed to get hard copy information from one side of the world to the other.

The discovery of electricity and then the electromagnetic spectrum has led to the rapid increase in the number of communication devices throughout the twentieth century. The carrier of the information is no longer a vehicle or person — rather, an increasing range of energy waves is used to transfer the message.

The delay in relaying signals around the world is determined only by the speed of the wave, and the speed and efficiency of the coding and decoding devices at the departure and arrival points of the message. The time between sending and receiving messages through telecommunications networks is measured in fractions of a second allowing almost instantaneous delivery of messages, in spoken and coded forms, around the world.

This module increases students’ understanding of the nature, practice, application and uses of physics and current issues, research and developments in physics.

The wave model can be used to explain how current technologies transfer information

1.1 - Describe the energy transformations required in one of the following: mobile telephone

Types of energy include: Heat Light Sound Electrical Magnetic

Sound energyElectrical energyradio energyelectrical energysound energy

The microphone built into mobile phones change sound energy (kinetic energy of vibrating particles in air) into electrical energy. This is then converted by the phone into electromagnetic energy in the form of radio signals that the phone transmits to a receiving base station. The energy changes occurring at the base station depends on whether the mobile phone call is to:

Close fixed station- the base converts the radio waves back into electrical that goes through a copper wire to a switching station close to destination and then to the fixed phone as electrical through copper to receiving telephone then converts it to sound energy

Another mobile- The base converts the electromagnetic signal into electrical and then transmit them to a switching station close to receiving station. Then as electrical switches to the nearest base station then to the mobile then in radio waves the receiving mobile changes radio to electrical then to sound from the speakers

Distant fixed phone – the base station transmits either as electrical or light energy via optical cables to a switching station close to its destination. Then from the switching station travelling via copper wires network as electrical converts into electrical energy which is changed back into sound energy by the receiving phone.

1.2 - Describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

Depending upon the type of wave and the medium in which they are traveling, waves may be traveling in one, two or three dimensions

The source of all waves is a vibration or disturbance. The energy provided from the vibration passing from the place of origin to a place

further away is the wave. Therefore a wave is a transfer of energy from a place of origin to a point further

away.o One dimensional waves: Waves that can only travel in one direction from

one point to another in an object. Demonstrated by using a slinky to create the motion of a transverse and longitudinal wave. Wave can only travel in one direction.

o Two dimensional waves: A wave travelling outwards from where a stone

has dropped into water is travelling in two dimensions. Travelling from a point source of disturbance in still water. (Circular wave front)

o Three dimensional waves: A point source of sound results in a sound wave that immediately travels from the source in three dimensions with a spherical wave front.

1.3 - Identify that mechanical waves require a medium for propagation while electromagnetic waves do not

The source of all waves is vibration/energy. This transfer of energy by waves can be demonstrated when: a surfer bobs up and down in the swell

Waves(a travelling disturbance which transfers energy but doesn’t transport matter)

Mechanical waves, such as sound waves, water waves and earthquake waves need a medium (a substance) to travel through, they cannot move from one point to another if there is nothing (a vacuum) between the two points.

There are two types:Transverse - In a transverse wave, the particles of the medium vibrate in a plane that is perpendicular to the direction of propagation of the wave.Longitudinal - In a longitudinal wave, the particles of the medium vibrate in the same direction as the direction of propagation of the wave.

Electromagnetic waves do not need a medium to travel through. An example of this is in space, which is a vacuum, if you call out in space your sound waves do not penetrate out of your space suit. However electromagnetic waves do, therefore you can see the light from the sun.

EM waves travel at 300 million m/s(speed of light). They transfer energy in waves that consist of electric and magnetic fields at right angles to each other Em waves include:UV raysLight wavesInfrared raysRadio wavesMicrowavesTV rays Useful for communicating over long distances then matter waves. This is because it travels fast and can travel through space very conveniently. E.g. A GPS system. It needs to send rays to a satellite and then receive info from rays.

In addition to these advantages Em waves unlike matter waves don’t lose energy through friction from oscillating

1.4 - Define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction, crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

Wave model- best model available to explain the behavior of different types of energy

Rarefaction: Areas of low and minimum pressure in longitudinal waves

Compression: Areas of high and maximum pressure in longitudinal waves

Crest: The highest points of waves (i.e. The maximum positive displacement)

Trough: The lowest points of waves (i.e. The maximum negative displacement)

Medium: the material in which the wave is propagating.

Displacement: distance traveled by one particle in a wave from its resting position

Amplitude: The maximum size of particle displacement from the undisturbed state

Period: the time it takes for a single wave to pass a fixed point. T and f are related through a reciprocal relationship, i.e. T =1/ f

Frequency: the number of waves that pass a fixed place per second. Measured in cycles per second (Hz) - 1Hz is one cycle or wavelength passing a point per second.

Wavelength: The distance between two adjacent crests and troughs. It includes and entire crest and an entire trough

Velocity: speed at which a wave propagates. It is how fast the wave transfers energy away from a source v= f l

Wave front: Either the crest or trough of the wave which is perpendicular to the direction

In Phase: Two points on a wave are in phase if, at a particular instant, they have the

same displacement and the same velocity

Features of a wave model can be used to account for the properties of sound

2.1 - identify that sound waves are vibrations or oscillations of particles in a medium

As an object vibrates it sets up a series of compressions and rarefactions that move through a medium and are detected by our ears. All sound waves are vibrations in a medium that result in pressure variations within that medium.

2.2 - relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them

Compressions are areas of high pressure and therefore when a longitudinal wave such as a sound wave is represented as a transverse wave these areas of high pressure are equivalent to crests. Rarefactions however represent areas of low pressure and therefore are equivalent to a trough.

2.3 - explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

The higher the pitch the higher the frequency, and the lower the pitch the lower the frequency. The louder the sound the bigger the amplitude, a soft or low volume sound is said to have smaller amplitude

2.4 - explain an echo as a reflection of a sound wave

An echo forms when a sound wave reflects off a hard surface and rebounds back to its original source

If you are further away from the surface of reflection you are likely of hearing more of the sound, compared to when you are closer to the surface.

They are used in sonar and radar detection of animals or other objects in the water. Bats use radars echoes to dodge obstructions when flying.

2.5 - Describe the principle of superposition and compare the resulting waves to the original waves in sound

The principle of superposition states: If two or more waves of the same type pass through the same medium at the same time, the displacement of any point is the sum of the individual displacements of each wave.

Interference: When waves meet they interact as they pass through each other, reinforcing or cancelling at different points. Possible to produce no sound from two sound waves, the crest of one wave is precisely equal to the amplitude of the trough of another wave, but the second wave is out of phase by 180 degrees from the first, complete loss of amplitude can occur resulting in no sound (destructive interference). In the same way if the crest of another wave coincides with the crest of another wave, the amplitude will be doubled hence a louder sound produced (constructive interference).

Recent technological developments have allowed greater use of electromagnetic spectrum

3.1:Describe electromagnetic waves in terms of their speed in space and lack of requirement of a medium for propagation

Electromagnetic waves are produced by accelerating charges. As electrons are accelerated in aerials or within atoms they generate changing electric fields, this in turn produces changing magnetic fields, resulting in another electric field. Hence EM waves propagate through no medium. As an EM wave passes a point no individual particle moves. Since EM waves aren’t subject to the same energy loss as mechanical waves, through inelastic collisions and friction all EM waves travel at 3x108 ms-1 in a vacuum (space), however slightly slower in denser medium such as glass, plastic, atmosphere due to refraction.

3.2:Identify the electromagnetic wavebands filtered out by the atmosphere, especially UV, X-Rays and Gamma Rays

Earth’s ionosphere and atmosphere filters out most of the electromagnetic waves except for visible light and radio waves. UV, X-rays and gamma rays are filtered out, these are harmful to humans. Waves which have a smaller wavelength yet a greater frequency than visible light are generally filtered out by the atmosphere. However some types of UV radiation still penetrate the atmosphere.

3.3:Identify methods for detection of various wavebands in the electromagnetic spectrum

3.4:Explain that the relationship between the intensity of electromagnetic radiation and distance from a source is an example of the inverse square law:

The inverse square law:

The inverse square law states that the intensity of electromagnetic radiation is inversely proportional to the square of the distance from the source of the radiation. When the distance is doubled, the intensity decreases to one forth the original value and so on.

Consider light waves emanating from a point source of light in the form of spherical waves (three dimensions). The energy of the light spreads out as the distance from the source increases. Intensity is a measure of the energy per unit. Intensity is inversely proportional to the square of the radius.

3.5: Outline how the modulation of amplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit information

A wave carry energy is not carry info so we need to have it modulated refers to the adding of information to a carrier wave either by superimposing signals of varying frequency or amplitude. You either to one or the other to add info.

1. AM (amplitude modulation) can be used to transmit information by superimposing a signal wave with a carrier wave to alter the amplitude of the superimposed wave, but not the frequency.

AM is used to:o Am radio broadcastingo The variation in the amplitude of a wave is decoded by a radio receiver to

produce the signal which is amplified by internal circuitry to be converted.o Modulating Visible light, which can be used to send and receive sound

waves with devices such ADV: requires a smaller bandwidth of frequencies for transmission possible.

The number of transmitters in an area is larger DIS: Prone to interference

2. FM (frequency modulation) is used to transmit information by superimposing a signal wave with a FM modulating carrier wave to alter the frequency of the superimposed wave.

FM is used to:o Broadcast on FM radioo Modulate microwaves to transmit mobile phone signals.

ADV: less interrupted by interference. Also better for music DIS: Because of different transmitters must be allocated different frequencies.

Therefore there is limited number of transmitters in a given area. High demand for competition

3.6 - discuss problems produced by the limited range of the electromagnetic spectrum available for communication purposes

a) Distance- attenuation is when waves decrease in strength after travelling over long distances (inverse square law). This affects communication because the signal could become much more weak and be less affective for the receiver.

- To reduce this, e-m waves need to be sent out with great strength initially or be amplified at booster or repeater stations as they travel.

-b) Congestion of Frequencies: As more and more people access the limited range of

frequencies, they become more and more congested and interference may occur.- To reduce this, new method of technology need to be created which utilize

other type of e-m spectrum. Also, there is no interference when infra red and light waves are used as forms of communication because they are utilized within enclosed systems where penetration and attenuation are problems

-c) Health Aspects: Microwaves used in mobile phones in particular are controversial

as little is known if their frequency is high enough that they are able to alter human cells.

d) Summary: Congestion of frequencies, selling off rights to previously restricted parts of the electromagnetic spectrum, possible health risks, interference, not secure and affected by weather conditions (scatted by water droplets, affected by changes in the ionosphere).

4. Many communication technologies use applications of reflection and refraction of electromagnetic waves

4.1 - describe and apply the law of reflection and explain the effect of reflection from a plane surface on waves

The law of reflection states that the angle of the incoming or incident wave in relation to a line perpendicular to the reflecting surface (normal) at the point where the incident wave hits the surface is equal to the angle the reflected wave will make with the normal.

The angle of reflection equals the angle of incidence The incident ray the reflected ray and the normal all lie in the same plane All surfaces obey the law of reflection Electromagnetic waves can be reflected from smooth or irregular surfaces.

They both obey the law of reflection. When light is reflected of an irregular surface the incident rays are parallel, but are reflected at various angles based on the surface.

4.2 - describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer

Visible light: Rays of light from a distant object will be brought to a focus by a concave mirror. Both optical and radio telescopes use this principle to collect faint electromagnetic waves from distant celestial objects. Convex mirrors used on cars allow drives to see ‘blind corners’. Car headlights in the shape of a parabolic mirror place a light bulb (the source) at the focus which in turn reflects these light rays in a set of parallel rays.

Radio waves: Can be reflected off the ionosphere (a layer of ionised air) and as a result can be bounced around the curvature of the earth, overcoming the problem of ‘line of sight’ communication.

Microwaves: Are not reflected from the ionosphere and hence have to be boosted at regular intervals to prevent information loss.

4.3 - describe one application of reflection for each of the following: plane surfaces, concave surfaces, convex surfaces and radio waves being reflected of the ionosphere.

Plane surfaces Periscopes, cosmetic mirrors Concave surfaces Used in satellite dishes which are used to boost the intensity of the signal to

another station. Also used in torched and headlights

Convex surfaces In driving mirrors a convex mirror gives a wider field of view than a plane mirror of the same size. Convex mirrors are also used at blind corners to allow a driver to see any oncoming traffic before the turn is made.

Radio waves being reflected by the ionosphere

Can be reflected off the ionosphere (a layer of ionized air) and as a result could be bounced around the curvature of the earth, overcoming the problem of ‘line of sight’ communication. This is because it has ionized air particles of electrons and ions

4.4 - Explain that refraction is related to the velocities of a wave in different media and outline how this may result in the bending of a wave front.

Refraction is the phenomenon where waves that are incident on any angle except the normal bend as they pass from one medium to another. For example, in light the direction can change abruptly, similarly when light leaves a denser medium it speeds back up and the direction of the light changes again This changing of direction when light moves from one material to another is called refraction. The medium has to be transparent. If a wave is entering into a denser medium, the velocity will slow down and hence cause the wave to bend towards the normal, however if the wave is entering a less dense medium it will bend away from the normal.

4.5 - define refractive index in terms of changes in the velocity of a wave in passing from one medium to another

The refractive index (or index of refraction) of a medium is a measure of how much the velocity of a wave is reduced inside a medium.The refractive index is equal to the ratio of the wave speeds in the two media. Refractive index is a comparative measure of the velocities of EM radiation in a vacuum and in the material.

4.6 - define Snell’s Law:

The law says that the ratio of the sines of the angles of incidence and of refraction is a constant that depends on the media. Snell’s law is a ratio of the wave speeds in two media.

4.7 - identify the conditions necessary for total internal reflection with reference to the critical angle

The critical angle is the angle where total internal reflection prevents the ray from escaping from a denser medium to a less dense medium. The angle of incidence where the ray is trapped in the higher refractive index material is the critical angle. The conditions for total internal reflection are:

- The angle of incidence to reach the critical angle, and hence be exceeded causing the refracted ray to remain trapped within the transparent medium

- The wave has to be entering a medium with a lower refractive index in order for the refracted ray to bend away from the normal.

4.8 - outline how total internal reflection is used in optical fibres

Optical fibers are made from thin cylindrical strands of high purity glass. These optical fibres are made so that they have a central high refractive index region called refractive index glass. The fibre consists of two concentric layers of ultra pure, bubble free glass. The centre fibre has the higher refractive index and the cladding has a lower refractive index, hence fulfilling the conditions for total internal reflection.

ADV: by using a group of fibres in a cable, large amounts of information can be sent

at one time IT travels at the speed of light It can bend around corners so it is not limited to the line of sight

communication The energy is forever strong and is trapped inside the cable forever.

Identify types of communication data that are stored or transmitted in digital form

The trend in communication signalling is towards digital transmission and storage. Almost all long-range communications systems now in use are transmitting the signal as a digital pulse. Reasons for favouring this include: enhanced security, and the ability to preserve the signal and still be able to read it after it has suffered more interference and superposition than is the case with analogue signals.• Optical fibres communication systems for transmitting data or sound use special lasers to transmit messages that are encoded as pulses of lights. • Things that use and store information digitally include: the compact disc (CD), DVDs, global positioning system (GPS), and the Internet.

Identify data sources gather process and present information from secondary sources to identify areas of current research and use the available evidence to discuss some of the underlying physical principles used in one application of physics related to waves such as

CD technology

1. The compact disc rotates at high and speed so that data is read at the same

regardless of the laser detector's position.

2. A beam is emitted by the laser and directed onto a single track on the disc by the

prism/beam splitter.

3. As the disc rotates, the beam encounters a series of pits and landings, the beam is

reflected back into the photo sensor to generate binary code (1=pit, 0=landing).

4. A simulated bit reader continuously streams the binary code as it is retrieved

from the disc.