Wave NotesWave Notes

• Identify a cycle of harmonic motionIdentify a cycle of harmonic motion• Relate pitch of a sound to its frequency and speedRelate pitch of a sound to its frequency and speed• Describe what happens to air when sound moves Describe what happens to air when sound moves

throughthrough• Describe factors that affect the speed of soundDescribe factors that affect the speed of sound• Explain the Doppler EffectExplain the Doppler Effect• Give examples of forced vibrationsGive examples of forced vibrations• Describe the conditions for resonanceDescribe the conditions for resonance• Identify the different kinds of electromagnetic Identify the different kinds of electromagnetic

waveswaves• Describe & Identify the four types of wave Describe & Identify the four types of wave

interactionsinteractions• Explain constructive & destructive interferenceExplain constructive & destructive interference

Chapter 13Chapter 13

Waves & SoundWaves & Sound

Harmonic MotionHarmonic Motion

Harmonic motionHarmonic motion – – motion that motion that repeatsrepeats

• Occurs in Occurs in cyclescycles – a unit of – a unit of motion that motion that repeats over and repeats over and overover

Harmonic MotionHarmonic Motion

OscillationOscillation – motion that – motion that repeats regularlyrepeats regularly

• A system with harmonic motion A system with harmonic motion is referred to as anis referred to as an oscillatoroscillator..

WavesWaves

WaveWave• a disturbance or vibration a disturbance or vibration that transfers energy through that transfers energy through matter or space.matter or space.

• OR an oscillation that OR an oscillation that travels!travels!

Ex: light, sound, earthquake, Ex: light, sound, earthquake, ocean wave…ocean wave…

SOUND & LIGHT WavesSOUND & LIGHT Waves

• Both vibrations/oscillationsBoth vibrations/oscillationsSoundSound- waves require a medium - waves require a medium (solid,liquid,gas) in which to (solid,liquid,gas) in which to travel .travel .

NO Medium = NO soundNO Medium = NO soundLightLight – Waves can pass through many – Waves can pass through many materials. Doesn’t require a materials. Doesn’t require a medium Can travel through space. medium Can travel through space. PURE Energy! PURE Energy!

(electromagnetic waves)(electromagnetic waves)

Tidbits about light…Tidbits about light…

• Produced by vibrating Produced by vibrating electrons in atoms.electrons in atoms.

• Carries energy and powerCarries energy and power• IntensityIntensity is analogous to is analogous to amplitude & describes energy amplitude & describes energy per second carried by a light per second carried by a light wave.wave.

• c (speed of light) 3 x 10c (speed of light) 3 x 1088 m/s m/s

Electromagnetic Electromagnetic SpectrumSpectrum

• Oscillations of electric Oscillations of electric particles or magnets create particles or magnets create electromagnetic waves electromagnetic waves (light).(light).

• Range of all frequencies of Range of all frequencies of electromagnetic waves is electromagnetic waves is referred to as the referred to as the spectrumspectrum..

Electromagnetic Electromagnetic Spectrum (see handout)Spectrum (see handout)

Wave InteractionsWave Interactions

• Reflection – wave bounces and goes Reflection – wave bounces and goes in a new direction.in a new direction.

• Refraction – the wave bends as it Refraction – the wave bends as it passes into and through the passes into and through the object.object.

• Diffraction – The wave bends Diffraction – The wave bends around an object or through holes around an object or through holes in the object.in the object.

• Absorption – The wave is absorbed Absorption – The wave is absorbed and disappears.and disappears.

The Law of ReflectionThe Law of Reflection

Incident angle = iIncident angle = i

Reflected angle = rReflected angle = r

Law: When a wave is Law: When a wave is reflected, The reflected, The angle of angle of incidence (i) = incidence (i) = the angle of the angle of reflection (r).reflection (r).

RefractionRefraction

Index of RefractionIndex of Refraction

• Light travels differently through Light travels differently through different mediums (s, l, g)different mediums (s, l, g)

• If light travels through one If light travels through one medium into another it bends, or medium into another it bends, or refractsrefracts

• Index of RefractionIndex of Refraction – describes a – describes a materials ability to bend light.materials ability to bend light.

Index of RefractionIndex of Refraction

• Varies slightly for a Varies slightly for a material depending on color material depending on color of light.of light.

• Glass/Prism will refract Glass/Prism will refract white light, separating it white light, separating it into a rainbowinto a rainbow

• Water has similar propertiesWater has similar properties

Refraction of LightRefraction of Light

• Continuously absorbed & re-Continuously absorbed & re-emitted by atoms.emitted by atoms.

• Moves at c Moves at c betweenbetween atoms only! atoms only!• Frequency does not change, but Frequency does not change, but wavelength does.wavelength does.

• Change in wavelength is Change in wavelength is proportional to how speed proportional to how speed changes.changes.

Diffraction

• Light will diffract... Light will diffract... – Shine a flashlight on a wall Shine a flashlight on a wall through a slot in a piece of through a slot in a piece of paper.paper.

– As you decrease the size of the As you decrease the size of the slot the light on the wall seems slot the light on the wall seems to “spread out”.to “spread out”.

– The diffraction occurs because the The diffraction occurs because the size of the slot is not much wider size of the slot is not much wider than the wavelength of the wave.than the wavelength of the wave.

Sound WavesSound Waves

• Waves can only travel through Waves can only travel through solids, liquids, and gases.solids, liquids, and gases.

Fastest to slowest : solid, liquid, gasFastest to slowest : solid, liquid, gasClose molecular connection = faster Close molecular connection = faster transmissiontransmission

NO SOUND IN A VACUUMNO SOUND IN A VACUUM(outer space): NO MATTER (outer space): NO MATTER for vibrations to travel.for vibrations to travel.

Pitch- how low or high Pitch- how low or high a sound seems a sound seems

• Freq & pitch Freq & pitch directly relateddirectly related

• Freq: 20-20,000 HzFreq: 20-20,000 Hz pitch = pitch = freq. freq. pitch = pitch = freq freq

Infrasonic < 20 HzInfrasonic < 20 Hz

ultrasonic > 20,000 ultrasonic > 20,000 HzHz

Dogs -hear ultrasonic frequencies.Dogs -hear ultrasonic frequencies.Elephants – hear infrasonic freq.Elephants – hear infrasonic freq.

Sound Waves SimulationSound Waves Simulation

Loudness – how intense Loudness – how intense a sound isa sound is

• Measured in DecibelsMeasured in Decibels• Determined by amplitude Determined by amplitude (amount of energy)(amount of energy)

• Most sounds fall between 0-Most sounds fall between 0-100 dB.100 dB.

• 0 dB quietest sound & 110 dB 0 dB quietest sound & 110 dB front row at a rock concertfront row at a rock concert

• Acoustics-Acoustics- Study of sound Study of sound

Speed of SoundSpeed of Sound

Depends on wind, humidity,temp.Depends on wind, humidity,temp.

0° C = 330 m/s0° C = 330 m/s

20 ° C = 340 m/s 20 ° C = 340 m/s • Warmer = faster!Warmer = faster!• HUMID = FASTERHUMID = FASTER

Sound waves travel slower Sound waves travel slower than light waves than light waves

What is the approximate What is the approximate distance of a thunderstorm distance of a thunderstorm when you note a 3 s delay when you note a 3 s delay between the flash of between the flash of lightning & sound of thunder? lightning & sound of thunder? (about 20 ° C )(about 20 ° C )

(340m/s ) (3)= 1020m(340m/s ) (3)= 1020m

Speed of SoundSpeed of Sound

• SubsonicSubsonic – speed slower than that – speed slower than that of sound.of sound.

• SupersonicSupersonic – speed faster than – speed faster than that of sound.that of sound.

• Supersonic jets “squish” sound Supersonic jets “squish” sound waves that are created as travels waves that are created as travels through the air… forming a through the air… forming a shock shock wavewave cone and a cone and a sonicsonic boomboom

Sonic boomSonic boom

13.10 The Doppler 13.10 The Doppler EffectEffect

The change in frequency of wave The change in frequency of wave motion resulting from motion resulting from motionmotion of of the sender or receiver.the sender or receiver.

Sender or receiver is moving!Sender or receiver is moving!

EX: Siren on police carEX: Siren on police car

As approaches-high pitchAs approaches-high pitch

As moves away- low pitchAs moves away- low pitch

Sound Wave Sound Wave InteractionsInteractions

• Sound waves can Sound waves can – Reflect (hard surfaces)Reflect (hard surfaces)– Refract (through materials)Refract (through materials)– Diffract (through small Diffract (through small openings)openings)

– Be absorbed (carpet & soft mats)Be absorbed (carpet & soft mats)• ReverberationsReverberations - multiple - multiple reflections of sound & can reflections of sound & can become “garbled”.become “garbled”.

13.7 Forced Vibrations 13.7 Forced Vibrations & natural frequency& natural frequency

An object forced An object forced to vibrate due to vibrate due to contact w/ a to contact w/ a wave from wave from another another vibrating vibrating object.object.

Ex: tuning forkEx: tuning fork

Natural frequencyNatural frequency- the frequency at - the frequency at which the least amount of energy which the least amount of energy is required to produce vibrations.is required to produce vibrations.

• all objects have a natural all objects have a natural frequency or set of frequencies at frequency or set of frequencies at which they vibrate when struck.which they vibrate when struck.

• Depends on : Elasticity & shape of Depends on : Elasticity & shape of objectobject

Tacoma BridgeTacoma Bridge

• http://fragg.me/video/tacoma-bridge

13.8 Resonance13.8 Resonance

Resounding or “sounding again”.Resounding or “sounding again”.

• Result of forced vibrations in an Result of forced vibrations in an object when the applied frequency object when the applied frequency matches the natural frequency of matches the natural frequency of the objectthe object

EX: tuning forksEX: tuning forks

13.9 13.9 InterferenceInterference – when 2 – when 2 waves overlapwaves overlap

2 types2 types

1.1.Constructive interferenceConstructive interference- - waves add together. Crests waves add together. Crests and troughs fall at same and troughs fall at same places. places.

• New wave has grater amplitude New wave has grater amplitude

See P. 222See P. 222

Destructive interferenceDestructive interference- Crest - Crest of one wave overlaps w/ of one wave overlaps w/ trough of another. trough of another.

Individual effects reduced.Individual effects reduced.

See P. 222 Figure 13.20See P. 222 Figure 13.20

BeatsBeats- Periodic loudness in - Periodic loudness in sound due to wave sound due to wave interference.interference.