Unit 11:Unit 11:

Characteristics of Characteristics of WavesWaves

Waves

Waves are rhythmic disturbances that carry energy through matter or spaceA wave is the result of energy moving from one

place to another ( via Kinetic energy)When a wave moves through matter, the

particles of the matter do NOT move, ONLY the wave moves

Medium

material through which a wave transfers energysolid, liquid, gas, or combinationCertain waves do not need a medium but must

be transmitted through a vacuum ( ex light)

electromagnetic waves don’t need a medium (e.g. visible light)

Medium

A medium transfers wave energy but has no overall motion itself

As the wave moves pastThe object, the object bobs Up and downThe wave moves forward andThe object stays in the same PlaceReason: Energy is transmitted, but matter is not

2 Properties of medium affect wave speed

1. Density of medium: waves move slower in denser medium ( has

more inertia)

2. Elasticity: The ability of a medium to return to its original

shape after being disturbedWaves move faster in more elastic medium

Waves

Two Types:

Longitudinal Transverse

Ex clap hands Ex Ocean wave

Types of Waves:Types of Waves: Transverse WavesTransverse Waves: waves that move the : waves that move the

medium at right angles to the direction in which medium at right angles to the direction in which the waves are traveling.the waves are traveling.

Longitudinal WavesLongitudinal Waves: move particles parallel to : move particles parallel to the direction the wave is moving, the direction the wave is moving, ““push-pullpush-pull” ” waves.waves.

Transverse Waves

Transverse Wavesmedium moves

perpendicular to the direction of wave motion (at a right angle to direction of wave)

Transverse Waves

Wave Anatomy

crests

troughswavelength

wavelength

amplitude

amplitude

corresponds to the amount of

energy carried by the wave

nodes

Properties of a wave

Crest: high point of waveTrough: low point of wavAmplitude: ½ distance from crest to troughWavelength: distance between 2 consecutive

crests or troughsPeriod: time for one wave to pass a given spot

Properties of WavesProperties of Waves

AmplitudeAmplitude –– in a transverse wave in a transverse wave – – the height away from the the height away from the ““restrest” ” position. The amplitude in a position. The amplitude in a longitudinal wave is the measure of longitudinal wave is the measure of how compressed or rarefied the how compressed or rarefied the medium becomes.medium becomes.

WavelengthWavelength – – the distance between the distance between two corresponding parts of a wave.two corresponding parts of a wave.

Properties of WavesProperties of Waves

FrequencyFrequency – – the number of the number of complete waves that pass a given complete waves that pass a given point in a certain period of time.point in a certain period of time.

Frequency is measured in Frequency is measured in HERTZHERTZ, , one one HzHz is a wave that occurs once is a wave that occurs once

every second.every second.

Longitudinal Waves

Longitudinal Waves (a.k.a. compressional)medium moves in the same direction as wave motionMotion of medium is parallel to the directon of the wave

movement

Longitudinal Waves

Wave Anatomy

rarefaction

compression

wavelength

wavelength

Amount of compression corresponds to amount of energy AMPLITUDE.

Measuring Waves

Frequency ( f )

# of waves passing a point in 1 second

Hertz (Hz)shorter wavelength

higher frequency higher energy

1 second

Measuring Waves

Velocity ( v )speed of a wave as it moves forwarddepends on wave type and medium

v = × f v: velocity (m/s)

: wavelength (m)

f: frequency (Hz)

SpeedSpeed (meters/sec)= wavelength x frequency (meters/sec)= wavelength x frequency FrequencyFrequency (Hz = 1/sec)= speed / Wavelength (Hz = 1/sec)= speed / Wavelength WavelengthWavelength (meters) = speed / Frequency (meters) = speed / Frequency

Designated by Greek letter lambda - Designated by Greek letter lambda -

Speed Frequency & Speed Frequency & WavelengthWavelength

Speed

Wavelength x frequency

S

x f

S = x f = 1.5 m x 280 Hz = 420 m/s

= S / f = 5.0 m/s / 2.5 Hz = 2 m

WORK:v = × f

v = (3.2 m)(0.60 Hz)

v = 1.92 m/s

Measuring Waves

EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.

GIVEN:

v = ?

= 3.2 m

f = 0.60 Hz

v

f

WORK: f = v ÷

f = (5000 m/s) ÷ (417 m)

f = 12 Hz

Measuring Waves

EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?

GIVEN:

= 417 m

v = 5000 m/s

f = ?

v

f

Interactions of Waves

There are 4 types of wave interaction:

1.Reflection

2.Refraction

3.Diffraction

4.Interference

ReflectionReflection Bounce back waveBounce back wave

Angle of IncidenceAngle of Incidence is the angle of the is the angle of the wave coming into the object reflecting the wave coming into the object reflecting the wave.wave.

Angle of Reflection Angle of Reflection is the angle bouncing is the angle bouncing off and going away from the object.off and going away from the object.

Incident waveIncident wave: incoming : incoming wavewave

Reflective wave Reflective wave is the wave is the wave that bounces backthat bounces back

Law of reflectionLaw of reflection

RefractionRefraction

The bending of a wave due to the The bending of a wave due to the wave wave

moving from one type of medium moving from one type of medium into anotherinto another

– – – –

– – Wave passing a barrier or going Wave passing a barrier or going through a hole in a barrier bends and through a hole in a barrier bends and causes the wave to wrap around the causes the wave to wrap around the barrierbarrier

DiffractionDiffraction

when two or more waves meet, they interact. This when two or more waves meet, they interact. This interaction is called interference.interaction is called interference. 1. 1. Constructive Interference Constructive Interference –– the combining the combining

of waves to cause higher amplitude of any of of waves to cause higher amplitude of any of the original waves.the original waves.

InterferenceInterference – 2 types – 2 types

2. 2. Destructive Interference Destructive Interference – – when the combining of the waves when the combining of the waves produce a new wave with a smaller produce a new wave with a smaller amplitude than the beginning wavesamplitude than the beginning waves

InterferenceInterference –2 types –2 types

Standing WavesStanding Waves Standing Waves Standing Waves – – the combining of the the combining of the

incoming and reflected wave so that the incoming and reflected wave so that the resultant appears to be standing stillresultant appears to be standing still

NodeNode – – the point where Constructive the point where Constructive Interference and Destructive Interference Interference and Destructive Interference cause an amplitude of zero on the cause an amplitude of zero on the standing wave.standing wave.

Standing WavesStanding Waves AntinodeAntinode – – the point where Constructive the point where Constructive

Interference and Destructive Interference of Interference and Destructive Interference of a standing wave are represented by the crest a standing wave are represented by the crest and the trough.and the trough.

ResonanceResonance – – the point where vibrations the point where vibrations traveling thru and object matches the natural traveling thru and object matches the natural vibrations of an object. I.e. an opera singer vibrations of an object. I.e. an opera singer hitting a note and shattering a crystal glass.hitting a note and shattering a crystal glass.

Seismic WavesSeismic Waves Seismic Waves Seismic Waves – – waves caused by waves caused by

the release of energy due to the release of energy due to earthquakes composed of earthquakes composed of P - primary wavesP - primary waves S - secondary wavesS - secondary waves L - surface wavesL - surface waves

P WavesP Waves P waves P waves –- –- Primary waves are pPrimary waves are pressure ressure

waves & waves & are the fastest moving waves, are the fastest moving waves, they travel thru solids and liquids, Push-they travel thru solids and liquids, Push-Pull Waves AKA Longitudinal wavesPull Waves AKA Longitudinal waves

S WavesS Waves S Waves S Waves – – Secondary Waves are slower Secondary Waves are slower

than primary waves, they cannot travel than primary waves, they cannot travel thru liquid and are Transverse Waves.thru liquid and are Transverse Waves.

L WavesL Waves L Waves (last waves) Surface wave L Waves (last waves) Surface wave – – the the

combination on the Earthcombination on the Earth’’s surface of Primary s surface of Primary and Secondary waves. and Secondary waves. The rolling chaotic movement of the surfaceThe rolling chaotic movement of the surface Cause the most damage of the seismic wavesCause the most damage of the seismic waves

Sound waves

Sound is a form of energy that causes Molecules of a medium to vibrate back and forth

Materials that are elastic transmit soundSound waves are longitudinal waves

Speed of Sound

344 m/s in air at 20°CDepends on 2 conditions :

1. Type of medium

• travels better through liquids and solids

• can’t travel through a vacuum

2. Temperature of medium

• travels faster at higher temps

Human Hearing

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea

Human Hearing

Pitchhighness or

lowness of a sound

depends on frequency of sound wave

human range: 20 - 20,000 Hz

ultrasonic waves

subsonic waves

Human Hearing

Intensityvolume of sounddepends on energy (amplitude) of sound

wavemeasured in decibels (dB)

Human Hearing

7080

100110

120

40

1810

0

DECIBEL SCALE

Doppler Effect

Doppler Effectchange in wave frequency

caused by a moving wave source

moving toward you - pitch sounds higher

moving away from you - pitch sounds lower

Doppler Effect

Stationary source Moving source Supersonic source

same frequency in all directions

waves combine to produce a shock wave

called a sonic boom

higher frequency

lower frequency

Doppler Rader

Is an instrument used to measure the velocity and direction of a moving object.

Was invented in 1904 by Christian Hulsmer, while detecting a distant ship in a foggy climate.

2 types of Doppler radar:

1.Police radar gun

2.Weather doppler

1. Police Radar gun

sends a beam of electromagnetic radiation waves, tuned to a precise frequency at a moving object, allows for speed calculations

2. Weather Doppler Radar: How it works

Doppler radars detect rainfall by sending out radio waves from an antenna, which are reflected back to the transmitter

The frequency of the reflected radio waves depends on whether the object (rain) is moving away from the antenna ( lower frequency) or the object is moving toward the antenna ( higher frequency)

The location of the objects are calculated by determining the time required for the waves to bounce back in the transmitter allowing weather prediction

Sonar

A sound navigation and ranging system that uses high frequency ultra sonic waves

The distance of the object is calculated by multiplying the speed of a sound wave in water by ½ the time it takes the wave to make the round trip

Echolocation

also called bio sonar, is the biological sonar used by several kinds of animals

Seeing with Sound

Ultrasonic waves - above 20,000 Hz

Medical Imaging SONAR“Sound Navigation Ranging”

Music vs. Noise

Musicspecific pitches and sound qualityregular pattern

Noiseno definite pitchno set pattern

Resonance

Resonancespecial case of forced

vibrationobject is induced to

vibrate at its natural frequency

Resonance

“Galloping Gertie”The Tacoma Narrows Bridge Disaster

Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.

Resonance

Forced Vibrationwhen one vibrating object

forces another object to vibrate at the same frequency

results in a louder sound because a greater surface area is vibrating

used in guitars, pianos, etc.

Pitch: how high or low the sound is

II. The Nature of Sound Speed of Sound Human hearing Doppler effect Seeing with sound

Vibration = 1 compression and 1 rarefaction

Harmonics

Fundamentalthe lowest natural frequency of an object

Overtonesmultiples of the fundamental frequency

Constructive - louder

Interference

Interferencethe ability of 2 or more waves to combine to

form a new wave

Destructive - softer

Interference

Beatsvariations in sound

intensity produced by 2 slightly different frequencies

both constructive and destructive interference occur

Acoustics

Acousticsthe study of sound

Reverberation echo effect produced

by the reflection of sound

Anechoic chamber - designed to eliminate reverberation.

EM Radiation

Electromagnetic Radiationtransverse waves produced by the motion of electrically

charged particlesdoes not require a mediumspeed in a vacuum = 300,000 km/selectric and magnetic

components are perpendicular

EM Radiation

Photonstiny, particle-like bundles

of radiationabsorbed and released

by electronsenergy increases with

wave frequency

EM Spectrum

long

low f

low energ

y

short

high f

high energy

Types of EM Radiation

1. Visible Light

small part of the spectrum we can see

ROY G. BIV - colors in order of increasing energy R O Y G. B I V

red orange yellow green blue indigo violet

Visible LightVisible Light White light is a mixture of the entire visible light White light is a mixture of the entire visible light

spectrumspectrum

2. Radiowaves

Radiowaves

lowest energy EM radiation and longest wavelength

1. Radiowaves

FM - frequency modulation AM - amplitude modulation)

3. Microwaves

Used to penetrate food and vibrate water & fat molecules to produce thermal energy

Highest frequency

Also used in cell phones

4. Infrared Radiation (IR)

slightly lower energy than visible light (can’t be seen)

can raise the thermal energy of objects

thermogram - image made by detecting IR radiation

5. Ultraviolet Radiation (UV)

slightly higher energy than visible lightTypes:

• UVA - tanning, wrinkles

• UVB - sunburn, cancer

• UVC - most harmful, sterilization

Ultraviolet Radiation (UV)Ozone layer depletion = UV exposure!

6. X rays

higher energy than UVcan penetrate soft tissue,

but not bonesDiscovered in 1896 by

Wilhelm Rontgen

7. Gamma rays

highest energy EM radiation

emitted by radioactive atoms

used to kill cancerous cells

Radiation treatment using radioactive cobalt-60.

EMS wavesEMS waves Long wavelength : Low Frequency & Low EnergyLong wavelength : Low Frequency & Low Energy Short wavelength : High Frequency & High Energy Short wavelength : High Frequency & High Energy

Light

Light and Color

Light and Matter Seeing Colors Mixing Colors

Reflection & MirrorsReflection & MirrorsWhen light strikes

an object It is either

reflected, absorbed or transmitted. .

A. Light and Matter

Opaqueabsorbs or reflects all light

Transparentallows light to pass through completely ex

glass

Translucentallows some light to pass through but can not

see image ex wax paper or frosted glass

Kinds of ReflectionsKinds of Reflections You see objects because light is reflected, bounced off of it. Law of Reflection: Angle of incidence equals the angle of

reflection– Angle coming in = angle going off

Regular Reflection: reflection off smooth surface – a mirror Diffuse Reflection: Irregular or bumpy, uneven surface –

wall

Real or Virtual?Real or Virtual? Image: a copy of an object formed by reflected or refracted light Virtual image: right side up appears to be coming from behind the

mirror. Real Image: is formed when reflected light rays actually meet at a

point. The image is upside down (inverted),

3 Types of Mirrors3 Types of Mirrors Plane Mirror: a flat mirror – produces an image that is right side (virtual) up and the

same size as the original object – Concave Mirror: a mirror with a surface curved inward like a “cave” or a bowl.

Light reflected comes together to meet at a Focal Point. Can produce virtual or real images

Convex Mirrors: A mirror w/ a curved surface facing outward Reflected rays appear to come from a focal point behind the mirror Images formed are always Virtual

Concave mirror Convex mirror

Plane mirror

Lens – Concave & ConvexLens – Concave & Convex Lenses – a curved piece

of material used to bend light

Concave lensesConcave lenses: as light passes through, they are bent away from the center

• Images produced are only virtual, not real

Convex lensesConvex lenses: cause light passing through to bend toward the focal point.

• The images produced depends on the position of the object

Concave Lens

Convex Lens

Seeing Colors

White lightcontains all visible colors - ROY G. BIV

In white light, an object…reflects the color you seeabsorbs all other colors

REFLECTSALL COLORS

ABSORBSALL COLORS

ColorColor The color of the object you see is the light that is

reflected from its surface. All other colors are absorbed by the object.

Vision - StructureVision - StructureNeed to know these structures & Need to know these structures &

their function:their function: CorneaCornea: begins to focus : begins to focus

lightlight Aqueous humorAqueous humor: fluid : fluid

between inside of cornea between inside of cornea & the outside of the lens& the outside of the lens

IrisIris: the color of the eye. A : the color of the eye. A muscle that opens & muscle that opens & closes to regulate pupil closes to regulate pupil sizesize

PupilPupil: hole through which : hole through which light passeslight passes

LensLens: flexible structure : flexible structure that focuses image on that focuses image on the retinathe retina

Vision - StructureVision - StructureNeed to know these structures & Need to know these structures &

their function:their function: Ciliary muscleCiliary muscle: ligaments : ligaments

attach the lens to these, they attach the lens to these, they contract & stretch the lens contract & stretch the lens allowing near & far focusallowing near & far focus

Vitreous humorVitreous humor: fluid inside : fluid inside eyeball maintains size & eyeball maintains size & shape of the eyeshape of the eye

RetinaRetina: contains the rods & : contains the rods & cones that are sensitive to cones that are sensitive to lightlight

Choroid coatChoroid coat: middle layer of : middle layer of the eyeballthe eyeball

ScleraSclera: the outer “whites of : the outer “whites of the eye”the eye”

Optic nerveOptic nerve: takes rod & : takes rod & cone impulse back to the cone impulse back to the occipital lobe for processingoccipital lobe for processing

Image Image ProcessingProcessing

FoveaFovea – – The central region where images focused is the fovea.

Rods Rods – about 1 billion, – about 1 billion, sensitive to brightness, sensitive to brightness, light and dark & light and dark & movementmovement

ConesCones – detect color, – detect color, about 3 million. 3 types about 3 million. 3 types of cones, sensitive to of cones, sensitive to red, blue & green red, blue & green wavelengths of light.wavelengths of light.

All rods & cones have All rods & cones have nerve fiber attached, nerve fiber attached, these collect at the back these collect at the back of the eye and form the of the eye and form the optic nerveoptic nerve which carries which carries the signal back to the the signal back to the eye.eye.

Seeing Colors

The retina contains…Rods - dim light, black & whiteCones - color

• red - absorb red & yellow

• green - absorb yellow & green

• blue - absorb blue & violet

Stimulates red & green cones

Stimulates all cones

Seeing Colors

Color Blindnessone or more sets of

cones does not function properly

Test for red-green color blindness.

Mixing Colors

Primary light colors

red, green, blue

additive colors

combine to form white light

View Java Applet on primary light colors.

EX: computer RGBs

C. Mixing Colors

Filtertransparent material

that absorbs all light colors except the filter color

View Java Applet on filters.

Mixing Colors

Pigmentcolored material that absorbs

and reflects different colors

Primary pigment colorscyan, magenta, yellowsubtractive colorscombine to form blackEX: color ink cartridges

C. Mixing Colors

Light Pigment

When mixing pigments, the color of the mixture is the color of light that both pigments reflect.

Light

Wave Properties of Light

ReflectionRefractionDiffraction Interference

Reflection

Reflectionwhen a wave

strikes an object and bounces off

incident beam reflected beam

Normal

Reflection

Law of Reflectionthe angle of

incidence equals the angle of reflection

Refraction

Refractionbending of waves when passing

from one medium to anothercaused by a change in speed

• slower (more dense) light bends toward the normal

SLOWER

FASTER

• faster (less dense) light bends away from the normal

Refraction

Refraction depends on…

speed of light in the medium

wavelength of the light - shorter wavelengths (blue)bend more

Refraction

Example:

View explanation.

Diffraction

Diffraction

bending of waves around a barrier

longer wavelengths (red) bend more - opposite of refraction

Interference

Interferenceconstructive brighter lightdestructive dimmer light

Cool Applications!

Fiber OpticsTotal Internal Reflection

• when all light is reflected back into the denser medium

Cool Applications!

The “Broken Pencil”refraction

View animation and explanation of the “Broken Pencil.”

Cool Applications!

Rainbowsrefraction-reflection-refraction

Prisms & RainbowsPrisms & Rainbows

PrismsPrisms: Separates white light into its component colors. The longer the wavelength, the less it will be bent by the prism.

RainbowsRainbows- light shining thru tiny droplets of water, each droplet acts as a prism

Cool Applications!

Diffraction Gratingsglass or plastic made up

of many tiny parallel slitsmay also be reflectivespectroscopes, reflective

rainbow stickers, CD surfaces

Cool Applications!

Thin Films - Bubbles & Oil Slicksinterference results from double reflection

Cool Applications!

Blue Sky & Red Sunsets

NOON• less atmosphere• less scattering• blue sky, yellow sun

SUNSET• more atmosphere• more scattering• orange-red sky & sun

• Molecules in atmosphere scatter light rays.

• Shorter wavelengths (blue, violet) are scattered more easily.