Ch. 18 - Waves & Sound
I. Characteristics of Waves
 Waves
 Transverse waves
 Longitudinal waves
 Measuring waves
A. Waves
Waves
 rhythmic disturbances that carry energy through
matter or space
Medium
 material through which a wave transfers energy
 solid, liquid, gas, or combination
 electromagnetic 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. Types of Waves
Two Types:
Longitudinal
Transverse
D. Transverse Waves
Transverse Waves
medium vibrates
perpendicular to the
direction of wave
motion
 Examples: water waves,
electromagnetic waves
B. Transverse Waves
Wave Anatomy
corresponds to
the amount of
energy carried by
the wave
crests
wavelength
amplitude
amplitude
nodes
wavelength
troughs
E. Longitudinal Waves
Longitudinal Waves (a.k.a. compressional
waves)
medium moves in the same direction as the
wave’s motion
Examples: sound waves, springs, slinky
E. Longitudinal Waves
Wave Anatomy
compression
rarefaction
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
F. Measuring Waves
1
Cycle
Frequency = period ( second
)
or
period = the amount of time for one
cycle to do a complete motion
Frequency is measured in hertz (Hz).
1Hz = 1 wave per second
F. Measuring Waves
Velocity ( v )
speed of a wave as it moves forward
depends on wave type and medium
v=×f
v:
velocity (m/s)
:
wavelength (m)
f:
frequency (Hz)
F. Measuring Waves
Solid
 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.
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.
WORK:
v=×f
GIVEN:
v=?
 = 3.2 m
f = 0.60 Hz
v = (3.2 m)(0.60 Hz)
v

v = 1.92 m/s
f
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?
WORK:
f=v÷
GIVEN:
 = 417 m
v = 5000 m/s
f=?
v

f = (5000 m/s) ÷ (417 m)
f = 12 Hz
f
Ch. 17 – Waves
II. Wave Behavior






Reflection
Refraction
Diffraction
Interference
Constructive Interference
Destructive Interference
 Doppler effect
A. Wave Interactions
Wave Interaction
When a wave meets an object or another
wave.
When a wave passes into another medium
Examples: reflection, diffraction, refraction,
interference, resonance
A. Reflection
Normal
Reflection
when a wave
strikes an object
and bounces off
incident beam
reflected beam
A. Reflection
When a wave
bounces off a
surface that is
cannot pass through
B. Refraction
Refraction
bending of waves when passing
from one medium to another
caused by a change in speed
• slower (more dense)  light
bends toward the normal
• faster (less dense)  light
bends away from the normal
SLOWER
FASTER
B. Refraction
The bending of a
wave as it enters a
new medium at an
angle.
B. Refraction
Refraction depends on…
speed of light in
the medium
wavelength of
the light - shorter
wavelengths (blue)
bend more
B. Refraction
Example:
View explanation.
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
D. Interference
The interaction of
two or more waves
that combine in a
region of overlap
D. Interference
Two types of Interference
constructive  brighter light
destructive  dimmer light
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°C
Depends on:
Type of medium
• travels better through solids than through
liquids
• can’t travel through a vacuum
Temperature 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
Pitch
highness or
lowness of a
sound
depends on
frequency of
sound wave
human range:
20 - 20,000 Hz
ultrasonic waves
subsonic waves
B. Human Hearing
Intensity
volume of sound
depends on energy (amplitude) of sound
wave
measured in decibels (dB)
B. Human Hearing
DECIBEL SCALE
100
70
40
0
10
18
80
110
120
C. Doppler Effect
Doppler Effect
change 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
same frequency in
all directions
Moving source
lower
frequency
higher
frequency
Supersonic source
waves combine to
produce a shock wave
called a sonic boom
D. Seeing with Sound
Ultrasonic waves - above 20,000 Hz
Medical Imaging
SONAR
“Sound Navigation Ranging”
IV. Electromagnetic Radiation
(p.528-535)
 EM Radiation
 EM Spectrum
 Types of EM Radiation
A. Electromagnetic Radiation
Electromagnetic Radiation
transverse waves produced by the motion
of electrically charged particles
does not require a medium
speed in a vacuum = 300,000 km/s
electric and magnetic components
are perpendicular
B. Electromagnetic Spectrum
The full range of light
B. Electromagnetic (EM) Spectrum
long 
short 
low f
high f
low
energy
high
energy
C. Types of EM Radiation
Rabbits Meet In Very Unusual Xciting Gardens
C. Types of EM Radiation
Radio waves
Lowest energy EM radiation
FM - frequency modulation
AM - amplitude modulation
Microwaves
penetrate food and vibrate
water & fat molecules to
produce thermal energy
C. Types of EM Radiation
Infrared Radiation (IR)
slightly lower energy than
visible light
can raise the thermal energy
of objects
thermogram - image made by
detecting IR radiation
C. Types of EM Radiation
Visible Light
small part of
the spectrum
we can see
ROY G. BIV colors in order
of increasing
energy
red
R O Y
G.
orange
green
yellow
B
blue
I
indigo
V
violet
C. Types of EM Radiation
Ultraviolet Radiation (UV)
slightly higher energy than visible light
Types:
• UVA - tanning, wrinkles
• UVB - sunburn, cancer
• UVC - most harmful,
sterilization
C. Types of EM Radiation
Ultraviolet Radiation (UV)
Ozone layer depletion = UV exposure!
C. Types of EM Radiation
X rays
higher energy than UV
can penetrate soft tissue,
but not bones
C. Types of EM Radiation
Gamma rays
highest energy on
the EM spectrum
emitted by
radioactive atoms
used to kill
cancerous cells
Radiation treatment using
radioactive cobalt-60.
Ch. 19 - Light
II. Light and Color
(p.528-535)
 Light and Matter
 Seeing Colors
 Mixing Colors
A. Light and Matter
Opaque
absorbs or reflects all light
Transparent
allows light to pass through completely
Translucent
allows some light to pass through
B. Seeing Colors
White light
contains all visible colors - ROY G. BIV
In white light, an object…
reflects the color you see
absorbs all other colors
REFLECTS
ALL COLORS
ABSORBS
ALL COLORS
B. Seeing Colors
Stimulates red & green cones
The retina contains…
Rods - dim light, black & white
Cones - color
• red - absorb red & yellow
• green - absorb yellow & green
• blue - absorb blue & violet
Stimulates all cones
B. Seeing Colors
Color Blindness
one 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
EX: computer RGBs
View Java Applet on primary light colors.
C. Mixing Colors
Filter
transparent material
that absorbs all light
colors except the
filter color
View Java Applet on filters.
C. Mixing Colors
Pigment
colored material that absorbs
and reflects different colors
Primary pigment colors
cyan, magenta, yellow
subtractive colors
combine to form black
EX: 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)
 Reflection
 Refraction
 Diffraction
 Interference
A. Wave Interactions
Wave Interaction
When a wave meets an object or another
wave.
When a wave passes into another medium
Examples: reflection, diffraction, refraction,
interference, resonance
A. Reflection
Normal
Reflection
when a wave
strikes an object
and bounces off
incident beam
reflected beam
B. Refraction
Refraction
bending of waves when passing
from one medium to another
caused by a change in speed
• slower (more dense)  light
bends toward the normal
• faster (less dense)  light
bends away from the normal
SLOWER
FASTER
B. Refraction
Refraction depends on…
speed of light in
the medium
wavelength of
the light - shorter
wavelengths (blue)
bend more
B. Refraction
Example:
View explanation.
C. Diffraction
Diffraction
bending of waves
around a barrier
longer wavelengths
(red) bend more opposite of refraction
D. Interference
Interference
constructive  brighter light
destructive  dimmer light
E. Cool Applications!
Fiber Optics
Total 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!
Rainbows
refraction-reflection-refraction
E. Cool Applications!
Diffraction Gratings
glass or plastic made up
of many tiny parallel slits
may also be reflective
spectroscopes, reflective
rainbow stickers, CD
surfaces
E. Cool Applications!
Thin Films - Bubbles & Oil Slicks
interference results from double reflection
E. Cool Applications!
Blue Sky & Red Sunsets
• Molecules in atmosphere
scatter light rays.
• Shorter wavelengths (blue, violet)
are scattered more easily.
SUNSET
• more atmosphere
• more scattering
• orange-red sky & sun
NOON
• less atmosphere
• less scattering
• blue sky, yellow sun