Waves

11
WavesWaves
Refraction
Diffraction
Interference
Reflection

2
1.11.1
Understanding wavesUnderstanding waves

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
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
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
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
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
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
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
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
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

1212
Transverse waveTransverse wave

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
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
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

1616
Longitudinal WaveLongitudinal Wave

17
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

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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
Examples of longitudinal wavesExamples of longitudinal waves
Sound wavesSound waves
Ultrasonic waves ( High frequency soundUltrasonic waves ( High frequency sound
wave)wave)

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Transverse Waves vs LongitudinalTransverse Waves vs Longitudinal
WavesWaves
The differences between the two can beThe differences between the two can be
seenseen

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.

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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

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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.

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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
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.

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 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

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A loaded spring oscillating about its meanA loaded spring oscillating about its mean
positions is another example.positions is another example.

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
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

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Displacement/Time Graph of waveDisplacement/Time Graph of wave

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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

34
Examples of oscillatingExamples of oscillating
systemsystem

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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
 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

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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

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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

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 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
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
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

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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.

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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.

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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
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
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

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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

4949

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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
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
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
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
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
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
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
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?

5858
1.2 Reflection of Waves1.2 Reflection of Waves

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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
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.

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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
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
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
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

6565
1.3 Refraction of Waves1.3 Refraction of Waves

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
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
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
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
Refraction – slow to fast mediumRefraction – slow to fast medium

71
Refraction – fast to slow mediumRefraction – fast to slow medium

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
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
Water wave refraction patternsWater wave refraction patterns

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
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
 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
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
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
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
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

8282
1.4 Diffraction of Waves1.4 Diffraction of Waves

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
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..

87
Single slit diffraction patternSingle slit diffraction pattern

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
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
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
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

9292
1.5 Interference of Waves1.5 Interference of Waves

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
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
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
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

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
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

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
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
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
Interference PatternInterference Pattern

105
Interference equationInterference equation

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
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
Young experimentYoung experiment
http://www.youtube.com/watch?v=AMBcgVlamhttp://www.youtube.com/watch?v=AMBcgVlam

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

110110
1.6 Sound Waves1.6 Sound Waves

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
Tuning fork producing sound wavesTuning fork producing sound waves

113
Loudness and PitchLoudness and Pitch

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
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

116116
1.7 Electromagnetic waves1.7 Electromagnetic waves

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

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
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
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

122122
Important Formula ofImportant Formula of
WavesWaves

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