Section 1: Types of Waves
Section 2: Characteristic of Waves
Section 3: Wave Interactions
Section 1: Types of Waves
KEY TERMS
Wave
Medium
Mechanical Wave
Electromagnetic Wave
Transverse Wave
Longitudinal Wave
Section 1: Types of Waves
What Is a Wave?
Is a disturbance that carries energy through matter or
space. A wave is not just the movement of matter from
one place to another.
Section 1: Types of Waves
Most waves travel through a Medium
So what is a medium?
A medium is the matter through which a wave travels.
Examples:
Sound Waves – Air
Seismic Waves – Earth
All wave that require a medium are called mechanical waves.
Section 1: Types of Waves
Light does not require a medium
Light waves consist of changing electric and magnetic
fields in space.
Light waves are called electromagnetic waves. Light
and light waves may refer to any electromagnetic wave
not just visible light.
Section 1: Types of Waves
Waves transfer energy
Energy is the ability to exert a force over a certain
distance. It is also the ability to do work.
How do we know that waves carry energy?
Section 1: Types of Waves
Energy may spread out as a wave travels
A wave front has the same amount of total energy but
is spread out over a larger area.
Section 1: Types of Waves
Vibrations and Waves
Waves are related to vibrations. Most waves are caused
by a vibrating object.
Electromagnetic – Vibrating charged particles
Mechanical – Vibrating particles in a medium
Section 1: Types of Waves
Vibrations involve transformation of energy
Figure 4 Page 457
When a mass hanging on a spring is disturbed from
rest, it starts to vibrate up and down around its
original position.
Section 1: Types of Waves
Changing from elastic potential energy to kinetic energy
and back to elastic and gravitational potential energy.
A mass bouncing up and down cause a vibration called
simple harmonic motion.
Section 1: Types of Waves
A wave can pass through a series of vibrating objects
As energy is transferred from the first object to the
second object the first object slows down.
A vibration that fades out is called damped harmonic
motion.
The motion of particles in a medium is like the
motion of masses on springs.
Section 1: Types of Waves
Transverse and Longitudinal Waves
Particles in a medium can vibrate either up and down or
back and forth.
How are waves classified?
By the direction that the particles move in the medium as
the wave passes.
Section 1: Types of Waves
Transverse waves have perpendicular motion
Waves in which the motion of the particles is
perpendicular to the motion of the wave as a whole are
called Transverse waves.
Example – Light waves
Section 1: Types of Waves
Longitudinal waves have parallel motion
Waves that cause the particles in a medium to vibrate
parallel to the direction of the wave motion are called
longitudinal waves.
Example – Sound waves
Section 1: Types of Waves
In a surface wave, particles move in circles
Surface waves occur at the boundary between two
different mediums, such as water and light.
Surface wave particles have both perpendicular and
parallel motion in relation to the wave motion.
Section 2: Characteristic of Waves
KEY TERMS
Crest
Trough
Amplitude
Wavelength (λ)
Period
Frequency
Doppler Effect
Section 2: Characteristic of Waves
Wave Properties
An ideal transverse wave has the shape of a sine
curve.
A sine curve looks like an S lying on its side. A
wave with this shape is referred to as a sine wave.
Section 2: Characteristic of Waves
Amplitude measures the amount of particle
vibration
Highest point on a transverse wave is the crest
Lowest point on a transverse wave is the trough
The greatest distance that particles are displaced from
their normal resting positions because of a wave is
called amplitude.
Section 2: Characteristic of Waves
Amplitude is also half the distance between the crest
and trough .
Large waves have larger amplitudes and carry more
energy
Longitudinal waves do not have crest and troughs
because they cause particles to move back and forth
instead of up and down.
Section 2: Characteristic of
Waves
Crowded areas of a longitudinal wave is called
compressions an the stretched-out areas are called
rarefractions
Wavelength measures the distance between two
equivalent parts of a wave
The distance from one crest to the next crest, or from
one trough to the next trough is called the wavelength.
Section 2: Characteristic of Waves
For longitudinal waves, the wavelength is between two
compressions or two rarefractions.
Not all waves have a single wavelength that is easily
measured.
If the source of a wave vibrates in an irregular way, the
wave length may change over time.
Wavelength is represented by the Greek Letter
Lambda (λ) and is measured in meters.
Section 2: Characteristic of Waves
The period measures how long it takes for waves to
pass by
The period is a also the time required for one complete
vibration of a particle in a medium
In an equation the period is represented by a (T)
because period is a measure of time (seconds).
Section 2: Characteristic of Waves
Frequency measures the rate of vibrations
The frequency of a wave is the number of full
wavelengths that pass a point in a given time interval.
It also measures how rapidly vibrations occur in the
medium, at the source of the wave or, both.
Frequency (f) is measured in Hertz (Hz) and named
for Heinrich Hertz
Section 2: Characteristic of Waves
Heinrich Hertz became the first person to
experimentally demonstrate the existence of
electromagnetic waves in 1888.
The frequency and period of a wave are related.
The more vibrations in a second the shorter the
amount of time .
Section 2: Characteristic of Waves
Frequency is the inverse of the period.
Frequency-Period Equation
Section 2: Characteristic of Waves
Light comes in a wide range of frequencies and
wavelengths
We detect light with a frequency from about
4.3 χ 10¹⁴ Hz to 7.5 χ 10¹⁴ Hz. This is visible light
What accounts for the different colors we see?
Difference in frequencies
The full range of light at different frequencies and
wavelengths is called the electromagnetic spectrum
Section 2: Characteristic of Waves
Wave Speed
Wave speed equals frequency times wavelength
Section 2: Characteristic of Waves
Wave speed is simply how fast is a wave moving
For a wave we use wavelength (λ) as our distance and
the period as our time.
Section 2: Characteristic of Waves
Because the period is the inverse of the frequency,
dividing by the period is equivalent to multiplying by
the frequency
Wave Speed Equation
wave speed = frequency χ wavelength
v=f χ λ
Section 2: Characteristic of Waves
Solving for frequency
Section 2: Characteristic of Waves
The speed of a wave depends on the medium
Sound travels in air at a rate of 340m/s
In water it is 3 to 4 times faster and in a solid it is 15 to
20 times faster.
In a given medium, the speed of the wave is constant,
it does not depend on the frequency of the wave.
Section 2: Characteristic of Waves
Kinetic theory explains differences in wave speed
What determines how well a wave will travel in a
medium?
The arrangement of particles
Gases – waves do not travel well because of the empty
space
Section 2: Characteristic of Waves
Liquids – vibrations are transferred quickly from one
molecule to the next. Waves are able to travel
faster in liquid than in gases.
Solids – Molecules are close together and in a fixed
position. As a result, waves travel very quickly
through most solids.
Section 2: Characteristic of Waves
Light has a finite speed
All electromagnetic waves in empty space travel at the
same speed, the speed of light 3.00 x 10⁸m/s
(186,000mi/s)
Light travels slower when it passes through a medium
Section 2: Characteristic of Waves
The Doppler Effect
Pitch is determined by the frequency of sound
waves.
Pitch of a sound, how high or low it is, is
determined by the frequency at which the
sound waves strike the eardrum.
Section 2: Characteristic of Waves
Frequency changes when the source of the wave is
moving.
A change in the observed frequency of a wave results
from the motion of the source or observer is called the
Doppler Effect.
Section 3: Wave Interactions
Key Terms
Reflection
Diffraction
Refraction
Interference
Constructive Interference
Destructive Interference
Standing Wave
Section 3: Wave Interactions
Reflection, Diffraction, and Refraction
Reflection is simply the bouncing back of a wave when
it meets a surface or boundary.
Waves reflected at a free boundary
The reflected wave is exactly like the original wave
except it travels in the opposite direction
Section 3: Wave Interactions
At a fixed boundary, waves reflect and turn upside
down
Diffraction is the bending of waves around an edge
When waves pass the edge of an object or pass through
an opening, they spread out as if a new wave was
created.
Section 3: Wave Interactions
Waves can also bend by refraction
Refraction is the bending of a wave front as the wave
front passes between two substances in which the
speed of the wave differs.
All waves are refracted when they pass from one
medium to another at an angle.
Section 3: Wave Interactions
Interference
More than one wave can exist in the same place at the
same time.
Waves in the same place combine to produce a
single wave.
Interference is the combination of two or more waves
of the same frequency that result in a single wave.
Section 3: Wave Interactions
Crest are positive and troughs are negative
This method of adding waves is sometimes known as
the principle of superposition.
Constructive interference increases amplitude
When the crest of one wave overlaps the crest of
another wave, the waves reinforce each other
Section 3: Wave Interactions
Constructive interference is any interference in which
waves combine so that the resulting wave is bigger
than the original wave.
Destructive interference decreases amplitude
When the crest of one wave meets the trough of
another wave, the resulting wave has a smaller
amplitude then the larger of the two waves.
Section 3: Wave Interactions
Destructive interference is any interference in which
waves combine so that the resulting wave is smaller
than the largest of the original waves.
When destructive interference occurs between two
waves that have the same amplitude, the waves may
completely cancel each other out.
Interference of light waves creates colorful displays
Section 3: Wave Interactions
Interference of sound waves produce beats
When the compressions from two tuning forks arrive
at the same time, constructive interference occurs, and
the sound is louder.
When a compression and rarefraction arrive at the
same time, destructive interference occurs, and the
sound is softer.
The series of loud and soft sounds are called beats
Section 3: Wave Interactions
Standing Waves
Interference can cause standing waves.
Standing waves can form when a wave is reflected at
the boundary of a medium
The original wave is interfering with the reflected wave
causing the medium to vibrate in a stationary pattern
that resembles a loop or series of loops
Section 3: Wave Interactions
Waves are traveling in both directions
Standing waves have nodes and antinodes
The point of separation between each loop is the node
At the node complete destructive interference occurs.
No vibration occurs .
Section 3: Wave Interactions
The point midway between the nodes is called an
antinode. Antinodes lay at the top or bottom of each
loop.
At the antinode complete constructive interference
occurs producing maximum vibration.
Standing waves can have only certain wavelengths
Section 3: Wave Interactions
The simplest standing wave occurs when the
wavelength is twice the length of the string.
At a certain frequency, the wavelength is exactly equal
to the length of the string producing a node in the
middle of the string.
Standing waves can exist whenever a multiple of halfwavelengths will fit exactly in the length of the string.