Ch 17 & 18 notesCh 17 & 18 notesWAVES & Electromagnetic WAVES & Electromagnetic

spectrumspectrum

What is a Wave?What is a Wave?

WavesWaves-rhythmic disturbances -rhythmic disturbances that carry energy through that carry energy through matter/spacematter/space

MediumMedium-material through -material through which a wave can travel & which a wave can travel & transfer energytransfer energy

– *solid, liquid, gas, or *solid, liquid, gas, or combinationcombination

3 major types of waves

1. compressional aka Longitudinal

2. Transverse3. Surface

Longitudinal Waves (Longitudinal Waves (aka compressional) -aka compressional) -matter vibrates in same direction as matter vibrates in same direction as

the wave Propagation (travels), parallelthe wave Propagation (travels), parallel

(compression or push-and-pull waves)(compression or push-and-pull waves)Ex: Ex: PPrimary earthquake waves & sound wavesrimary earthquake waves & sound waves

• CompressionCompression-area where -area where particles in a medium are particles in a medium are spaced close togetherspaced close together

• RarefactionRarefaction-area where -area where particles in a medium are particles in a medium are spread outspread out

Transverse Wave Transverse Wave -media move at -media move at right angle to direction of wave right angle to direction of wave propagationpropagation

WavelengthWavelength Crest Crest

AmplitudeAmplitude

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _rest point (equilibrium) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _rest point (equilibrium) _ _

AmplitudeAmplitude

TroughTrough

• CrestCrest-highest point of the -highest point of the wave above rest pointwave above rest point

• TroughTrough-lowest point -lowest point below rest pointbelow rest point

• Wavelength(Wavelength(λλ)) -distance -distance btw a point on one wave btw a point on one wave & same point on next & same point on next cycle of wave.cycle of wave.

AmplitudeAmplitude-max -max displacement of displacement of medium from its medium from its rest point, rest point, corresponds to corresponds to amount of amount of energy a wave energy a wave carries carries (more (more energy = energy = greater greater amplitude)amplitude)

•FrequencyFrequency-# of wavelengths -# of wavelengths that pass a fixed point each that pass a fixed point each second, measured in Hertz second, measured in Hertz (Hz) (Hz) (Increasing Frequency = (Increasing Frequency = wavelength decreases)wavelength decreases)

•PeriodPeriod-time it takes for 1 -time it takes for 1 wavelength to pass a point wavelength to pass a point (Increasing Frequency = (Increasing Frequency = period decreases)period decreases)

Surface WaveSurface Wave- - travels along travels along a surface a surface separating separating two media two media

Ex: Ocean Waves Ex: Ocean Waves

(btw water & (btw water & air)air)

Wave Movements

Wave speedWave speed

Velocity of wave=wavelength x Velocity of wave=wavelength x frequencyfrequency

V V ww = = (lambda) x f (lambda) x f

[m/s] = [m] x [Hz][m/s] = [m] x [Hz]

Wave velocity

wavelength

frequency

Wave SpeedWave Speed

One end of a rope is vibrated One end of a rope is vibrated to produce a wave with a to produce a wave with a wavelength of 0.25meters. wavelength of 0.25meters. The frequency of a wave is 3 The frequency of a wave is 3 hertz. What is the speed of hertz. What is the speed of the wave?the wave?

Wave SpeedWave Speed•Wavelength = 5mWavelength = 5m

•Frequency = 15HzFrequency = 15Hz

•Speed =?Speed =?

Star Questions

• Time it takes for one wavelength to pass a point

• Period

• Unit for frequency

• Hz

• Dense part of longitudinal wave

•compression

ReflectionReflection

Behavior of wavesBehavior of waves

1.1. Reflection Reflection – wave wave bouncesbounces off a surface off a surface

that it cannot pass throughthat it cannot pass through– does not change speed or does not change speed or

frequency, but wave can be frequency, but wave can be flipped upside down flipped upside down

– occurs with all types of waves

RefractionRefraction

RefractionRefraction– bendingbending of a wave as it of a wave as it

enters a new medium at enters a new medium at an anglean angle

– one side of the wave one side of the wave moves more slowly moves more slowly ((dependent on speeddependent on speed) ) than the other side, than the other side, *violet light bends most

DiffractionDiffraction– bending of wave as it bending of wave as it

moves moves around an around an obstacleobstacle or passes or passes through a narrow through a narrow openingopening

– diffracts more of its diffracts more of its wavelength is large wavelength is large compared to the size of compared to the size of an opening or obstacle an opening or obstacle

InterferenceInterference

– Two typesTwo types

1. 1. constructconstructiveive-the waves -the waves add add togethertogether

2. 2. destructdestructiveive-the waves -the waves subtractsubtract from each other from each other as they overlapas they overlap

Complete Constructive

Partial Constructive

Principle of superposition

Complete Destructive

Partial Destructive

Principle of superposition

Standing wave=that appears to stay in 1 place.

Node: no movement from rest positionAntinode: crest or troughs

Behavior of wavesBehavior of waves

PolarizationPolarization– Light w/ waves that vibrate in Light w/ waves that vibrate in

one plane is polarized lightone plane is polarized light– Horizontal filter blocks waves Horizontal filter blocks waves

vibrating on a vibrating on a verticalvertical plane plane– Vertical filter blocks waves Vertical filter blocks waves

vibrating on a vibrating on a horizontal horizontal planeplane

PolarizationPolarization

Sound (a longitudinal wave)Sound (a longitudinal wave)

Speed of sound depends on:Speed of sound depends on:

1.1. type of medium type of medium - solid - solid best conductorbest conductor

*no sound on moon or in *no sound on moon or in spacespace

2.2. temperature of mediumtemperature of medium -faster at higher temps-faster at higher temps

SoundSound

•Intensity – rate at which a wave’s energy flows through a given area

•Loudness – human perception, measured in decibels (dB)

FYI!• Prolonged exposure

to any noise above 85 decibels (dB) can cause gradual hearing loss.

• 100 decibels - no more than 15 minutes prolonged exposure recommended

• 110 decibels - regular exposure of more than one minute risks permanent hearing loss without hearing protection.

SoundSound

Pitch Pitch – highness or lowness of – highness or lowness of a sounda sound

• high frequency = high pitchhigh frequency = high pitch• low frequency = low pitchlow frequency = low pitch• humans hear between 20 & humans hear between 20 &

20,000 Hz20,000 Hz• UltrasonicUltrasonic is above 20,000 is above 20,000

HzHz• InfrasonicInfrasonic (subsonic) is (subsonic) is

below (thunder)below (thunder)

SoundSound• ResonanceResonance – if the sound that – if the sound that

reaches an object is at the same reaches an object is at the same frequency of the object, the frequency of the object, the object will begin to vibrate at object will begin to vibrate at that frequencythat frequency

• Noise pollutionNoise pollution – includes – includes sounds that are loud, annoying sounds that are loud, annoying or harmful to the earor harmful to the ear

Why do concert places usually Why do concert places usually have carpet on walls and have carpet on walls and floors?floors?

Doppler effectDoppler effect

• change in sound frequency caused change in sound frequency caused by motion of the sound source, by motion of the sound source, motion of the listener, or bothmotion of the listener, or both

• Higher pitch, higher frequency as Higher pitch, higher frequency as object approachesobject approaches

• Lower pitch, lower frequency as Lower pitch, lower frequency as sound source moves awaysound source moves away

STAR Questions• What kind of wave is this?

– Transverse

• What state of matter is the best conductor?– Solid

• What 2 things affect the speed of sound?– Type of medium and temperature

• What type of wave is a sound wave?– Longitudinal (AKA compressional)

• Why is there no sound in space?– There is no medium for the sound waves

• Loudness is human perception of what wave property?– Intensity Amplitude Energy

• What wave property affects sound’s pitch?– frequency

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LIGHT WAVES

Electromagnetic radiation

•Transverse waves

•Do not need a medium

Radio Waves

•a) low frequency

•b) long wavelength

Infrared (IR)

• sunlight

• Heat• Body

gives off IR

Visible Light• only part

of the spectrum you can see

• ROYGBIV

LIGHT AND COLOR•In order for you to see an object,

it must reflect at least a little bit

of light

Ultraviolet• overexposure

can damage skin cells

– Causes skin cancer

• ozone layer protects us from most UV

X-Rays• can travel through

skin & muscle

• absorbed by denser materials such as bone

• used for taking pictures of bones

Gamma Rays

• highest frequency, shortest

• can be used to kill cancerous cells

Light Transmission• Opaque

Materials-absorb or reflect all light & you cannot see objects through them

Light Transmission•Transparent Materials-allow light to pass through & you can clearly see objects through them

•Translucent Materials-allow light to pass through but you cannot clearly see objects through them

Light Transmission

Star Questions

• Tell me in order the colors of the visible spectrum from longest to

shortest wavelength• ROYGBIV

•Type of em with highest frequency• Gamma

• Type of em with the longest wavelength

• Radio