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Ch. 18 - Waves & Sound
I. Characteristics of Waves Waves Transverse waves Longitudinal waves Measuring waves
A. Waves
Wavesrhythmic disturbances that carry energy through
matter or space
Mediummaterial through which a wave transfers energysolid, liquid, gas, or combinationelectromagnetic waves don’t need a medium
(e.g. visible light)
B. Waves & Energy
Waves Carry energy Waves are caused by
vibrations Can do work Move objects
Energy Waves carry energy Vibration is a transfer
of energy As waves carry
energy the particles in the medium move
the direction of the motion determines the type of wave
C. Categories of Waves
Mechanical Waves Must travel through a
medium Cannot travel through a
vacuum Examples: sound, ocean
waves
Electromagnetic Waves
Does not require a medium Can be transferred through a
vacuum Examples: light, UV rays,
Visible light
D. Transverse Waves
Transverse Wavesmedium vibrates
perpendicular to the direction of wave motion
Examples: water waves, electromagnetic waves
B. Transverse Waves
Wave Anatomy
crests
troughs
wavelength
wavelength
amplitude
amplitude
corresponds to the amount of
energy carried by the wave
nodes
E. Longitudinal Waves
Longitudinal Waves (a.k.a. compressional waves)medium moves in the same direction as the wave’s
motionExamples: sound waves, springs, slinky
E. Longitudinal Waves
Wave Anatomy
rarefaction
compression
wavelength
wavelength
Amount of compression corresponds to amount of energy AMPLITUDE
F. Measuring Waves
Frequency ( f )
# of waves passing a point in 1 second
SI unit: Hertz (Hz)
shorter wavelength higher frequency higher energy
1 second
1
Frequency = period ( )
orperiod = the amount of time for one
cycle to do a complete motion
Frequency is measured in hertz (Hz).
1Hz = 1 wave per second
Cyclesecond
F. Measuring Waves
F. 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)
F. Measuring WavesSolid
Molecules are close together so waves travel very quickly.
Liquid Molecules are farther apart
but can slide past one another so waves do not travel as fast.
Gas
Molecules are very far apart so a molecule has to travel far before it hits another molecule, so waves travel slowest in gases.
WORK:v = × f
v = (3.2 m)(0.60 Hz)
v = 1.92 m/s
F. 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
F. 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
Ch. 17 – Waves
II. Wave Behavior Reflection Refraction Diffraction Interference Constructive Interference Destructive Interference Doppler effect
A. Wave Interactions
Wave InteractionWhen a wave meets an object or another
wave.When a wave passes into another mediumExamples: reflection, diffraction, refraction,
interference, resonance
A. Reflection
Reflectionwhen a wave
strikes an object and bounces off
incident beam reflected beam
Normal
B. 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
B. Refraction
Refraction depends on…
speed of light in the medium
wavelength of the light - shorter wavelengths (blue)bend more
C. Diffraction
The bending of a wave as it moves around an obstacle or passes through a narrow opening.
C. Diffraction
Diffraction
bending of waves around a barrier
longer wavelengths (red) bend more - opposite of refraction
E/F. Constructive & Destructive Interference
Both are caused by two or more waves interacting, but…
Constructive interference combines the energies of the two waves into a greater amplitude
Destructive interference reduces the energies of the two waves into a smaller amplitude.
G. Doppler Effect
A change in wave frequency caused by movement of sound source, motion of the listener, or both.
Ch. 18 - Waves & Sound
III. The Nature of Sound Speed of Sound Human hearing Doppler effect Seeing with sound
A. Speed of Sound
344 m/s in air at 20°CDepends on:
Type of medium• travels better through solids than through liquids
• can’t travel through a vacuumTemperature of medium
• travels faster at higher temperatures
B. Human Hearing
sound wave
vibrates ear drum
amplified by bones
converted to nerve impulses in cochlea
B. Human Hearing
Pitchhighness or
lowness of a sound
depends on frequency of sound wave
human range: 20 - 20,000 Hz
ultrasonic waves
subsonic waves
B. Human Hearing
Intensityvolume of sounddepends on energy (amplitude) of sound
wavemeasured in decibels (dB)
C. 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
C. 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
D. Seeing with Sound
Ultrasonic waves - above 20,000 Hz
Medical Imaging SONAR“Sound Navigation Ranging”
A. Electromagnetic 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
C. Types of EM Radiation
Radio wavesLowest energy EM radiationFM - frequency modulation AM - amplitude modulation
Microwavespenetrate food and vibrate
water & fat molecules to produce thermal energy
C. Types of EM Radiation
Infrared Radiation (IR)slightly lower energy than
visible lightcan raise the thermal energy
of objectsthermogram - image made by
detecting IR radiation
C. Types of EM Radiation
Visible Lightsmall 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
C. Types of EM Radiation
Ultraviolet Radiation (UV)slightly higher energy than visible lightTypes:
• UVA - tanning, wrinkles• UVB - sunburn, cancer• UVC - most harmful,
sterilization
C. Types of EM Radiation
Gamma rayshighest energy on
the EM spectrumemitted by
radioactive atomsused to kill
cancerous cells Radiation treatment using radioactive cobalt-60.
A. Light and Matter
Opaqueabsorbs or reflects all light
Transparentallows light to pass through completely
Translucentallows some light to pass through
B. 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
B. 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
B. Seeing Colors
Color Blindnessone or more sets of
cones does not function properly
Test for red-green color blindness.
C. 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.
C. 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.
Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.
Ch. 19 - Light
III. Wave Properties of Light(p.546-550)
ReflectionRefractionDiffraction Interference
A. Wave Interactions
Wave InteractionWhen a wave meets an object or another
wave.When a wave passes into another mediumExamples: reflection, diffraction, refraction,
interference, resonance
A. Reflection
Reflectionwhen a wave
strikes an object and bounces off
incident beam reflected beam
Normal
B. 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
B. Refraction
Refraction depends on…
speed of light in the medium
wavelength of the light - shorter wavelengths (blue)bend more
C. Diffraction
Diffraction
bending of waves around a barrier
longer wavelengths (red) bend more - opposite of refraction
E. Cool Applications!
Fiber OpticsTotal Internal Reflection
• when all light is reflected back into the denser medium
E. Cool Applications!
The “Broken Pencil”refraction
View animation and explanation of the “Broken Pencil.”
E. Cool Applications!
Diffraction Gratingsglass or plastic made up
of many tiny parallel slitsmay also be reflectivespectroscopes, reflective
rainbow stickers, CD surfaces