WAVES Komang Gde Suastika Physics Dept Palangka Raya University Email: suastika358@yahoo.com

WAVESWAVES

Komang Gde SuastikaKomang Gde Suastika Physics DeptPhysics Dept Palangka Raya UniversityPalangka Raya University Email: suastika358@yahoo.comEmail: suastika358@yahoo.com

What do you know?

About waves?

TujuanTujuan

1. By the end of this lesson you will be able to:1. By the end of this lesson you will be able to:

State that a State that a wave transfers energywave transfers energy..

2. Use the following terms correctly in context: 2. Use the following terms correctly in context: wave, wave, frequency, wavelength, speed, amplitude, frequency, wavelength, speed, amplitude, periodperiod..

3. State the difference between a 3. State the difference between a Mechanical WavesMechanical Waves

and a and a Electromagnetic waves (EM Waves)Electromagnetic waves (EM Waves), and give , and give an example of each.an example of each.

4. State the difference between a 4. State the difference between a longitudinallongitudinal wave wave

and a and a transversetransverse wave, and give an example of each. wave, and give an example of each.

Perhatikan Fenomena berikutPerhatikan Fenomena berikut

WAVESWAVESa disturbance that transfers energy

Waves transfer energy…Waves transfer energy…

Waves transfer energy…Waves transfer energy…

CHARACTERISTICS OF WAVESCHARACTERISTICS OF WAVES

Waves are described according Waves are described according to their to their

AmplitudeAmplitudemeasures DISPLACEMENTmeasures DISPLACEMENTsize of the disturbancesize of the disturbance

Wavelength Wavelength distance of a distance of a ““repeating unitrepeating unit””Also called a cycleAlso called a cycle

Velocity Velocity vv speed = how fast wave travelsspeed = how fast wave travels

AMPLITUDEAMPLITUDE

Distance between Distance between ““rest & crestrest & crest”” or or ““rest & troughrest & trough””

Gives indication of Gives indication of ““powerpower”” or or ““strengthstrength”” of wave of wave(magnitude of earthquake = (magnitude of earthquake = Richter scale)Richter scale)

Does not affect Does not affect

velocity of wavevelocity of wave

Determines loudness (sound) or brightness (EM wave)Determines loudness (sound) or brightness (EM wave)

WAVELENGTH WAVELENGTH Distance between any two Distance between any two

repeating points on a waverepeating points on a wave

crest-crest, crest-crest, trough-trough,trough-trough,expansion-expansion, expansion-expansion, compression-compressioncompression-compression

Determines what colorsDetermines what colorswe see; what notes we hear (pitch)we see; what notes we hear (pitch)

Shorter wavelengths have more Shorter wavelengths have more cycles per minute because they cycles per minute because they arenaren’’t as longt as long

VELOCITY VELOCITY vv the rate at which the the rate at which the

energy travelsenergy travels; ; speed & directionspeed & direction

Depends on mediumDepends on medium Mechanical waves travel Mechanical waves travel

faster through dense faster through dense mediumsmediums

EM Waves are faster EM Waves are faster through less dense through less dense mediumsmediums

Frequency Frequency ƒƒ

measured in measured in wavelengths/second or wavelengths/second or cycles/secondcycles/second

HertzHertz (Hz) = number of (Hz) = number of wavelengths in 1 secondwavelengths in 1 second

Frequency is related to Frequency is related to velocity:velocity: v v = = ƒ ƒ

How oftenHow often number of wavelengths that pass any point per secondnumber of wavelengths that pass any point per second

PERIOD TPERIOD T

How longHow longAmount of time for one wavelength to pass a pointAmount of time for one wavelength to pass a point

Related inversely to frequencyRelated inversely to frequency

11 == 11

TT ff

PeriodPeriod == 11

FrequencyFrequency

Properties of WavesProperties of Waves

What is meant by the axis of a wave?What is meant by the axis of a wave?The axis is the line runningthrough the middle of thewave pattern.

What is meant by the crest of the What is meant by the crest of the wave?wave?

The crest is the top part of the wave

……and the trough?and the trough?

The trough is the bottompart of the wave.

What is the amplitude of the wave?What is the amplitude of the wave?

The amplitude is thedistance from the axis tothe crest

or from axis to trough.

Definition of Wavelength?Definition of Wavelength?The wavelength is thedistance after which thewave pattern repeats itself– the distance between twoidentical points on the wave

Wavelength is given the symbol λ pronounced lambda.

FrequencyFrequency

The frequency of the wave is the number The frequency of the wave is the number of waves each second.of waves each second.

It is measured in hertz (Hz) which justIt is measured in hertz (Hz) which just means means ““per secondper second””. .

FrequencyFrequency

Calculate the frequency of each of theCalculate the frequency of each of the

following waves:following waves:

125 waves passing a point in 10 seconds.125 waves passing a point in 10 seconds. 16 waves passing a point in 24 seconds.16 waves passing a point in 24 seconds. 30 waves passing a point in 1 minute.30 waves passing a point in 1 minute.

Carries energy from one place to another Carries energy from one place to another Classified byClassified by what what they move through they move through

1.1. Mechanical WavesMechanical Wavesthe energy is transferred by vibrations of medium the energy is transferred by vibrations of medium (medium = matter)(medium = matter)ex/ ocean waves move through waterex/ ocean waves move through water

2.2. Electromagnetic waves (EM Waves)Electromagnetic waves (EM Waves)the energy moves through disturbances in the the energy moves through disturbances in the electromagnetic field.electromagnetic field.

WAVE STRUCTUREWAVE STRUCTURE

CREST (peak)AMPLITUDEresting to max peak

WAVELENGTH

TROUGH

MECHANICAL WAVESMECHANICAL WAVES

travel through & gradually lose energy to that medium

Examples:Examples: water, sound, rope, & water, sound, rope, &

spring wavesspring waves

Mechanical Media:Mechanical Media: water, air, rope, springwater, air, rope, spring

require a medium (the material through which the

disturbance is moving) to transmit energy

Making a pulse

MECHANICAL WAVESMECHANICAL WAVESClassified by how medium vibrates

Pulse = direction of energy transfer

Vibration = direction of vibration of medium relative to pulse

3 types: Longitudinal, transverse, surface

MECHANICAL WAVESMECHANICAL WAVESClassified by how medium vibrates

Longitudinal Waves:Vibration is in the same direction as

wave pulse (parallel to wave pulse)

Transverse Waves:Vibration is at 900 (right angles) to wave pulse

Surface Waves:Vibration is circular Ex/ Ocean waves; surface waves

TRANVERSE WAVESTRANVERSE WAVES

Sideways or up & downSideways or up & down Examples:Examples:

S-type earthquake wavesS-type earthquake waves Electromagnetic (EM) or Electromagnetic (EM) or

light waveslight waves

Vibration is perpendicular to the direction of the motion of the wave

LONGITUDINAL WAVESLONGITUDINAL WAVES

Back and forth (compression & rarefraction)Back and forth (compression & rarefraction)

Also called compression or pressure waveAlso called compression or pressure wave

Examples:Examples: P-type earthquake wavesP-type earthquake waves Sound wavesSound waves

Vibration is parallel to the direction of the motion of the wave

Rarefraction (expansion)

Compression

Waves describe the EarthWaves describe the Earth

S waves move through solids only!!!

P waves move through solids & liquidsP waves move through solids & liquids

Are these MECHANICAL WAVES????

YES!! Seismic waves need a medium (the earth!)

Penjalaran GelombangPenjalaran Gelombangdalam Satu Dimensidalam Satu Dimensi

Fungsi Gelombang :)( vtxfy

)( vtxfy

Menjalar ke kanan

Menjalar ke kiri

Cepat-rambat Gelombang (Kecepatan Fasa) : dt

dxv

Superposisi dan Interferensi Superposisi dan Interferensi GelombangGelombang

Gelombang Bunyi

Cepat-rambat Gelombang di dalam Cepat-rambat Gelombang di dalam DawaiDawai

F

v Tegangan dawai

Massa dawai persatuan panjang 2MLT F

1ML

1LT v

Refleksi dan Transmisi Gelombang

Rambatan gelombang dari medium kurang rapat ke medium yang lebih rapat

Rambatan gelombang dari medium lebih rapat ke medium yang kurang rapat

Harmoni GelombangHarmoni Gelombang

xAy

2

sin

A

vtxAy

2

sinUntuk Gelombang yangMenjalar ke kanan

Tv atau vT

Ttx

Ay

2sin

2k

T 2

tkxAy sin

vtxAy

2

sin

Tv

T

txAy

2sin

PERSAMAAN GELOMBANGPERSAMAAN GELOMBANG

x

x

f (x)t = 0

c t

f (x - ct)

Gelombang Sinusoidal Dalam Domain RuangGelombang Sinusoidal Dalam Domain Ruang

)2

(sin xAy

Amplitudo

x

A

Panjang gelombang

Bilangan gelombang

)(sin xkAy

x

Gelombang Sinusoidal Dalam Domain WaktuGelombang Sinusoidal Dalam Domain Waktu

)2

(sin tT

Ay

t

A

T

Perioda

Amplitudo

)(sin tAy )2(sin tfAy

Frekuensi sudut

Frekuensi

Dalam Domain Ruang Dan WaktuDalam Domain Ruang Dan Waktu

)(sin txkAy

Sebuah gelombang perpindahan dinyatakan dengan :  (x,t) = 0,02 sin [ 2 ( 0,5 x – 10 t ) ] mTentukan panjang gelombang, frekuensi dan kecepatannya.

Contoh

Jawab :

)22

(sin)(sin),( tfxAtxkAtx

)105,0(2sin02,0)1

(2sin),( txtfxAtx

TcT

f1

m2

Hzf 10

smfT

c /20)10)(2(

Tugas Tugas Persamaan suatu gelombang yang bergerak Persamaan suatu gelombang yang bergerak transversal transversal

3001.02sin2

xty

Dimana x dan y dalam cm dan t dalam detik. Berapa amplitudo, panjang gelombang, frekuensi dan kecepatan rambat gelombang itu