unit 11: characteristics of waves. waves waves are rhythmic disturbances that carry energy through...
TRANSCRIPT
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.