Presentation on theme: "waves are carriers of energy"— Presentation transcript:
1 waves are carriers of energy 1. Current technologies associated withinformation transfer may use waves of one form or anotherwaves are carriers of energyimages from SciArtDescribe the energy transformations required in one of the following: – fixed telephone – mobile telephone – fax/modem – radio and television – information storage systemse.g. Transmitting avoice messageon a mobile phone:SOUNDENERGYELECTRICALENERGYELECTROMAGNETICRADIATION(RADIO WAVES)Soundtrack: “Bitter Sweet Symphony”
2 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
3 Features of a wave include frequency, wavelength and speed ‘medium’, ‘displacement’, ‘amplitude’, ‘period’, ‘compression’,‘rarefaction’, ‘crest’, ‘trough’, ‘transverse waves’,images from SciArtfor one source, f does not change when medium doesGiven s vs t and s vs x can we work out v?lv = fwhat wavelength is 96.1 MHz???????
4 Electromagnetic waves are oscillating perpendicular Mechanical waves require a medium for propagation while electromagnetic waves do not!Electromagnetic waves areoscillating perpendicularelectric and magnetic fieldsAll electromagnetic waves move at the speed of lightimages from Microsoft Encarta
5 IN TRANSVERSE WAVES THE PARTICLES IN THE MEDIUM Describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal wavesIN TRANSVERSE WAVES THE PARTICLES IN THE MEDIUMMOVE PERPENDICULAR TO THE DIRECTION OF PROPOGATIONThey move well through solids and on the surface of liquids but not through liquids or gases because of loose bonds between particlesIN LONGITUDINAL WAVES THE PARTICLES IN THE MEDIUMOSCILLATE PARALLEL TO THE DIRECTION OF PROPOGATIONimages from SciArt
6 sound waves are vibrations or oscillations of particles in a medium 2. Sound waves can be used to illustrate many of the properties of waves that are utilised in communication technologiessound waves are vibrations or oscillationsof particles in a mediumdiscuss the effect of density of the medium on the transmission speed of sound wavesThe 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 slowlyimages from SciArtSound 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.
7 Relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves AIRPRESSUREExplain qualitatively that pitch is related to frequency and volume to amplitude of sound waves
8 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
9 images from SciArtdescribe the effect of different materials on the reflection and absorption of sound describe the transfer of energy involved in the absorption of sound
10 a trough, the waves cancel Describe the principle of superposition and compare the resulting waves to the original waves in soundWhen a crest meetsa crest, the waves addWhen a crest meetsa trough, the waves cancel
11 All electromagnetic waves move at the speed of light 3. Recent technological developments have allowed greater use of waves in the electromagnetic spectrum that do not require a medium for propagationAll electromagnetic waves move at the speed of lightElectromagneticradiation exists at arange of differentfrequencies andwavelengths - -a whole SPECTRUM!Electromagnetic radiation has some everyday uses and effects, including applications in communication technologyimages from SciArt
12 e.g. eye orphotographic filmfor light,thermometer forinfra-red,Geiger counterfor Gamma raysIdentify some methods of detection for a number of wave bands from the electromagnetic spectrum Explain that the penetrating power of electromagnetic waves is related to differences in frequency or wavelengthLow frequency electromagnetic radiationpenetrates the atmosphere better than highfrequency. e.g. sunsets look red because youare looking at the light through more atmosphereExplain 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 law I prop. to 1/d 2.Discuss limitations of the use of electromagnetic waves for communication purposesOutline how the modulation of amplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit informationAMPLITUDEMODULATIONFREQUENCYMODULATION
13 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 raysinteract with and are absorbed by oxygen and nitrogen in the atmosphereMost Ultraviolet (UV) radiation interacts with ozone and so cannot reach the ground.Infrared radiation interacts with water vapour and carbon dioxideand so is (incompletely) absorbed by the atmosphereLong waves interact with electrons in the ionosphereSo only near-UV, visible light, near-Infrared, radio and microwavesmake it to the ground with out much absorption by the atmosphere.All others are more easily detectable from space
14 4. Many communication technologies use applications of reflection and refraction of electromagnetic wavesREFLECTIONANGLE OF INCIDENCE=ANGLE OF REFLECTIONdescribe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfere.g. fibre optics, satellite dishes, radio telescopes, orbitting satellites etc.
15 Describe one application of reflection for each of the following: plane surfacesBathroom mirrorSHOP MIRRORSconcave surfaces convex surfacesimages from SciArtRadio waves can diffract around objects and are reflected by the ionosphere and the ground, sothey could be sent around the world even before there were satellites. However, reliability dependson the time of the day, the position of the sun, solar winds and losses of intensity over distance.
16 Describe refraction in terms of the bending of the wavefront passing from one medium to another Explain that refraction is related to the different velocities exhibited by a wave in two mediaimages from SciArt
17 (angles always measured from normal) refractive index is the ratio of v1 to v2so if we know the refractive index when moving from medium 1 to medium 2,we can compare the velocities of light in the two mediumsDefine refractive index in terms of changes in the velocity of a wave in passing from one medium to another Define and discuss the application of Snell’s Law: v1/v2 = (sin i)/(sin r) = refractive index(angles alwaysmeasured from normal)Identify the conditions necessary for total internal reflection and determine critical angle Outline how refraction and/or total internal reflection are used in technologies such as lenses or optical fibres
18 e.g. CD DVD Computer disks 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 forme.g.CDDVDComputer disks
19 Discuss the developments in technology that allowed the production of communication technologies, such as CD technology and Global Positioning Systemse.g. CDs use electromagnetic radiation (laser light) to reflect off pitsin the CD surface. The intensity of the reflected light provides avarying signal which is changed to a binary code of numbers whichcan be used to create the signal amplitude of the music or video.