### PS Unit 4 Waves, Sound and Light

```Waves, Sound and Light
Chapters 15 and 16
Standards:
SPS9. Students will investigate the properties of waves.
SPS9a. Recognize that all waves transfer energy.
SPS9b. Relate frequency and wavelength to the energy of
different types of electromagnetic waves and mechanical
waves
SPS9c. Compare and contrast the characteristics of
electromagnetic and mechanical (sound) waves.
SPS9d. Investigate the phenomena of reflection, refraction,
interference, and diffraction.
SPS9e. Relate the speed of sound to different mediums.
SPS9f. Explain the Doppler Effect in terms of everyday
interactions.
Waves
Waves
• rhythmic disturbances that carry energy through
matter or space
Medium
• material through which a wave transfers energy
• solid, liquid, gas, or combination
• mechanical waves need a medium
• electromagnetic waves don’t need a medium (e.g.
Wave Characteristics
•
•
•
•
•
•
transfer energy
the bigger the wave, the more energy carried
create an erosion force
most are caused by vibrating objects
tsunami: ocean wave caused by earthquakes
wave front: circles spreading out from a wave
(each wave front carries same amount of
energy)
Waves
• Two Types:
Longitudinal
Transverse
Anatomy of Waves
• crest: high points on transverse wave
• trough: low points on transverse wave
• compressions: crowded areas on longitudinal
wave
• rarefactions: stretched-out areas on
longitudinal wave
Transverse Waves
Transverse Waves
• medium moves
perpendicular to the
direction of wave
motion
ex. electromagnetic
waves
Transverse Waves
• Wave Anatomy
corresponds to
the amount of
energy carried
by the wave
wavelength
crests
amplitude
amplitude
nodes
troughs
wavelength
Longitudinal Waves
Longitudinal Waves (a.k.a. compressional)
• medium moves in the same direction as wave
motion
ex. sound waves
Longitudinal Waves
• Wave Anatomy
compression
rarefaction
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) unit
 shorter wavelength 
higher frequency 
higher energy
1 second
Measuring Waves
Period
• time it takes for 1 complete wave cycle
Measuring Waves
Amplitude:
• greatest distance particles in wave move from
rest
• larger amplitude  greater energy
Measuring Waves- Speed
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)
Practice: Measuring Waves
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
Practice: Measuring Waves
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
Measuring Waves: Speed-Period
• v= λ
T
λ – wavelength
T -- period
λ
V
T
Measuring Waves: Frequency-Period
Frequency-Period
• period: time it takes for a wave to pass a
certain (T) related to...
• frequency: number of wavelengths that pass a
given (f)
• f= 1
1
period
f
T
Wave Speed Facts
• depends on medium:
Fastest- solid > liquid > gas –slowest
• speed of light (c) = 3.00 x 108 m/s (finite speed)
• visible light is detected by eye
• Full light range = electromagnetic spectrum
• speed of sound in air = 340m/s
Visible Light
The Doppler Effect
• Doppler Effect: change in frequency of a
sound wave when the source or observer is
moving
• pitch (how high or low): determined by
frequency at which sound strikes eardrum
FYI
shifts to track storms since radio waves reflect
off of rain, snow and hail
Wave Interactions
• Reflection: bouncing back of wave when it
meets a boundary
• Refraction: bending of waves when they pass
from one medium to another
• Diffraction: bending of waves when they pass
around an edge
Reflection
Refraction
Diffraction
Interference
Combination of two or more waves that
combine into a single wave:
• Constructive- increases amplitude
• Destructive- decreases amplitude (cancels each
other out)
Light Interference
• constructive and destructive waves create
different frequencies (colors)
ex. rainbow seen in oil on water, iridescent
colors on peacock feather
Sound Interference
• When wave compressions from 2 sources
arrive at ear at same time = louder sound
(constructive interference)
• When wave compression and rarefaction from
2 sources arrive at ear at same time = beat
(destructive interference)
Standing Waves
• Results from interference between wave and
its reflection
• Causes medium to vibrate in a stationary
pattern (loop or series of loops)
• Nodes: crest of wave meets its reflected
trough (complete destructive interference)
• Antinodes: crest of wave lines up with
reflected crest; points of maximum vibration;
(complete constructive interference)
Standing Waves
Properties of Sound
•
•
•
•
longitudinal waves
require medium
spread in air in all directions from source
travel slower in gas; faster in most solids
(foam, rubber damper vibrations)
• travel faster at hot temperatures (greater
collision of molecules)
Speed of Sound
Pitch
•
•
•
•
•
Pitch: wave frequency
↑ f = ↑ pitch
Range of pitch for humans: 20hz – 20,000hz
Infrasound: sound below human hearing
Ultrasound: sound above human hearing
Ranges of Hearing for Mammals
Loudness
• Loudness: determined by intensity (amplitude
and distance from sound source)
* measured in decibels, dB
* threshold of human hearing- 0 dB
* threshold of pain- 120 dB
Musical Instruments
• Produce sound through vibrations of string, air
columns, membranes
• Rely on standing waves
• Use resonance to amplify sound
• Resonance: when two objects naturally
vibrate at same frequency (depends on size,
shape, mass and materials)
(electric guitars don’t resonate well so they
require separate amplifiers)
Hearing and the Ear
Senses vibrations, amplifies them, transmits
them to the brain:
• Outer ear: Pinna collects sound waves, sends
to ear canal, causes tympanum to vibrate
• Middle ear: vibrations pass to hammer, anvil,
stirrup (small bones act as levers to increase
vibrations)
• Inner ear: vibrations in cochlea are converted
into electrical signals to brain
The Ear
Ultrasound
• High f of ultrasound
can travel through
most material
• Used to measure
distance
• Reflected waves
create image
• Sonagram: used in
medicine to view
internal organs
Ultrasound-Sonar
and ranging
• Uses reflected sound
waves for
measurement of
distances
• Used by marine
mammals
Sound Project
With a partner: Create a musical instrument
from scratch that can produce a recognizable
tune (ex. Mary Had a Little Lamb, Row, Row,
• Suggested Materials: 5-8 bottles
water
• Time: 2 class periods
The Nature of Light
Has dual nature:
1. Thomas Young’s experiment showed light moves in
electromagnetic waves
*explains how light waves interfere with each other
2. Light can also be modeled as a stream of particles
* photons: bundles of high energy light units
Properties of Light
• transverse waves produced by motion of
electrically charged particles
• does not require a medium
Speed of Light
• depends on medium
• ≈ 3.0 x 10⁸ m/s in a
vacuum (nothing
known is faster)
• travels slower
outside a vacuum
(1.24 x 10⁸ m/s
through a diamond)
Brightness
Intensity: measure of
brightness
• decreases with distance
from light source due to
decrease in photons
passing through an area
• made up of electric and magnetic particles
• consists of waves of all possible energies,
frequencies and wavelenghts
• each part of spectrum has unique qualities
• used in technologies
• longest wavelengths
• Include TV and radio signals- AM (amplitude
modification), FM (frequency modification)
Microwaves:
• carry telecommunication signals long
distances
• penetrate food, vibrate water & fat molecules
to produce thermal energy
• slightly lower energy than
visible light
• can raise the thermal energy
of objects
• felt as warmth
• thermogram - image made by
• slightly higher energy than visible light
• Types:
UVA - tanning, wrinkles
UVB - sunburn, cancer
UVC - most harmful,sterilization
• absorbed in ozone layer
X rays
• higher energy than UV
• can penetrate soft tissue,
but not bones
Gamma rays
• highest energy
• emitted by
• used to kill cancerous
cells (kills healthy
cells too)
• Visible Light
– small part of the
spectrum we
can see
– ROY G. BIV colors in order
of increasing
energy
R
red
O
Y
orange yellow
G.
green
B
blue
I
indigo
V
violet
```