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