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Waves Chapter 1 Form 5

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  • http://www.s-cool.co.uk/gcse/physics/properties-of-waves/revise-it/refraction-of-waves

Transcript

  • 1. 11 WavesWaves Refraction Diffraction Interference Reflection
  • 2. 2 1.11.1 Understanding wavesUnderstanding waves
  • 3. 3 The nature of wavesThe nature of waves Have you ever thrown a stone into aHave you ever thrown a stone into a pond? What did you see?pond? What did you see?
  • 4. 4 Waves are everywhere in natureWaves are everywhere in nature  Sound waves,Sound waves,  visible light waves,visible light waves,  radio waves,radio waves,  microwaves,microwaves,  water waveswater waves  telephone chordtelephone chord waves,waves,  stadium waves,stadium waves,  earthquake waves,earthquake waves,  waves on a stringwaves on a string
  • 5. 5 What is a wave?What is a wave? A wave is aA wave is a travelling disturbancetravelling disturbance or aor a motion of a disturbance, from amotion of a disturbance, from a vibrating or oscillating source. As avibrating or oscillating source. As a wave travels, itwave travels, it carries energycarries energy alongalong with it in the direction of thewith it in the direction of the propagation.propagation.
  • 6. 6 What is wave?What is wave? An oscillating or vibrating motion in whichAn oscillating or vibrating motion in which a point or body moves back and fortha point or body moves back and forth along a line about a fixed central pointalong a line about a fixed central point produces WAVES.produces WAVES. An oscillating or vibrating system acts as aAn oscillating or vibrating system acts as a source of waves whichsource of waves which transfer energytransfer energy from one point to another withoutfrom one point to another without transferring matter.transferring matter.
  • 7. 7 Oscillating SystemsOscillating Systems Examples of oscillating systemExamples of oscillating system What is a complete oscillation? From point B to C and back to B The time taken to make one oscillation = the period, T
  • 8. 8 Type of WavesType of Waves List a few type of waves and their sourcesList a few type of waves and their sources if you remember?if you remember?  Light – Vibration of electrons in atomLight – Vibration of electrons in atom  Sound – Vibration of mechanical bodies e.gSound – Vibration of mechanical bodies e.g guitar strings.guitar strings.  Water wave – Disturbance or vibration on aWater wave – Disturbance or vibration on a still water surface.still water surface.  Electromagnetic wave – Oscillation orElectromagnetic wave – Oscillation or vibration between electric field and magneticvibration between electric field and magnetic field.field.
  • 9. 9 Propagation of WavesPropagation of Waves When a wave travels through a medium,When a wave travels through a medium, the particles of the medium vibrate aboutthe particles of the medium vibrate about their equilibrium positions.their equilibrium positions. However, the particles of the mediumHowever, the particles of the medium dodo not travelnot travel in the direction of the wave.in the direction of the wave. A wave transfer energy and theA wave transfer energy and the momentum from the source of the wave tomomentum from the source of the wave to the surroundings.the surroundings.
  • 10. 10 IntroductionIntroduction Wave is caused by vibrations orWave is caused by vibrations or oscillations.oscillations. It transports energy without permanentlyIt transports energy without permanently displacing the mediumdisplacing the medium Wave can be a mechanical wave such asWave can be a mechanical wave such as sound wave, which require medium tosound wave, which require medium to travel or electromagnetic wave which doestravel or electromagnetic wave which does not require a medium to travelnot require a medium to travel
  • 11. 11 Waves:Waves: Two types of wavesTwo types of waves Example: water waves, light waves Example: sound waves What are their similarities? Produced by oscillation, or vibration Transfer enegry or momentum without transferring matter Propagated by vibration or oscillation of the particles of the medium Transverse wave Longitudinal wave
  • 12. 1212 Transverse waveTransverse wave
  • 13. 13 Transverse wavesTransverse waves In a transverse wave the pulse travelsIn a transverse wave the pulse travels perpendicular to the disturbanceperpendicular to the disturbance..
  • 14. 14 Transverse WavesTransverse Waves Transverse waves occur when we wiggleTransverse waves occur when we wiggle the slinky back and forth.the slinky back and forth. They also occur when the sourceThey also occur when the source disturbance follows a periodic motion.disturbance follows a periodic motion. A spring or a pendulum can accomplishA spring or a pendulum can accomplish this.this. The wave formed here is a SINE wave.The wave formed here is a SINE wave.  http://webphysics.davidson.edu/course_material/py130/demo/illustration16_2.htmlhttp://webphysics.davidson.edu/course_material/py130/demo/illustration16_2.html
  • 15. 15 Example of transverse waveExample of transverse wave Radio wavesRadio waves Light wavesLight waves Water wavesWater waves Electromagnetic waves such as gammaElectromagnetic waves such as gamma raysrays
  • 16. 1616 Longitudinal WaveLongitudinal Wave
  • 17. 17 Longitudinal WaveLongitudinal Wave In a longitudinal wave the pulse travels inIn a longitudinal wave the pulse travels in a direction parallel to the disturbance.a direction parallel to the disturbance. http://www.physicsclassroom.com/mmedia/waves/lw.cfm
  • 18. 18 Longitudinal WaveLongitudinal Wave The wave we see here is aThe wave we see here is a longitudinal wave.longitudinal wave. The medium particles vibrate parallelThe medium particles vibrate parallel to the motion of the pulseto the motion of the pulse.. This is the same type of wave that weThis is the same type of wave that we use to transfer sound.use to transfer sound.  show tuning fork demoshow tuning fork demo
  • 19. 19 Examples of longitudinal wavesExamples of longitudinal waves Sound wavesSound waves Ultrasonic waves ( High frequency soundUltrasonic waves ( High frequency sound wave)wave)
  • 20. 20 Transverse Waves vs LongitudinalTransverse Waves vs Longitudinal WavesWaves The differences between the two can beThe differences between the two can be seenseen
  • 21. 21 Wave in a SpringWave in a Spring The wave that travels along the springThe wave that travels along the spring consists of compression and rarefraction.consists of compression and rarefraction.
  • 22. 22 Compression and rarefractionCompression and rarefraction Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart. These regions are known as compressions and rarefactions respectively. The compressions are regions of high air pressure while the rarefactions are regions of low air pressure. http://www.physicsclassroom.com/Class/so und/u11l1c.cfm
  • 23. 23 CompressionCompression AA compressioncompression is a point on a mediumis a point on a medium through which a longitudinal wave isthrough which a longitudinal wave is traveling that has the maximum density. Atraveling that has the maximum density. A region where the coils are spread apart,region where the coils are spread apart, thus maximizing the distance betweenthus maximizing the distance between coils, is known as a rarefaction.coils, is known as a rarefaction.
  • 24. 24 RarefactionRarefaction AA rarefactionrarefaction is a point on a mediumis a point on a medium through which a longitudinal wave isthrough which a longitudinal wave is traveling that has the minimum density.traveling that has the minimum density.
  • 25. 25 Oscillating SystemsOscillating Systems An oscillating system refers to a systemAn oscillating system refers to a system that undergoes a periodic to-and-frothat undergoes a periodic to-and-fro movement.movement.
  • 26. 26 Oscillating SystemsOscillating Systems  A simple pendulum:A simple pendulum:  A simple pendulum is an oscillating system.A simple pendulum is an oscillating system.  One complete oscillation of a pendulum: pendulumOne complete oscillation of a pendulum: pendulum ball moves from a position in such a way that it isball moves from a position in such a way that it is moving in the same direction again.moving in the same direction again.  http://www.animations.physics.unsw.edu.au/jw/oscillations.htmhttp://www.animations.physics.unsw.edu.au/jw/oscillations.htm
  • 27. 27 Oscillating SystemsOscillating Systems A loaded spring oscillating about its meanA loaded spring oscillating about its mean positions is another example.positions is another example.
  • 28. 28
  • 29. 29 Displacement/Distance graphDisplacement/Distance graph  A displacement-distance graph is also called a displacement-position graph. It showsA displacement-distance graph is also called a displacement-position graph. It shows the displacement of the particles at various positions at a certain time.the displacement of the particles at various positions at a certain time.  From a displacement-distance graph, we can directly read theFrom a displacement-distance graph, we can directly read the following information:following information:  amplitude of the waveamplitude of the wave  wavelength of the wavewavelength of the wave  locations of crests and troughs (for a transverse wave), orlocations of crests and troughs (for a transverse wave), or compressions and rarefactions (for a longitudinal wave)compressions and rarefactions (for a longitudinal wave) 
  • 30. 30 Displacement/Time GraphDisplacement/Time Graph  Unlike a displacement-position graph, a displacement-time graph describesUnlike a displacement-position graph, a displacement-time graph describes the displacement of ONE particle at various time at a certain position.the displacement of ONE particle at various time at a certain position.  From a displacement-time graph, we can directly read theFrom a displacement-time graph, we can directly read the following information:following information:  amplitude of the waveamplitude of the wave  period of the wave (and hence, the frequency)period of the wave (and hence, the frequency)  direction of motion of the particle at various timedirection of motion of the particle at various time  http://sciencecity.oupchina.com.hk/npaw/student/supplementary/1c-graph.ahttp://sciencecity.oupchina.com.hk/npaw/student/supplementary/1c-graph.a
  • 31. 31 Displacement/Time Graph of waveDisplacement/Time Graph of wave
  • 32. 32 Displacement/Time graph of a waveDisplacement/Time graph of a wave Amplitude, A = a cm Period of oscillation, T is the time interval between points
  • 33. 33 FormulasFormulas
  • 34. 34 Examples of oscillatingExamples of oscillating systemsystem
  • 35. 35 Anatomy of a WaveAnatomy of a Wave Now we can begin to describe theNow we can begin to describe the anatomy of our waves.anatomy of our waves. We will use a transverse wave to describeWe will use a transverse wave to describe this since it is easier to see the pieces.this since it is easier to see the pieces.
  • 36. 36 Anatomy of a WaveAnatomy of a Wave  In our wave here the dashed line represents theIn our wave here the dashed line represents the equilibrium position.equilibrium position.  Once the medium is disturbed, it moves away from thisOnce the medium is disturbed, it moves away from this position and then returns to itposition and then returns to it
  • 37. 37 Anatomy of a WaveAnatomy of a Wave The points A and F are called theThe points A and F are called the CRESTSCRESTS of the wave.of the wave. This is the point where the waveThis is the point where the wave exhibits the maximum amount ofexhibits the maximum amount of positive or upwards displacementpositive or upwards displacement crest
  • 38. 38 Anatomy of a WaveAnatomy of a Wave The points D and I are called theThe points D and I are called the TROUGHSTROUGHS of the wave.of the wave. These are the points where the waveThese are the points where the wave exhibits its maximum negative orexhibits its maximum negative or downward displacement.downward displacement. trough
  • 39. 39 Anatomy of a WaveAnatomy of a Wave  The distance between two consecutive similarThe distance between two consecutive similar points (in this case two crests) is called thepoints (in this case two crests) is called the wavelengthwavelength..  This is the length of the wave pulse.This is the length of the wave pulse.  Between what other points is can aBetween what other points is can a wavelength be measured?wavelength be measured? wavelength
  • 40. 40 Anatomy of a WaveAnatomy of a Wave What else can we determine?What else can we determine? We know that things that repeat have aWe know that things that repeat have a frequency and a period. How could wefrequency and a period. How could we find a frequency and a period of afind a frequency and a period of a wave?wave?
  • 41. 41 Anatomy of a WaveAnatomy of a Wave The distance between the dashed lineThe distance between the dashed line and point A is called theand point A is called the AmplitudeAmplitude ofof the wave.the wave. This is the maximum displacement thatThis is the maximum displacement that the wave moves away from itsthe wave moves away from its Amplitude
  • 42. 42 Wave frequencyWave frequency We know that frequency measure howWe know that frequency measure how often something happens over a certainoften something happens over a certain amount of time.amount of time. We can measure how many times a pulseWe can measure how many times a pulse passes a fixed point over a given amountpasses a fixed point over a given amount of time, and this will give us the frequency.of time, and this will give us the frequency.
  • 43. 43 Wave frequencyWave frequency Suppose I wiggle a slinky back and forth,Suppose I wiggle a slinky back and forth, and count that 6 waves pass a point in 2and count that 6 waves pass a point in 2 seconds. What would the frequency be?seconds. What would the frequency be? 3 cycles / second3 cycles / second 3 Hz3 Hz we use the term Hertz (Hz) to stand for cycleswe use the term Hertz (Hz) to stand for cycles per second.per second.
  • 44. 44 Wave PeriodWave Period The period describes the same thing as itThe period describes the same thing as it did with a pendulum.did with a pendulum. It is the time it takes for one cycle toIt is the time it takes for one cycle to complete.complete. It also is the reciprocal of the frequency.It also is the reciprocal of the frequency. T = 1 / fT = 1 / f f = 1 / Tf = 1 / T let’s see if you get itlet’s see if you get it..
  • 45. 45 Wave SpeedWave Speed We can use what we know to determineWe can use what we know to determine how fast a wave is moving.how fast a wave is moving. What is the formula for velocity?What is the formula for velocity? velocity = distance / timevelocity = distance / time What distance do we know about a waveWhat distance do we know about a wave wavelengthwavelength and what time do we knowand what time do we know periodperiod
  • 46. 46 Wave SpeedWave Speed so if we plug these in we getso if we plug these in we get velocity =velocity = length of pulse /length of pulse / time for pulse to move pass a fixed pointtime for pulse to move pass a fixed point v =v = λλ / T/ T we will use the symbolwe will use the symbol λλ to representto represent wavelengthwavelength
  • 47. 47 Wave SpeedWave Speed v =v = λλ / T/ T but what does T equalbut what does T equal T = 1 / fT = 1 / f so we can also writeso we can also write v = fv = f λλ velocity = frequency * wavelengthvelocity = frequency * wavelength This is known as the wave equationThis is known as the wave equation.. examplesexamples
  • 48. 48 WavefrontsWavefronts
  • 49. 4949 Oscillating SystemsOscillating Systems
  • 50. 50 DampingDamping  DampingDamping  The decrease in amplitude of an oscillatingThe decrease in amplitude of an oscillating systemsystem  When its energy is drained out as heat energyWhen its energy is drained out as heat energy  External damping- overcoming frictionalExternal damping- overcoming frictional energyenergy  Internal damping- extension and compressionInternal damping- extension and compression of molecules in the systemof molecules in the system  Example of damping: simple pendulum, loadedExample of damping: simple pendulum, loaded spring, oscillating float, oscillating hacksawspring, oscillating float, oscillating hacksaw blade.blade.
  • 51. 51 DAMPINGDAMPING  Damping occurs when theDamping occurs when the swing will oscillate with aswing will oscillate with a smaller and smallersmaller and smaller amplitude and eventuallyamplitude and eventually stop.stop.  A System oscillates at itsA System oscillates at its natural frequency when nonatural frequency when no external force is applied onexternal force is applied on itit
  • 52. 52 Example of resonanceExample of resonance  Pushing a person in a swing in time with thePushing a person in a swing in time with the natural interval of the swing (its resonantnatural interval of the swing (its resonant frequency) will make the swing go higher andfrequency) will make the swing go higher and higher (maximum amplitude), while attempts tohigher (maximum amplitude), while attempts to push the swing at a faster or slower tempo willpush the swing at a faster or slower tempo will result in smaller arcs.result in smaller arcs.  This is because the energy the swing absorbs isThis is because the energy the swing absorbs is maximized when the pushes are "inmaximized when the pushes are "in phasephase" with" with the swing's natural oscillations, while some ofthe swing's natural oscillations, while some of the swing's energy is actually extracted by thethe swing's energy is actually extracted by the opposing force of the pushes when they are not.opposing force of the pushes when they are not.
  • 53. 53 ResonanceResonance Resonance occurs when a system isResonance occurs when a system is made to oscillate atmade to oscillate at a frequencya frequency equivalent to its natural frequencyequivalent to its natural frequency byby anan external forceexternal force.. The resonating system oscillates at itsThe resonating system oscillates at its maximum amplitude.maximum amplitude. E.g Bartons Pendulum systemE.g Bartons Pendulum system http://www.youtube.com/watch?v=K-PAJ1SQMhttp://www.youtube.com/watch?v=K-PAJ1SQM
  • 54. 54 Examples of resonancesExamples of resonances  Opera singer breaks a wine glass with herOpera singer breaks a wine glass with her voice due to the effect of resonance.voice due to the effect of resonance.  Tacoma Narrow Bridge in USA collapsed inTacoma Narrow Bridge in USA collapsed in 1940 due to the effect of resonance.1940 due to the effect of resonance.  A moving bus produces excessive noise atA moving bus produces excessive noise at certain speed when the frequency of thecertain speed when the frequency of the engine equal to the natural frequency of theengine equal to the natural frequency of the bus.bus.
  • 55. 55 Applications of resonanceApplications of resonance  Marching soldiers on a bridge. ResonanceMarching soldiers on a bridge. Resonance occurs when the rate of marching mathces theoccurs when the rate of marching mathces the natural frequency of the oscillation of a bridge.natural frequency of the oscillation of a bridge.  Wind instruments when air blown causesWind instruments when air blown causes resonance and produced music.resonance and produced music.  A radio receiver can be tuned to the sameA radio receiver can be tuned to the same frequency as the incoming radio waves,frequency as the incoming radio waves, transmitted by the radio stations, to set it intotransmitted by the radio stations, to set it into resonance so that large current is induced. Theresonance so that large current is induced. The induced current is amplified and converted toinduced current is amplified and converted to sound.sound.
  • 56. 56 Wave BehaviorWave Behavior Now we know all about waves.Now we know all about waves. How to describe them, measure them andHow to describe them, measure them and analyze them.analyze them. But how do they interact?But how do they interact?
  • 57. 57 Wave BehaviorWave Behavior We know that waves travel throughWe know that waves travel through mediums.mediums. But what happens when that medium runsBut what happens when that medium runs out? Or what happens when waves areout? Or what happens when waves are reflected, refracted, diffracted orreflected, refracted, diffracted or interfered?interfered?
  • 58. 5858 1.2 Reflection of Waves1.2 Reflection of Waves
  • 59. 59 Reflection of WavesReflection of Waves  Reflection is a wave phenomenon - AllReflection is a wave phenomenon - All waves can be reflectedwaves can be reflected . Reflection occurs. Reflection occurs when all or part of the waves are returned whenwhen all or part of the waves are returned when the waves encounter or hit an obstacle.the waves encounter or hit an obstacle.  When waves are reflected, theirWhen waves are reflected, their directiondirection ofof traveltravel changeschanges. Since waves direction changes,. Since waves direction changes, velocityvelocity of the wavesof the waves changeschanges..  When reflection occurs: The wavesWhen reflection occurs: The waves speedspeed v,v, frequencyfrequency f andf and wavelengthwavelength ww remains theremains the samesame (v = wf).(v = wf).  http://www.youtube.com/watch?feature=player_embedded&v=HFckyHq594http://www.youtube.com/watch?feature=player_embedded&v=HFckyHq594I
  • 60. 60 Application of reflection of wavesApplication of reflection of waves  Echoes are caused by the reflection ofEchoes are caused by the reflection of sound. A sound wave will continue tosound. A sound wave will continue to bounce around or reverberate until it hasbounce around or reverberate until it has lost all its energy. A wave loses some of itslost all its energy. A wave loses some of its energy when it hits an objects before beingenergy when it hits an objects before being reflected. The energy can be lost as heat -reflected. The energy can be lost as heat - the amplitude of reflected sound wave andthe amplitude of reflected sound wave and thus loudness of the sound getthus loudness of the sound get progressively lower over time.progressively lower over time.
  • 61. 61 Application of reflectionApplication of reflection  The phenomenon of the reflection ofThe phenomenon of the reflection of sound is used to determine thesound is used to determine the distance between the two objects, fordistance between the two objects, for example depth of seabed, depth ofexample depth of seabed, depth of cave or width of a valley. The type ofcave or width of a valley. The type of sound used depend on the media insound used depend on the media in which the sound wave is to travel: Forwhich the sound wave is to travel: For examples, for normal echoes throughexamples, for normal echoes through air, normal audible sound can beair, normal audible sound can be used; whereas, to penetrate humanused; whereas, to penetrate human body, sea bed and the likes,body, sea bed and the likes, ultrasound of higher frequency/energyultrasound of higher frequency/energy is used.is used.
  • 62. 62 Note about past year question 2011Note about past year question 2011 q32.q32.  Which statement is correct when water wavesWhich statement is correct when water waves are reflected by a reflector? The answerare reflected by a reflector? The answer shouldshould notnot be A "The velocity of water waves beforebe A "The velocity of water waves before and after reflection are the same" as erroneouslyand after reflection are the same" as erroneously given by a renowned publisher of Past Yeargiven by a renowned publisher of Past Year Questions. ItQuestions. It should be Cshould be C "The amplitude of"The amplitude of the water waves becomes smaller afterthe water waves becomes smaller after reflection (due to damping and imperfectreflection (due to damping and imperfect reflection or return of all wave energy as somereflection or return of all wave energy as some waves energy is transformed to other forms ofwaves energy is transformed to other forms of energy - e.g. heat and/or sound)energy - e.g. heat and/or sound)
  • 63. 63 Summary of Reflection of WaveSummary of Reflection of Wave  Reflection occurs when a wave bounces fromReflection occurs when a wave bounces from the surface of an obstacle.the surface of an obstacle.  None of the properties of a wave are changed byNone of the properties of a wave are changed by reflection.reflection.  The wavelength, frequency, period andThe wavelength, frequency, period and speedspeed are same before and after reflection.are same before and after reflection.  The only change is the direction in which theThe only change is the direction in which the wave is travelling.wave is travelling.
  • 64. 64 Characteristics of Reflected waves:Characteristics of Reflected waves: Angle of reflectionAngle of reflection The angle of reflection rThe angle of reflection r is equal to the angle ofis equal to the angle of incidence, iincidence, i SpeedSpeed unchangedunchanged WavelengthWavelength unchangedunchanged FrequencyFrequency unchangedunchanged Direction of waveDirection of wave Changes after reflectionChanges after reflection
  • 65. 6565 1.3 Refraction of Waves1.3 Refraction of Waves
  • 66. 66 Refraction of WavesRefraction of Waves  RefractionRefraction of wavesof waves occursoccurs whenwhen waves move from one mediumwaves move from one medium to another mediumto another medium with awith a change in wave speedchange in wave speed withoutwithout any change in wave frequencyany change in wave frequency .. The direction may or may notThe direction may or may not change depending on the angle ofchange depending on the angle of incidence i` (If i` > 0`, thenincidence i` (If i` > 0`, then directiondirection changes too.)changes too.)  ThisThis change in speedchange in speed withoutwithout change in frequency can onlychange in frequency can only comecome about withabout with a correspondinga corresponding change in wavelengthchange in wavelength of theof the waves because wave speed v =waves because wave speed v = wavelength w x waves frequency f (vwavelength w x waves frequency f (v = wf).= wf).
  • 67. 67 Refraction of waveRefraction of wave  WavesWaves speed and wavelength decreasespeed and wavelength decrease if theif the waveswaves move from a less dense medium (ormove from a less dense medium (or deeper water) to denser medium (or shallowerdeeper water) to denser medium (or shallower water)water); and, conversely,  the waves; and, conversely,  the waves speed andspeed and wavelength increasewavelength increase if the waves move from aif the waves move from a denser medium (or shallower water)denser medium (or shallower water) toto a lessa less dense medium (or deeper water)dense medium (or deeper water) ..  Decrease of wavelength w (and thus speed, sinceDecrease of wavelength w (and thus speed, since frequency f remains unchanged: v = wf) meansfrequency f remains unchanged: v = wf) means successive wavefronts get closer; and, conversely,successive wavefronts get closer; and, conversely, increase in wavelength (and thus wave speed) meansincrease in wavelength (and thus wave speed) means the wavefronts get further apartthe wavefronts get further apart
  • 68. 68 Refraction of waveRefraction of wave  No change in wave directionNo change in wave direction IF the angle ofIF the angle of incident i` of the waves as they enter anotherincident i` of the waves as they enter another medium is zero (i.e. parallel to the normal).medium is zero (i.e. parallel to the normal).  Remember, the waves speed and wavelengthRemember, the waves speed and wavelength changes.changes.  Note: TheNote: The defining characteristics ofdefining characteristics of refractionrefraction IS NOT change in direction of theIS NOT change in direction of the waves BUTwaves BUT change in waves speed andchange in waves speed and wavelength without change of frequencywavelength without change of frequency as the waves move from one medium intoas the waves move from one medium into another mediumanother medium
  • 69. 69 Refraction wave characteristicsRefraction wave characteristics  Waves directionWaves direction onlyonly changes IF the anglechanges IF the angle of incident i`of incident i` of the waves as they enter anotherof the waves as they enter another mediummedium is > zerois > zero. When i` > 0`:. When i` > 0`:  waves directionwaves direction bends towards normalbends towards normal if theif the waveswaves move from a less dense medium (ormove from a less dense medium (or deeper water) to denser medium (ordeeper water) to denser medium (or shallower water)shallower water) ;;  waves directionwaves direction bends away from normalbends away from normal if theif the waves move from awaves move from a denser medium (ordenser medium (or shallower water)shallower water) toto a less dense mediuma less dense medium (or deeper water)(or deeper water) .. http://physicsf45spm.blogspot.com/2012/03/refraction-of-water-waves.html
  • 70. 70 Refraction – slow to fast mediumRefraction – slow to fast medium
  • 71. 71 Refraction – fast to slow mediumRefraction – fast to slow medium
  • 72. 72 Changes of direction in refractionChanges of direction in refraction As the light wave goes into the block it slows down and bends towards the normal line, so angle A is always bigger than angle B. As the ray comes out of the block the light wave speeds up again and bends away from the normal line, so angle B is always smaller than angle C. The only time light waves do not bend when changing speed, is if they are travelling along the normal line, at right angles to the boundary.
  • 73. 73 Critical angleCritical angle  Critical angleCritical angle , c is defined as the, c is defined as the angleangle of incidence in the denser mediumof incidence in the denser medium when the angle of refraction, r in thewhen the angle of refraction, r in the less dense medium is 90 degree.less dense medium is 90 degree.
  • 74. 74 Water wave refraction patternsWater wave refraction patterns
  • 75. 75 Why sound can be heard over aWhy sound can be heard over a longer distance on a cold nightlonger distance on a cold night compared with a hot day?compared with a hot day?
  • 76. 76 Explanation:Explanation:  On a hot day :On a hot day :  The hot surface of the earth causes the layerThe hot surface of the earth causes the layer of air near the surface to be warmer. Thisof air near the surface to be warmer. This causes sound waves to be refracted awaycauses sound waves to be refracted away from the earth.from the earth.  On a cool night :On a cool night :  The sound waves travel slower in the coolerThe sound waves travel slower in the cooler layer of air near the surface of the earth than inlayer of air near the surface of the earth than in the upper, warmer air. As a result, the wavesthe upper, warmer air. As a result, the waves are refracted towards the earth.are refracted towards the earth.
  • 77. 77  Why is the sea rough at the cape butWhy is the sea rough at the cape but calm at the bay?calm at the bay?  As water wave propagate from deepAs water wave propagate from deep region to the shallow region near theregion to the shallow region near the shore, part of wave in shallow watershore, part of wave in shallow water slows down, part of wave in deeperslows down, part of wave in deeper water moves more quickly.water moves more quickly.  As a result refraction of wave takesAs a result refraction of wave takes place and wave bends.place and wave bends.  Wave energy is converged towards theWave energy is converged towards the cape (headland) but diverged awaycape (headland) but diverged away from the bay. Wave energy dissipatedfrom the bay. Wave energy dissipated in bays. Therefore sea is rough at thein bays. Therefore sea is rough at the cape but calm at the bay.cape but calm at the bay.
  • 78. 78 Why is the sea rough at the cape butWhy is the sea rough at the cape but calm or stationary at the bay?calm or stationary at the bay?
  • 79. 79 Reasons:Reasons: The depth of water varies across the bayThe depth of water varies across the bay areaarea The energy of the water waves sreads to aThe energy of the water waves sreads to a wider area as compared to the region nearwider area as compared to the region near cape.cape. The amplitude of the water wave near theThe amplitude of the water wave near the bay is low hence water is comparativelybay is low hence water is comparatively stillstill
  • 80. 80 Summary of RefractionSummary of Refraction Refraction occurs when a wave moves from oneRefraction occurs when a wave moves from one material to another.material to another.  TheThe speed and wavelengthspeed and wavelength are changed byare changed by refraction.refraction.  TheThe frequency and period of the wavefrequency and period of the wave staystay the same.the same.  The direction in which the wave is travelling mayThe direction in which the wave is travelling may or may not be changed by refraction.or may not be changed by refraction.
  • 81. 81 Characteristic of RefractedCharacteristic of Refracted waveswaves Angle ofAngle of refractionrefraction Shallow waterShallow water to Deep waterto Deep water Angle of refraction lesserAngle of refraction lesser than angle of incidencethan angle of incidence Deep water toDeep water to shallow watershallow water Angle of refraction moreAngle of refraction more than angle of incidencethan angle of incidence SpeedSpeed Deep water:Deep water: fasterfaster ShallowShallow water: Slowerwater: Slower WavelengthWavelength Deep water:Deep water: longerlonger ShallowShallow water: shorterwater: shorter FrequencyFrequency unchangedunchanged unchangedunchanged Direction ofDirection of propagationpropagation ChangesChanges Refracted near toRefracted near to ChangesChanges Refracted far fromRefracted far from
  • 82. 8282 1.4 Diffraction of Waves1.4 Diffraction of Waves
  • 83. 83 Diffraction of WavesDiffraction of Waves DiffractionDiffraction refers to therefers to the spreadingspreading out of wavesout of waves as they move throughas they move through a gap or bend around an obstaclea gap or bend around an obstacle about theabout the size of the wavelengthsize of the wavelength or smalleror smaller..
  • 84. 84 DiffractionDiffraction  Diffraction is more visible when:Diffraction is more visible when:  􀂾􀂾 The wavelength of the wave is biggerThe wavelength of the wave is bigger  􀂾􀂾 The obstacle is smaller than the wavelengthThe obstacle is smaller than the wavelength  􀂾􀂾 The aperture is smaller than the wavelengthThe aperture is smaller than the wavelength  IN other words, if theIN other words, if the sizesize (of the gap, aperture(of the gap, aperture or obstacle) is significantlyor obstacle) is significantly largerlarger than thethan the wavelength, thewavelength, the effectseffects of diffraction wouldof diffraction would notnot bebe obviousobvious..
  • 85. 85 ApertureAperture
  • 86. 86 ObstacleObstacle
  • 87. 87 Single slit diffraction patternSingle slit diffraction pattern
  • 88. 88 Video/ animationVideo/ animation http://www.acoustics.salford.ac.uk/feschoohttp://www.acoustics.salford.ac.uk/feschoo ls/waves/diffract3.phpls/waves/diffract3.php
  • 89. 89 Diffraction of wavesDiffraction of waves No change in: frequency f,No change in: frequency f, wavelength and speed v of thewavelength and speed v of the waves;waves; ChangeChange in:in: directiondirection andand amplitudeamplitude aa of the waves upon diffraction. (Amplitudeof the waves upon diffraction. (Amplitude of diffracted waves < amplitude of incidentof diffracted waves < amplitude of incident waves; and direction of propagationwaves; and direction of propagation changes and the waves spread out)changes and the waves spread out)
  • 90. 90 Summary of DiffractionSummary of Diffraction  Diffraction occurs when a wave passes anDiffraction occurs when a wave passes an edge, passes through a narrow gap or goesedge, passes through a narrow gap or goes past an object.past an object.  None of the properties of a wave are changedNone of the properties of a wave are changed by diffraction. The wavelength, frequency,by diffraction. The wavelength, frequency, period and speed are same before and afterperiod and speed are same before and after diffraction. Again, the only change is thediffraction. Again, the only change is the amplitudeamplitude andand direction in which thedirection in which the wave is travellingwave is travelling ..  When a wave passes through a gap theWhen a wave passes through a gap the diffraction effect is greatest when the width ofdiffraction effect is greatest when the width of the gap is about the same size as thethe gap is about the same size as the wavelength of the wave.wavelength of the wave.
  • 91. 91 Diffraction causes:Diffraction causes: WaveWave characteristicscharacteristics Effects of diffractionEffects of diffraction SpeedSpeed unchangedunchanged WavelengthWavelength unchangedunchanged FrequencyFrequency unchangedunchanged Amplitude andAmplitude and Direction ofDirection of WaveWave changeschanges
  • 92. 9292 1.5 Interference of Waves1.5 Interference of Waves
  • 93. 93 InterferenceInterference Where two waves meet, their effects areWhere two waves meet, their effects are added together. This is calledadded together. This is called interferenceinterference.. No change in: Frequency f, wavelength w and speed v IF the waves are from coherent wave sources: Coherent waves are waves which maintain a constant phase difference and can be produced by 2 oscillating sources vibrating at the same frequency.
  • 94. 94 Principle of SuperpositionPrinciple of Superposition  The principle of superposition stateThe principle of superposition state that when two waves propagatethat when two waves propagate through the same point at the samethrough the same point at the same time, thetime, the displacement at that pointdisplacement at that point isis thethe vector sum of the displacement ofvector sum of the displacement of each individual wave.each individual wave. •• Two wave sources which areTwo wave sources which are coherentcoherent have thehave the same frequencysame frequency and theand the samesame phasephase or phase difference.or phase difference. •• The superposition effects createsThe superposition effects creates interferenceinterference
  • 95. 95 Constructive InterferenceConstructive Interference Let’s consider two waves moving towardsLet’s consider two waves moving towards each other, both having a positive upwardeach other, both having a positive upward amplitude.amplitude. What will happen when they meet?What will happen when they meet?
  • 96. 96 Constructive InterferenceConstructive Interference They willThey will ADDADD together to produce atogether to produce a greater amplitude.greater amplitude. This is known asThis is known as CONSTRUCTIVECONSTRUCTIVE INTERFERENCEINTERFERENCE..
  • 97. 97 Constructive InterferenceConstructive Interference
  • 98. 98 Destructive InterferenceDestructive Interference Now let’s consider the opposite, twoNow let’s consider the opposite, two waves moving towards each other, onewaves moving towards each other, one having a positive (upward) and one ahaving a positive (upward) and one a negative (downward) amplitude.negative (downward) amplitude. What will happen when they meet?What will happen when they meet?
  • 99. 99 Destructive InterferenceDestructive Interference This time when theyThis time when they addadd togethertogether they will produce a smaller amplitude.they will produce a smaller amplitude. This is know asThis is know as DESTRUCTIVEDESTRUCTIVE INTERFERENCEINTERFERENCE..
  • 100. 100 Destructive InterferenceDestructive Interference
  • 101. 101 Destructive interferenceDestructive interference When they arrive out of step, they cancelWhen they arrive out of step, they cancel out.out. This is calledThis is called destructive interferencedestructive interference ..
  • 102. 102 Effects of InterferenceEffects of Interference ::  ChangeChange inin amplitudeamplitude::  Constructive interferenceConstructive interference producesproduces maximummaximum amplitudeamplitude (max. crest or trough) at points of(max. crest or trough) at points of antinodesantinodes ;; Lines that join points of antinodes are known asLines that join points of antinodes are known as antinodalantinodal lineslines..  Destructive interferenceDestructive interference producesproduces zero amplitudezero amplitude atat points ofpoints of nodesnodes. Lines that join nodes are known as. Lines that join nodes are known as nodalnodal lineslines. . 
  • 103. 103 Interference in light and sound wavesInterference in light and sound waves Constructive interferenceConstructive interference Light - Bright fringesLight - Bright fringes Sound - Loud soundSound - Loud sound Destructive interferenceDestructive interference Light - Dark fringeLight - Dark fringe Sound - Soft soundSound - Soft sound
  • 104. 104 Interference PatternInterference Pattern
  • 105. 105 Interference equationInterference equation
  • 106. 106 Different FrequenciesDifferent Frequencies  Low frequency, largeLow frequency, large wavelength, value of xwavelength, value of x is largeris larger  High frequency, smallHigh frequency, small wavelength, value of xwavelength, value of x is smalleris smaller
  • 107. 107 Distance between sourcesDistance between sources  Larger distanceLarger distance between sourcesbetween sources  X value is smallerX value is smaller  Smaller distance betweenSmaller distance between sourcessources  X value is largerX value is larger
  • 108. 108 Young experimentYoung experiment http://www.youtube.com/watch?v=AMBcgVlamhttp://www.youtube.com/watch?v=AMBcgVlam
  • 109. 109 Diffraction is the constructive and destructive interference of two beams of light that results in a wave-like pattern Monochromatic light : Light with one colour/one wavelength e.g from laser pen
  • 110. 110110 1.6 Sound Waves1.6 Sound Waves
  • 111. 111 Sound WavesSound Waves Sound waves areSound waves are longitudinallongitudinal waves .waves . Sound waves are produced when aSound waves are produced when a vibrating object causes air moleculesvibrating object causes air molecules around it toaround it to vibratevibrate and producing aand producing a series ofseries of compressioncompression andand rarefactionrarefaction
  • 112. 112 Tuning fork producing sound wavesTuning fork producing sound waves
  • 113. 113 Loudness and PitchLoudness and Pitch
  • 114. 114 Application of Sound wave inApplication of Sound wave in submarinesubmarine a submarine transmitting ultrasonic waves directed at a big rock on the sea bed. After sometime, the submarine detects the wave again Submarine used ultrasonic wave but not ordinary sound wave because. 1. Ultrasonic has high frequency 2. Ultrasonic can be reflected easily
  • 115. 115 Other sound waves applications:Other sound waves applications:  2 other applications of sound waves.2 other applications of sound waves.  Sonar- using ultrasound to locateSonar- using ultrasound to locate underwater objectsunderwater objects ..  Ultrasound scanner – use to scanUltrasound scanner – use to scan and capture image of a fetus in aand capture image of a fetus in a mother’s wombmother’s womb
  • 116. 116116 1.7 Electromagnetic waves1.7 Electromagnetic waves
  • 117. 117 1.7 Analysing electromagnetic1.7 Analysing electromagnetic spectrum :spectrum : the electromagnetic spectrum microwave Visible light X - ray Electromagnetic wave is classified into types according to the frequency of the wave: these types include ( order of decreasing wavelength) RIVUXGa or Raju Mother InVites Us (as) Xmas Guest -12-9-5
  • 118. 118
  • 119. 119 Electromagnetic wavesElectromagnetic waves  Electromagnetic waves areElectromagnetic waves are transversetransverse waves ,consisting ofwaves ,consisting of electricelectric fields andfields and magnetic fields vibratingmagnetic fields vibrating perpendicularperpendicular to each other.to each other.  Gamma raysGamma rays has the highest frequencyhas the highest frequency and theand the shortestshortest wavelength.wavelength.
  • 120. 120 QuizQuiz  Which of the following shows theWhich of the following shows the arrangement of the electromagnetic waves inarrangement of the electromagnetic waves in descending order?descending order? A- A visible light, microwave, ultraviolet ray,A- A visible light, microwave, ultraviolet ray, infraredinfrared B- Microwave, visible light, ultraviolet ray,B- Microwave, visible light, ultraviolet ray, infraredinfrared C- Microwave, infrared ray, visible light,C- Microwave, infrared ray, visible light, ultraviolet rayultraviolet ray D- Visible light, ultraviolet ray, microwave,D- Visible light, ultraviolet ray, microwave, infrared rayinfrared ray
  • 121. 121 Properties of electromagnetic waves.Properties of electromagnetic waves.  They transfer energy from one place toThey transfer energy from one place to another.another.  They are transverse wavesThey are transverse waves  They can travel through a vacuumThey can travel through a vacuum  They travel at a speed of approximately 3 xThey travel at a speed of approximately 3 x 108 m s-1 in vacuum108 m s-1 in vacuum  They all show the wave properties :They all show the wave properties : reflection, refraction, diffraction andreflection, refraction, diffraction and interferenceinterference  They carry no chargeThey carry no charge  They can be emitted and absorbed byThey can be emitted and absorbed by mattermatter
  • 122. 122122 Important Formula ofImportant Formula of WavesWaves