waves are carriers of energy

1. Current technologies associated with information transfer may use waves of one form or another waves are carriers of energy Describe the energy transformations required in one of the following:– fixed telephone – mobile telephone – fax/modem– radio and television – information storage systems images from SciArt e.g. Transmitting a voice message on a mobile phone: SOUND ENERGY ELECTRICAL ENERGY ELECTROMAGNETIC RADIATION (RADIO WAVES) Soundtrack: “Bitter Sweet Symphony”

Waves are a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

Features of a wave include frequency, wavelength and speed l v = f ‘medium’, ‘displacement’, ‘amplitude’, ‘period’, ‘compression’, ‘rarefaction’, ‘crest’, ‘trough’, ‘transverse waves’, images from SciArt for one source, f does not change when medium does Given s vs t and s vs x can we work out v? what wavelength is 96.1 MHz???????

Mechanical waves require a medium for propagation while electromagnetic waves do not! Electromagnetic waves are oscillating perpendicular electric and magnetic fields All electromagnetic waves move at the speed of light images from Microsoft Encarta

IN TRANSVERSE WAVES THE PARTICLES IN THE MEDIUM MOVE PERPENDICULAR TO THE DIRECTION OF PROPOGATION They move well through solids and on the surface of liquids but not through liquids or gases because of loose bonds between particles Describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves IN LONGITUDINAL WAVES THE PARTICLES IN THE MEDIUM OSCILLATE PARALLEL TO THE DIRECTION OF PROPOGATION images from SciArt

2. Sound waves can be used to illustrate many of theproperties of waves that are utilised in communication technologies sound waves are vibrations or oscillations of particles in a medium discuss the effect of density of the medium on the transmission speed of sound waves The velocity of sound in many other gases depends only on their density. If the molecules are heavy, they move less readily, and sound progresses through such a medium more slowly images from SciArt Sound generally moves much faster in liquids and solids than in gases. In both liquids and solids, density has the same effect as in gases; that is, velocity varies inversely as the square root of the density.

Relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves AIR PRESSURE Explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

An echo is a reflection of a sound wave Sonar, acronym for SOund Navigation And Ranging, a detection system based on the reflection of underwater sound waves— just as radar is based on the reflection of radio waves in the air. Distance is worked out from t assuming constant v in water

describe the effect of different materials on the reflection and absorption of sound describe the transfer of energy involved in the absorption of sound images from SciArt

Describe the principle of superposition and compare the resulting waves to the original waves in sound When a crest meets a crest, the waves add When a crest meets a trough, the waves cancel

3. Recent technological developments have allowed greater use of waves in the electromagnetic spectrum that do not require a medium for propagation All electromagnetic waves move at the speed of light Electromagnetic radiation exists at a range of different frequencies and wavelengths - - a whole SPECTRUM! Electromagnetic radiation has some everyday uses and effects, including applications in communication technology images from SciArt

e.g. eye or photographic film for light, thermometer for infra-red, Geiger counter for Gamma rays Identify some methods of detection for a number of wave bands from the electromagnetic spectrumExplain that the penetrating power of electromagnetic waves is related to differences in frequency or wavelength Low frequency electromagnetic radiation penetrates the atmosphere better than high frequency. e.g. sunsets look red because you are looking at the light through more atmosphere Explain that the relationship between the intensity of electromagnetic radiation and distance from a source (for a large distance) is an example of the inverse square lawI prop. to 1/d 2. Discuss limitations of the use of electromagnetic waves for communication purposes Outline how the modulation of amplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit information AMPLITUDE MODULATION FREQUENCY MODULATION

Caroline Chisholm College Physics Electromagnetic radiation of different wavelengths is absorbed by different amounts in the atmosphere. Wavebands which are absorbed are therefore not easily detected from ground-based systems, so space telescopes (such as the Hubble Space Telescope) are preferable. Very short wavelength radiation such as X-rays and Gamma rays interact with and are absorbed by oxygen and nitrogen in the atmosphere Most Ultraviolet (UV) radiation interacts with ozone and so cannot reach the ground. Infrared radiation interacts with water vapour and carbon dioxide and so is (incompletely) absorbed by the atmosphere Long waves interact with electrons in the ionosphere So only near-UV, visible light, near-Infrared, radio and microwaves make it to the ground with out much absorption by the atmosphere. All others are more easily detectable from space

4. Many communication technologies use applications of reflection and refraction of electromagnetic waves REFLECTION ANGLE OF INCIDENCE=ANGLE OF REFLECTION describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer e.g. fibre optics, satellite dishes, radio telescopes, orbitting satellites etc.

Describe one application of reflection for each of the following: plane surfaces Bathroom mirror SHOP MIRRORS concave surfacesconvex surfaces images from SciArt Radio waves can diffract around objects and are reflected by the ionosphere and the ground, so they could be sent around the world even before there were satellites. However, reliability depends on the time of the day, the position of the sun, solar winds and losses of intensity over distance.

Describe refraction in terms of the bending of the wavefront passing from one medium to anotherExplain that refraction is related to the different velocities exhibited by a wave in two media images from SciArt

refractive index is the ratio of v1 to v2 Define refractive index in terms of changes in the velocity of a wave in passing from one medium to anotherDefine and discuss the application of Snell’s Law:v1/v2 = (sin i)/(sin r) = refractive index so if we know the refractive index when moving from medium 1 to medium 2, we can compare the velocities of light in the two mediums (angles always measured from normal) Identify the conditions necessary for total internal reflection and determine critical angleOutline how refraction and/or total internal reflection are used in technologies such as lenses or optical fibres

5. Other properties of electromagnetic waves have potential for future communication technologies and data storage technologies Identify types of communication data that are stored or transmitted in digital form e.g. CD DVD Computer disks

Discuss the developments in technology that allowed the production of communication technologies, such as CD technology and Global Positioning Systems e.g. CDs use electromagnetic radiation (laser light) to reflect off pits in the CD surface. The intensity of the reflected light provides a varying signal which is changed to a binary code of numbers which can be used to create the signal amplitude of the music or video.

waves are carriers of energy