Waves
Waves and Wave Properties
Why are we able to see?
Answer: Because there is light.
And…what is light?
Answer: Light is a wave.
So…what is a wave?
Answer: A wave is a disturbance
that carries energy from place to
place.
A wave does NOT carry matter with
it! It just moves the matter as it
goes through it.
What are the two
types of waves?
Types of Waves:
* Mechanical – require a medium
(ex. water and sound)
*
Electromagnetic – Do not need medium
(ex. Light, radio, x-rays)
What are the two
types of
MECHANICAL waves?
2 main types of MECHANICAL waves:
1) Transverse
2) Longitudinal
(Longitudinal is also called a Compressional wave)
Other Wave Types
Earthquakes: combination
Ocean waves: surface
Light: electromagnetic
Who can be the first group
to demonstrate a transverse
wave with your slinky?
Volunteer to
demonstrate /
create a transverse
wave?
Transverse Waves
 Oscillations are perpendicular to the
direction the wave moves
Ex:
If the wave moves left
to right
Oscillation is up &
down
http://www.physicsclassroom.com/mmedia/waves/lw.html
Using your whiteboard…
Label the parts of a
transverse wave.
Pair to legibly label all parts
earns tickets.
Highs and Lows for a
Transverse Wave
 Crests: high point
(Sometimes called wave fronts)
 Troughs: low point
Draw and label a transverse wave.
(include crest, trough, wavelength and amplitude)
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
Wavelength ( ):
 The length of one complete cycle of a wave
 Any point on the wave to the next identical point
(ex. Crest to crest, midpoint to midpoint, trough to trough)
Represented by the Greek letter “Lambda”
Wavelength does NOT effect speed!
WAVELENGTH
(shortest distance between 2 points.)
Amplitude:
Maximum displacement from rest or equilibrium
(Half the distance between highest and lowest
points)
Longitudinal Waves
Oscillations are in the same direction as
the wave moves
 Ex: Longitudinal Wave in a Slinky
 The compression will move along
the slinky forward and then back.
To create a wave, you create a
_______________
at one end of the
PULSE
ENERGY
slinky. That _______________
then is
transferred to the next coil, and the next,
and so on.
LONGITUDINAL WAVE: particle displacement is
parallel to the direction of wave propagation…
Do the particles move or oscillate about their
equilibrium (fixed point)? Pick a particle and try to
follow it….
 Instead of crests & troughs, a longitudinal
wave has compressions & rarefactions.
* compression
– a pulse of compressed air or other material
- High Pressure area
* rarefaction
- less dense area
- Low Pressure area in the air
- stretched area of a spring
Sound waves are Longitudinal
But you can hear on other
sides of the tuning fork….
Longitudinal wave from a
monopole source.
radiates sound equally well in all
directions.
What about more than one
source?
Click Here to learn more
Longitudinal Characteristics
Crest
Trough
Identify as Longitudinal or
Transverse Wave
Longitudinal
Transverse
Longitudinal
Transverse
SURFACE WAVES
 Mix both longitudinal and transverse waves
ENERGY
A wave can transmit __________
without
transferring matter?
The shortest distance between two points
on a wave where the wave pattern is
repeated is the ______________.
WAVELENGTH
What causes the disturbance?
2 ways to produce a wave:
1. Wave Pulse: single disturbance that
travels through a medium.
Ex. Rock thrown in pond
2.
Traveling Wave:
series of pulses at
regular intervals
Ex.
1. Moving rope side to side
2. Continuously ringing bells
Measures of a Wave:
Waves have frequency, wavelength, and
velocity (they are all related).
Frequency:
How often the wave goes up and down
Measured in hertz (Hz)
FREQUENCY (f)
Unit (Hertz or cycles/ sec)
NUMBER OF VIBRATIONS (WAVES)
THAT PASSES A FIXED LOCATION IN
ONE SECOND.
PERIOD (T)
Shortest time during which motion
repeats itself.
NUMBER OF SECONDS a complete
wave cycle takes to pass a fixed point
The time it
takes for the
swing to return
to the “up”
position or to
complete a
cycle.
What is the relationship between
frequency and period?
Period and frequency have an inverse relationship.
How do you define
wavelength?
Wavelength ( ):
 The length of one
complete cycle of a wave
 From crest to crest (or from any point on the wave to
the next identical point)
Represented by the Greek letter “Lambda”
Wavelength does NOT effect speed!
WAVELENGTH
(shortest distance between 2 points.)
Amplitude:
Maximum displacement from rest or equilibrium
(Half the distance between highest and lowest
points)
For example:
Cassie attaches a slinky to the wall and
begins introducing pulses with different
amplitude. Which of the two pulses (A or
B) below will reach the wall first? Justify
your answer.
How does this relate to energy?
To produce a wave with larger
amplitude, must do more work
Waves with larger amplitudes transfer
more energy
REVIEW
Do all waves require a medium?
Answer: speed = 2 m x 500 Hz = 1000 m/s
Changing Wave Direction
1. Reflection: When waves bounce off a surface.
If the surface is flat, the angle at which the
wave hits the surface will be the same as the
angle at which it leaves the surface
(angle in = angle out).
This is the law of reflection.
Start for 4th
2. Refraction: Waves can bend.
This happens when a wave
enters a new medium and its
SPEED CHANGES.
The amount of bending
depends on the medium it is
entering.
Reflection of waves
• Occurs when a wave strikes a medium
boundary and “bounces back” into
original medium.
• Completely reflected waves have the
same energy and speed as original wave.
What happens if a wave hits a
fixed boundary?
Open ended?
Reflection Types
Fixed-end reflection: The
wave reflects with inverted
phase.
Open-end reflection: The
wave reflects with the same
phase
Animation courtesy of Dr. Dan Russell,
Refraction of waves
• Transmission of wave from
one medium to another.
• Refracted waves may
change speed and
wavelength.
• Refraction is almost
always accompanied by
some reflection.
• Refracted waves do not
change frequency.
tion courtesy of Dr. Dan Russell, Kettering University
Principle of Superposition
When two or more waves pass a particular
point in a medium simultaneously, the resulting
displacement at that point in the medium is the
sum of the displacements due to each
individual wave.
The waves interfere with each other.
Types of interference.
If the waves are “in phase”, that is crests
and troughs are aligned, the amplitude is
increased. This is called constructive
interference.
If the waves are “out of phase”, that is
crests and troughs are completely
misaligned, the amplitude is decreased
and can even be zero. This is called
destructive interference.
Let’s make some predictions
with the behavior of the super
slinky!
Let’s take it into the hall!
Take your prediction sheet with you to
record observations.
Making waves!
Constructive Interference
crests aligned with crest
waves are
“in phase”
Constructive Interference
Destructive Interference
crests aligned with troughs
waves are
“out of
phase”
Destructive Interference
Let’s Review
Name 2 types of mechanical waves:
Longitudinal and transverse
Name 4 wave properties:
Wavelength
Amplitude
Frequency
Wave speed
Interference
 If two or more waves overlap, they can form
an interference pattern.
A) Constructive interference
- crests of one wave
overlap the crests of the
other
- results in increased
amplitude, or
reinforcement
B. Destructive interference
- the crest of one wave overlaps the
trough of the other wave
- results in smaller amplitude, or
cancellation
Slinky / Virtual Lab
Show the progression of the following waves interfereing
In Phase
When two oscillators are aligned
Each oscillator is always at the same
place at the same time
Out of Phase by __ degrees
90 degrees
out of phase
180 degrees
out of phase
Wave speed
 Speed:
 Describes how fast the wave can
transmit an oscillation from one place
to another
Calculating the
Speed / velocity of a Wave
Product of frequency and wavelength
OR
V=/T
Review
What 2 factors are required to determine
wave velocity?
Wave length and
frequency
SPEED
SPEED of any MECHANICAL
wave depends upon… its MEDIUM.
Summarize Calculations:
T=1 / f
f =1/T
V=/T
V=f
LET’S PRACTICE
Wave Calculation Practice #1
 If a wave generator produces 8.5 pulses
per second. What is the period of the
wave?
f = 8.5 Hz
Period = T= ?
T = 1/f
T = 1/8.5 Hz
T = 0.12 s
Never leave answer in fraction form
Wave Calculation Practice #2
A wave with a 0.78s period has a
wavelength of 3.9 m. What is the
velocity?
V=/T
T= 0.78s
V= 3.9m / 0.78s
= 3.9 m
V = 5 m/s
#3 Wave Calc WS
A wave with a frequency of 305 Hz
has a wavelength of 0.75m. What is
the wave’s velocity?
f = 305 Hz
 = 0.75m
V=?
V =  f = (0.75m)(305Hz)
V= 229 m/s
Homework
Complete Calculations Worksheet
The Electromagnetic Spectrum