Wave Characteristics. Terms to Review Parts of a Wave – Crest – Trough – Pulse – Amplitude...
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Transcript of Wave Characteristics. Terms to Review Parts of a Wave – Crest – Trough – Pulse – Amplitude...
Wave CharacteristicsWave Characteristics
Terms to ReviewTerms to Review
Parts of a WaveParts of a Wave– CrestCrest– TroughTrough– PulsePulse– AmplitudeAmplitude– WavelengthWavelength– FrequencyFrequency– PeriodPeriod
Types of WavesTypes of Waves– Mechanical WavesMechanical Waves– Electromagnetic Electromagnetic
WavesWaves– Transverse WavesTransverse Waves– Longitudinal WavesLongitudinal Waves– Surface WavesSurface Waves
Calculations to KnowCalculations to Know
Speed of wave (velocity) Speed of wave (velocity) = freq x wavelength= freq x wavelength
Frequency = cycles/secondFrequency = cycles/secondPeriod = seconds/cyclePeriod = seconds/cycle
Frequency = 1/periodFrequency = 1/periodPeriod = 1/frequencyPeriod = 1/frequency
Characteristics of WavesCharacteristics of Waves
Amplitude of a wave is its maximum Amplitude of a wave is its maximum displacement from the rest or equilibrium displacement from the rest or equilibrium position.position.
Slinky WavesSlinky Waves
Hand of one partner = vibrating source of energyHand of one partner = vibrating source of energy Slinky = material medium through which energy is Slinky = material medium through which energy is
transferredtransferred Frequency of wave = number of complete cycles Frequency of wave = number of complete cycles
passing a given point in a unit of time (i.e. a second)passing a given point in a unit of time (i.e. a second) Frequency of wave is determined by the source Frequency of wave is determined by the source
(person)(person) Once a wave is produced, its frequency will never Once a wave is produced, its frequency will never
change (even if the speed and wavelength change)change (even if the speed and wavelength change) As wave travels through the slinky, its amplitude As wave travels through the slinky, its amplitude
usually decreases as some energy is lost to frictionusually decreases as some energy is lost to friction
Principle of SuperpositionPrinciple of Superposition
When two waves are travelling through a When two waves are travelling through a medium at same time (sent pulse from medium at same time (sent pulse from either direction)either direction)
Principle states that: displacement of a Principle states that: displacement of a medium caused by two or more waves is medium caused by two or more waves is the sum of the displacement caused by the the sum of the displacement caused by the individual wavesindividual waves
Result of superposition of two or more Result of superposition of two or more waves is called interference.waves is called interference.
Types of InterferenceTypes of Interference
1)1) Constructive InterferenceConstructive Interference
- two pulses travelling in the same direction- two pulses travelling in the same direction
- results in wave with a larger amplitude - results in wave with a larger amplitude that any of the individual wavesthat any of the individual waves
Types of InterferenceTypes of Interference
2) Destructive Interference2) Destructive Interference
- two pulses travelling in the opposite - two pulses travelling in the opposite directiondirection
- results in a wave with a smaller amplitude- results in a wave with a smaller amplitude
Wave Behaviour at Different Wave Behaviour at Different MediaMedia
Speed of wave depends only on properties of the Speed of wave depends only on properties of the mediummedium– Speed of water waves depends on depth of waterSpeed of water waves depends on depth of water– Speed of rope wave depends on force exerted on ropeSpeed of rope wave depends on force exerted on rope– Speed of sound wave depends on temperature of airSpeed of sound wave depends on temperature of air
This means, for a given medium, This means, for a given medium, – higher frequency = shorter wavelengthhigher frequency = shorter wavelength– lower frequency = longer wavelengthlower frequency = longer wavelength
Speed of wave = frequency x wavelength
Speed of Slinky WavesSpeed of Slinky Waves
Speed of wave doesn’t depend on amplitude Speed of wave doesn’t depend on amplitude or frequency of the wave...it only depends or frequency of the wave...it only depends on the properties of the medium.on the properties of the medium.
For example, you can’t make a sound wave For example, you can’t make a sound wave travel any faster by shouting quicker...the travel any faster by shouting quicker...the medium (air) is still the same. medium (air) is still the same.
Waves in Different MediaWaves in Different Media Design an experiment to test the speed of waves in Design an experiment to test the speed of waves in
different mediadifferent media Prove that the speed of waves depends only on the Prove that the speed of waves depends only on the
media – a wave in the same media will always have media – a wave in the same media will always have the same speedthe same speed
Hand in:Hand in:1)1) QuestionQuestion2)2) PredictionPrediction3)3) MaterialsMaterials4)4) ProcedureProcedure5)5) Data/ObservationsData/Observations6)6) ConclusionConclusion
Wave Behaviour in Different Wave Behaviour in Different MediaMedia
Waves typically move from one media to Waves typically move from one media to another (i.e. Light wave from air to water)another (i.e. Light wave from air to water)
When a wave (incident wave) reaches a When a wave (incident wave) reaches a boundary of a medium, some of the wave boundary of a medium, some of the wave energy continues into new medium (transmitted energy continues into new medium (transmitted wave) and some of the wave energy is wave) and some of the wave energy is reflected back (reflected wave)reflected back (reflected wave)
The wave that continues on (transmitted wave) The wave that continues on (transmitted wave) will have the same frequency as the original will have the same frequency as the original wave (incident wave)wave (incident wave)
Wave Behaviour in Different Wave Behaviour in Different MediaMedia
If the difference in media is small:If the difference in media is small:– Amplitude of transmitted wave almost = incident Amplitude of transmitted wave almost = incident
wavewave– Amplitude of reflected wave = smallAmplitude of reflected wave = small– This means most energy is transmitted to new This means most energy is transmitted to new
mediummedium If the difference in media is large:If the difference in media is large:
– Most of wave energy will be reflectedMost of wave energy will be reflected– As a result, amplitude of the reflected wave will As a result, amplitude of the reflected wave will
almost = amplitude of the incident wavealmost = amplitude of the incident wave
Wave Behaviour in Different Wave Behaviour in Different MediaMedia
When wave passes from a less dense to a When wave passes from a less dense to a more dense medium (i.e. Slinky wave hitting more dense medium (i.e. Slinky wave hitting a wall)a wall)– The reflected wave will be invertedThe reflected wave will be inverted
When a wave passes from a more dense When a wave passes from a more dense media to a less dense medium (i.e. Slinky media to a less dense medium (i.e. Slinky wave to air)wave to air)– The reflected wave will be erectThe reflected wave will be erect
Waves Speeds in Different MediaWaves Speeds in Different Media
Wave from a light spring moving to a heavy Wave from a light spring moving to a heavy spring:spring:– Frequency of waves are the same (remember Frequency of waves are the same (remember
frequency only depends on the source frequency only depends on the source producing the wave)producing the wave)
– Speed of the wave in the heavier spring is Speed of the wave in the heavier spring is slowerslower
– Using our equation (velocity = frequency x Using our equation (velocity = frequency x wavelength), less speed = smaller wavelengthwavelength), less speed = smaller wavelength
– If speed of wave increases in the new medium, If speed of wave increases in the new medium, wavelength will be largerwavelength will be larger
Standing WavesStanding Waves When two pulses with equal, but opposite amplitude When two pulses with equal, but opposite amplitude
meet, one point in the medium will remain meet, one point in the medium will remain completely undisturbedcompletely undisturbed– This point is called a This point is called a nodenode– At a node, the medium is never displacedAt a node, the medium is never displaced– It is produced by It is produced by destructive interferencedestructive interference
When two pulses with equal amplitude in the same When two pulses with equal amplitude in the same direction meet, one point in the medium undergoes direction meet, one point in the medium undergoes the greatest displacementthe greatest displacement– This point is called an This point is called an antinodeantinode– At an antinode, the medium has the greatest At an antinode, the medium has the greatest
displacmentdisplacment– It is produced by It is produced by constructive interferenceconstructive interference
Standing WavesStanding Waves
Standing waves Standing waves are produced by are produced by identical waves identical waves travelling in opposite travelling in opposite directionsdirections
The wave appears The wave appears to be standing stillto be standing still
It has both nodes It has both nodes and antinodesand antinodes
Complete Wave Ripple Tank LabComplete Wave Ripple Tank Lab
http://phet.colorado.edu/en/simulation/wave-interference
Wave ReflectionWave Reflection
Law of Reflection:Law of Reflection:The angle of incidence is equal to the angle The angle of incidence is equal to the angle of reflectionof reflection
Wave RefractionWave Refraction
Refraction = what happens when waves move from Refraction = what happens when waves move from one medium to another (i.e. From shallow to deep one medium to another (i.e. From shallow to deep water)water)– Shallow waves have shorter wavelength (since Shallow waves have shorter wavelength (since
frequency stays the same, velocity must decrease)frequency stays the same, velocity must decrease) When waves enter different media, the direction of When waves enter different media, the direction of
the wave can change. This is known as refraction.the wave can change. This is known as refraction.
Wave DiffractionWave Diffraction
When waves pass When waves pass through small barrier, through small barrier, they bend around they bend around edges forming edges forming circular wavescircular waves
Spreading of waves Spreading of waves around the edge of a around the edge of a barrier is called barrier is called diffractiondiffraction
Wave InterferenceWave Interference
When two waves pass When two waves pass through a barrier, both are through a barrier, both are diffracted (become circular diffracted (become circular waves) PLUS the two waves waves) PLUS the two waves interfere with eachotherinterfere with eachother
Interference produces Interference produces regions of constructive and regions of constructive and destructive interferencedestructive interference– Constructive = two crests or Constructive = two crests or
two troughs meettwo troughs meet– Destructive = a crest meets a Destructive = a crest meets a
troughtrough
Water InterferenceWater Interference
Constructive Constructive interference creates interference creates antinodes while antinodes while destructive interference destructive interference creates nodescreates nodes
This pattern produces This pattern produces “antinodal lines”“antinodal lines”
Between antinodal lines Between antinodal lines are areas when crests are areas when crests meet troughs – these meet troughs – these are are nodal linesnodal lines