Sec. 14.1
Wave Properties
Waves
Objectives
PART I
Wave Properties
Wave Anatomy
PART II
Wave Math
Wave Behavior
PART III
Sound Waves
Light Waves
(aka Electromagnetic Waves or Radiation)
Identify how waves transfer energy without
transferring matter.
Contrast transverse and longitudinal waves.
Relate wave speed, wave-length, and
frequency.
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PART I
Wave Properties
Wave Anatomy
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Waves are everywhere in nature
Sound waves,
visible light
waves,
radio waves,
microwaves,
water waves,
sine waves,
GOALS:
What is a wave?
What are the different types of waves?
What are the parts of a wave?
telephone chord
waves,
stadium waves,
earthquake
waves,
waves on a
string,
slinky waves
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What is a wave?
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Example: Slinky Wave
Slinky is the medium (steel)
the wave is the disturbance traveling
through it
the wave carries energy through the
medium
a wave is a disturbance
pattern that travels through a
medium.
Waves carry energy
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Medium
2 Types of Wave:
= the substance that the wave travels through
Wave
Medium
Water Wave……………………… Water
Sound Wave ……………………… Air
Slinky Wave ……………………… Steel
Stadium Wave …………………… People
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Transverse Wave:
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Transverse Wave:
Medium moves
perpendicular
to direction of
wave energy
*denser medium will slow wave down
Longitudinal
(Compression) Wave
Longitudinal (Compression) Wave
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Medium moves
parallel to
direction of
wave energy
*denser medium will speed wave up
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Longitudinal (Compression) Waves
Math
This slinky wave is a longitudinal
(compression) wave in which steel is the
medium.
A sound wave is a longitudinal (compression)
wave in which air is the medium.
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What moves where?
Transverse Waves:
Wave moves
forward
Medium moves up
and down
Surface Waves
Combination of both… longitudinal
and transverse.
Longitudinal at depth;
Transverse at surface.
Longitudinal (Compression) Waves:
Wave moves forward
Medium moves side to side
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Wave Anatomy:
Anatomy of a Wave
We will use a transverse wave to describe
this since it is easier to see the pieces.
Compression Wave as a Transverse Wave Link:
http://www.ngsir.netfirms.com/englishhtm/Lwave.htm
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What about longitudinal waves?
http://www.ngsir.netfirms.com/englishhtm/Lwave.htm
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Anatomy of a Wave
Anatomy of a Continuous Wave
crest
The points A and F are called the CRESTS
of the wave.
This is the point where the wave exhibits the
maximum amount of positive or upwards
displacement
In our wave here the dashed line represents the
equilibrium position. (origin)
Once the medium is disturbed, it moves away
from this position and then returns to it
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Anatomy of a Wave
Anatomy of a Wave
Amplitude
trough
The points D and I are called the
TROUGHS of the wave.
These are the points where the wave
exhibits its maximum negative or downward
displacement.
The distance between the dashed line and
point A is called the Amplitude of the wave.
This is the maximum displacement that the
wave moves away from its origin.
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Anatomy of a Wave
Drawing Waves
wavelength
The distance between two
λ consecutive similar
points (in this case two crests) is called the
wavelength.
This is the length of theλwave pulse.
Between what other points is can a wavelength be
measured?
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Wave
Anatomy:
Summary
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Anatomy of a Wave
(Later we’ll add nodes and antinodes)
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What else can we determine?
Remember; Waves move, and the medium
moves to, over time
The words period and frequency take the
passage of time into account.
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Period and Frequency
PART II:
http://www.ngsir.netfirms.com/englishhtm/T
waveA.htm
Wave Math
Wave Behavior
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PART II
Wave Math
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Period ( T ):
= The amount of time it takes for one wave
to pass a point
Units: seconds (s)
GOALS:
Frequency (  ):
How can we describe wave motion?
How can we predict wave motion?
= Waves per second
(How many waves pass by a point per second)
Units: Hertz (Hz)
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Period and Frequency
are related
1 Hertz = 1wave per second
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Wave frequency
Frequency measures how often something
happens over a certain amount of time.
 = 1/T
 = (# of waves passed) / (time passed)
T= 1/
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We can measure how many times a
wavelength passes a point per second, and
this will give us the frequency.
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Wave frequency
Wave Period
Suppose I wiggle a slinky back and forth, and
count that 6 waves pass a point in 2 seconds.
What would the frequency be?
6 waves / 2 second
3 waves / 1 second
 = 3 Hz
Remember: Hertz (Hz) means waves per second.
The period is the time it takes for one
wave to pass by.
If there are 3 waves per second, then one
wave only takes a third of a second.
T = 0.333
f=3
T=1/f
f=1/T
=1/3
= 1 / 0.333
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Period and Frequency
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Wavelength (  )
A continuous wave is traveling so
fast that a crest passes by one point
every 0.5 seconds.
The distance from the crest of
one wave to the crest of the
next or from the trough of a
wave to the next trough
What is the frequency of the wave?
What is the period of the wave?
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wave speed or velocity (  )
Different waves travel at different
speeds. There is a relationship
between speed, wavelength and
frequency.
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The Wave Equation:
v f
= Wave speed or velocity
= Wavelength (m)
= Frequency (Hz)
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(m/s)

 
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v f
v f
What is the frequency of a wave if it has a
speed of 12 cm/s and a wavelength of 3 cm?
(12 cm/s) / (3cm) = 4 Hz
A wave has a frequency of 5 Hz and a wave
speed of 18 m/s. What is it’s wavelength?
(18 m/s) / (5 Hz) = 3.6 m
The frequency is 4 waves per second
The wavelength is 3.6 meters.
Remember: Hertz means “waves per second”37
Wave Behavior: Boundaries
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Wave Behavior: Boundaries
The behavior of a wave when it reaches
the end of its medium is called the wave’s
BOUNDARY BEHAVIOR.
When one medium ends and another
begins, that is called a boundary.
 Boundaries change speed and wavelength
 Frequency stays the same
 Type of barrier determines type of change
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Fixed
End
Wave Behavior: Boundaries
The wave before it hits the boundary is called the
INCIDENT WAVE.
Sometimes the energy may be reflected backwards
as a REFLECTED WAVE.
The wave energy that continues into the new
medium is called the TRANSMITTED WAVE.
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One type of boundary that a wave may
encounter is that it may be attached to a
fixed end.
In this case, the end of the medium will
not be able to move.
What is going to happen if a wave pulse
goes down this string and encounters the
fixed end?
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Fixed End Reflection
Fixed End
Here the incident pulse is an upward
pulse.
The reflected pulse is upside-down. It is
inverted.
The reflected pulse has the same speed,
wavelength, and amplitude as the
incident pulse.
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When a wave enters a more dense or rigid
medium, the boundary acts as a fixed end
boundary, and produces fixed end reflection: the
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reflected wave is inverted.
Free End
Free End
Another boundary type is when a wave’s
medium is attached to a stationary object
as a free end.
In this situation, the end of the medium is
allowed to slide up and down.
What would happen in this case?
Here the reflected pulse is not inverted.
It is identical to the incident pulse, except
it is moving in the opposite direction.
The speed, wavelength, and amplitude are
the same as the incident pulse.
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Free End Animation
When a wave enters a less dense or less rigid
medium, the boundary acts as a free end
boundary, and produces free end reflection: the
reflected wave is not inverted.
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Change in Medium
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Change in Medium
Change in
Medium
A change in medium is a type of boundary.
Consider a thin rope attached to a thick
rope. The point where the two ropes are
attached is the boundary.
At this point, a wave pulse will transfer
from one medium to another.
What will happen here?
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Change in
Medium
In this situation part of the wave is reflected,
and part of the wave is transmitted.
Part of the wave energy is transferred to the
more dense medium, and part is reflected.
The transmitted pulse is upright, while the
reflected pulse is inverted.
Change in Medium Animation
The speed and wavelength of the reflected
wave remain the same, but the amplitude
decreases.
The speed, wavelength, and amplitude of
the transmitted pulse are all smaller than
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in the incident pulse.
Wave Behavior:
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Constructive Interference
Let’s consider two waves moving towards
each other, both having a positive
upward amplitude.
What will happen when they meet?
Interference and Superposition
or
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Constructive Interference
Destructive Interference
They will ADD together to produce a
greater amplitude.
This is known as CONSTRUCTIVE
INTERFERENCE.
Now let’s consider the opposite, two
waves moving towards each other, one
having a positive (upward) and one a
negative (downward) amplitude.
What will happen when they meet?
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Destructive Interference
Occurs when the crests of one wave and the
Interference
troughs of another wave overlap
Destructive Interference
This time when they meet they will
produce a smaller amplitude.
This is know as DESTRUCTIVE
INTERFERENCE.
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SIM
Interference
Here’s what it
looks like:.
SIM - Interference
(SIM1)
(SIM2)
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Constructive interference:
Interference is Everywhere
•Waves are In Phase
•Crest lines up with crest
•Amplitudes Add
Complex interference patterns in
sound waves make up complex
sounds and noises.
Destructive interference:
•Waves are Out of Phase
•Crest and Trough line up
•Amplitudes “Cancel Out”
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Interference
Constructive - waves add in phase, producing larger peaks than any
wave alone.
Destructive - waves add out of phase, producing smaller peaks than a
single wave alone.
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Check Your Understanding
 Which points will produce constructive interference and
which will produce destructive interference?
 Constructive
G, J, M, N
 Destructive
H, I, K, L, O
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Beating Frequency (SIM1) (SIM2)65
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