Download Unit 5 - Mr. Abbott's Mathematics and Physics Page

Unit 6
Waves and Light
Waves
 Wave –
a repeating disturbance or movement that
transfers energy through matter or space
Waves
o All waves transfer energy without
transporting matter from place to place
Waves
• Example:
Throwing a pebble into a puddle of water
Waves
• The pebble transfers some of its energy
to nearby water molecules, causing
them to move
• These molecules then pass the energy
along to neighboring water molecules,
which, in turn, transfer it to their
neighbors
Waves
• The energy moves farther and farther
from the source of the disturbance
• What you see is energy traveling in the
form of a wave on the surface of the
water
Waves
 The waves DO NOT carry the water
along with them – they ONLY transfer
energy
Waves
• A wave will travel only as long as it has
energy to transfer
• This is why the ripples on a puddle eventually
die out after traveling for a short distance
Waves
• All waves are produced by something that
vibrates
Waves
Waves
Q:
What are mechanical waves?
A:
Waves that require a medium in
which to travel.
Waves
• A medium is the matter that waves
travel through
• Mediums can be solid, liquid, or gas
Waves
• Examples of mechanical waves include
sound waves, seismic waves, ocean
waves, etc…
Waves
Q: Describe two types of mechanical
waves.
A:
Transverse waves and
compressional (or longitudinal)
waves
Waves
 Transverse Waves –
matter in the medium moves back and
forth at right angles to the direction that
the waves travels in
Waves
• Example: ocean waves
Waves
• A wave in the ocean moves horizontally, but the
water that the wave passes through moves up and
down
• Think of people doing “the wave” at a football
game
Waves
• Compressional Waves –
matter in the medium moves back and
forth along the same direction the wave
travels
• Also known as “longitudinal waves”
Waves
Waves
Example: Sound Waves
• When you talk, the air molecules are pushed
together by the vibrations
• The compressions travel through the air to make a
wave
Waves
Q:
Are there waves that don’t
require a medium in which to
travel?
A:
Yes.
Waves
• Electromagnetic waves can travel
through a vacuum or empty space, as
well as through matter
Waves
• Carry energy from place to place like
mechanical waves
• Differ from mechanical waves in how they
are produced and how they travel
• Considered transverse waves
Waves
Parts of a Wave
Q:
What are the parts of a wave?
A:
Crests and troughs or
compressions and rarefactions.
Parts of a Wave
• Transverse waves have crests and
troughs
Parts of a Wave
• Crests –
high points in the wave
• Troughs –
low points in the wave
Parts of a Wave
Parts of a Wave
Parts of a Wave
• Compressional waves have compressions
and rarefactions
Parts of a Wave
• Compression –
region where the medium becomes crowded
together, or more dense
• Rarefaction –
the less-dense regions of a compressional
wave
Parts of a Wave
Parts of a Wave
Measuring Waves
Q:
How can we measure waves?
A:
We use wavelength, frequency,
amplitude, and speed
Measuring Waves
• Wavelength –
the distance between one point on a
wave and the nearest point just like it
Measuring Waves
Measuring Waves
• With transverse waves, we measure
wavelength from crest to crest or trough to
trough
Measuring Waves
• With compressional waves, we measure
wavelength from the start of one
compression to the start of the next
compression, or from the start of one
rarefaction to the start of the next rarefaction
Measuring Waves
• Frequency –
the number of wavelengths that pass a
fixed point each second
Measuring Waves
• Simply count the number of crests or troughs
(or compressions or rarefactions) that pass by
a given point each second
Measuring Waves
• The unit for frequency is Hertz (Hz)
• One Hz means that one wavelength passes by in
one second
• Hz = 1/s
Measuring Waves
• As frequency of a wave increases,
wavelength decreases
Measuring Waves
Measuring Waves
• Frequency is always equal to the rate of
vibration of the source that creates it
Measuring Waves
Measuring Waves
• Speed –
how fast a wave travels
Measuring Waves
• Speed of a wave depends on the medium
it is traveling through
• Example:
Sound waves generally travel faster in a
material when the temperature of the
material is greater
Measuring Waves
• Calculating Wave Speed:
Speed (m/s) = Frequency (Hz) x Wavelength (m)
or
v=fx
Measuring Waves
Sample Problem
What is the speed of a sound wave that
has a wavelength of 2 m and a frequency
of 170.5 Hz?
Measuring Waves
What information are you given?
Wavelength = 2m
Frequency = 170.5 Hz
1.
Measuring Waves
2) What is the unknown you are trying
to solve for?
Speed (velocity)
Measuring Waves
3)
Write an equation that contains both
the given quantities and the
unknown variable.
v=fx
Measuring Waves
Substitute in the known quantities
and solve the equation.
V= 170.5Hz x 2m
4)
V =341 m/s
Measuring Waves
Practice Problem #1:
Waves in a lake have a wavelength of 6 m
apart and pass a person on a raft with a
frequency of 0.5 Hz. What is the speed of
the waves?
What information are you
given?
Wavelength = 6m
Frequency = .5 Hz
What is the unknown you
are trying to solve for?
Speed (velocity) of wave
Write an equation that
contains both the given
quantities and the unknown
variable.
v=fx
Substitute in the known
quantities and solve the equation.
V= .5 Hz x 6m
V= 3 m/s
Measuring Waves
Practice Problem #2:
A buoy bobs up and down in the ocean.
The waves have a wavelength of 2.5 m,
and they pass the buoy at a speed of 4.0
m/s. What is the frequency of the waves?
How much time does it take for one wave
to pass under the buoy?
Wavelength = 2.5 m
Velocity = 4.0 m/s
v=fx
4.0 m/s = f x 2.5m
f= 4.0m/s
2.5m
1wave/1.6hz
f= 1.6 Hz
1 wave passes
every .63 seconds
Measuring Waves
Practice Problem #3:
The musical note A above middle C has a
frequency of 440 Hz. If the speed of
sound is known to be 350 m/s, what is
the wavelength of this note?
Frequency = 440 Hz
Velocity = 350 m/s
v=fx
350 m/s = 440 Hz x 
= 350 m/s
440Hz
= .8 m
Measuring Waves
• Amplitude –
related to the energy transferred by a
wave
Measuring Waves
• The greater the wave’s amplitude, the more
energy the wave transfers
• Amplitude is measured differently for
transverse and compressional waves
Measuring Waves
• Transverse Waves - distance from the
crest or trough of the wave to the rest
position of the medium
• Think about the difference between a tall and
a short wave when standing in the water?
Which has more energy to knock you over?
Measuring Waves
Measuring Waves
• Compressional Waves - related to how
tightly the medium is pushed together at
the compressions
• The denser the medium at the compressions, the
higher the amplitude of the wave and the more energy
that is transferred
Measuring Waves
Waves
Q:
What’s in a wave?
A:
Energy, energy, energy…
ELECTROMAGNETIC WAVES
Q:
Remind me again of the basic
properties of waves…
A:
Here’s a short summary on how
waves work:
ELECTROMAGNETIC WAVES
• All waves are produced by something that
vibrates
• Waves transmit energy from one place to
another
ELECTROMAGNETIC WAVES
• Some types of waves require a medium
in which to travel, while other types of
waves do not
• Sound waves require air particles to travel
through
ELECTROMAGNETIC WAVES
• Water waves must have water molecules
• These waves travel because energy is transferred
from particle to particle
• Without matter, these waves could not move
ELECTROMAGNETIC WAVES
 Electromagnetic waves do NOT
require a medium to transfer energy –
they can travel through space where no
matter is present
ELECTROMAGNETIC WAVES
Q:
How do electromagnetic waves
transfer energy without matter?
A:
They use electric and magnetic
fields.
ELECTROMAGNETIC WAVES
 Instead of transferring energy from
particle to particle, electromagnetic waves
travel by transferring energy between
vibrating electric and magnetic fields
ELECTROMAGNETIC WAVES
o Magnetic fields exist around all magnets,
even if the space around the magnet contains
no matter
ELECTROMAGNETIC WAVES
• Think about a paper clip being attracted
to a magnet without the two even
touching – this occurs because of the
magnetic field around the magnet
ELECTROMAGNETIC WAVES
• Electric charges are surrounded by
electric fields
ELECTROMAGNETIC WAVES
 This allows the charges to exert forces on
each other even when they are far apart
ELECTROMAGNETIC WAVES
o Electric charges are also surrounded by
magnetic fields
ELECTROMAGNETIC WAVES
• It’s the motion of electrons that generates
the magnetic field
• An electric current flowing through a wire
is surrounded by both an electric field, as
well as a magnetic field
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC WAVES
• A changing magnetic field creates a changing
electric field and vice versa
• When an electric charge vibrates back
and forth, the electric field around it
changes
ELECTROMAGNETIC WAVES
• Because the electric charge is in motion, it
also has a magnetic field around it
• This magnetic field also changes as the
electric charge vibrates
ELECTROMAGNETIC WAVES
• But how does this become an
electromagnetic wave?
• The changing electric field around the
charge creates a changing magnetic
field, which in turn creates a changing
electric field
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC WAVES
• This process continues, with each
creating the other
• These vibrating electric and magnetic
fields travel outward from the moving
charge and vibrate at right angles to
the direction the wave travels
ELECTROMAGNETIC WAVES
 This makes an electromagnetic wave
(which is also a transverse wave)
ELECTROMAGNETIC WAVES
Q:
What are some properties of
electromagnetic waves?
A:
Electromagnetic waves have
speed, wavelength, and frequency
like mechanical waves.
ELECTROMAGNETIC WAVES
• Wave Speed
• All electromagnetic waves travel at 300,000
km/s in the vacuum of space
• This is also known as the speed of light
ELECTROMAGNETIC WAVES
• Nothing travels faster than the speed of
light in nature
ELECTROMAGNETIC WAVES
• When an electromagnetic wave travels
through matter, this speed changes
• The speed will depend on the material the
wave is passing through
ELECTROMAGNETIC WAVES
• Electromagnetic waves usually travel
most slowly through solids and fastest
through gases
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC WAVES
• Wavelength and Frequency
• Like all waves, electromagnetic waves can be
described by their wavelengths and
frequencies
ELECTROMAGNETIC WAVES
 Wavelength –
Distance from one crest to another
ELECTROMAGNETIC WAVES
• Frequency – number of wavelengths that
pass a given point in one second
• Also can be described as the number of
vibrations made by the electric charge
in one second
ELECTROMAGNETIC WAVES
• The wavelength and frequency of an
electromagnetic wave are related
• As the frequency increases, the
wavelength decreases and vice versa
ELECTROMAGNETIC WAVES
• Electromagnetic waves can behave as
waves and as particles
• These particles are referred to as photons
ELECTROMAGNETIC WAVES
• The amount of energy in a photon is
dependent on the frequency of the
wave (rather than the amplitude)
ELECTROMAGNETIC WAVES
• The higher the frequency, the greater the
energy in the photon
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC
SPECTRUM
Q:
Now that I understand
electromagnetic waves, what
exactly is the electromagnetic
spectrum?
A:
The entire range of
electromagnetic wave
frequencies.
ELECTROMAGNETIC
SPECTRUM
• The electromagnetic spectrum is
composed of 7 types of electromagnetic
waves that interact with matter very
differently
ELECTROMAGNETIC
SPECTRUM
• They are separated from one another
based on their wavelengths and
frequencies
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• Radio Waves
• Low-frequency electromagnetic waves with
wavelengths longer than 1 mm
ELECTROMAGNETIC
SPECTRUM
• Radio waves with wavelengths less than 30
cm are called microwaves
ELECTROMAGNETIC
SPECTRUM
• Microwaves are best known for cooking
food in microwave ovens
• Microwaves are also used for
communication in cellular phones and
satellite signals
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• Radio waves also have other uses
• To find the movement and position of
objects using radar
ELECTROMAGNETIC
SPECTRUM
• To take a picture of the bones and soft
tissue on the inside of a patient’s body
using MRI
ELECTROMAGNETIC
SPECTRUM
• To carry audio signals from radio
stations to your radio
• But remember, you can’t hear a
radio wave
ELECTROMAGNETIC
SPECTRUM
• The audio signal that the radio wave
carries is converted into sound
through your radio
• What you can hear is the sound wave
coming from the radio as it moves
through the air
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• Infrared Waves
• Have higher frequencies than radio waves
and lower frequencies than red light
ELECTROMAGNETIC
SPECTRUM
• Wavelengths vary from 1 mm to 750 nm
• 1 nanometer = 10-9 meters
ELECTROMAGNETIC
SPECTRUM
• Often used as a source of heat
• Red lamps in cafeterias keep food warm
with infrared radiation
ELECTROMAGNETIC
SPECTRUM
• Other uses include:
• Controlling televisions through a remote
control
• Reading CDs via a computer or game
console
ELECTROMAGNETIC
SPECTRUM
• Detecting trapped victims or heat loss in a
building through a thermogram
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• Visible Light
• The range of electromagnetic waves that
you can detect with your eyes
ELECTROMAGNETIC
SPECTRUM
• Each wavelength in the visible spectrum
corresponds to a specific frequency and
has a particular color
• These range from long-wavelength red
to short-wavelength violet
ELECTROMAGNETIC
SPECTRUM
• If all the colors are present, you see the light as
white
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• Ultraviolet Waves
• Wavelengths vary from 400 nm to 4 nm
ELECTROMAGNETIC
SPECTRUM
• Ultraviolet waves are energetic enough to
enter skin cells
• Overexposure can cause skin damage
and cancer
ELECTROMAGNETIC
SPECTRUM
• Some ultraviolet waves are helpful
• Exposure allows the body to create
vitamin D, which is needed for bones
and teeth to absorb calcium
ELECTROMAGNETIC
SPECTRUM
• Also have the ability to kill bacteria on
food or medical supplies
• Can make some materials fluoresce –
absorbs the UV rays and reemits the
energy as visible light
ELECTROMAGNETIC
SPECTRUM
• This is used by CSI technicians when
looking for fingerprints or blood at a
crime scene
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM
• X-Rays
• Very short wavelengths ranging from
12 nm to 0.005 nm
ELECTROMAGNETIC
SPECTRUM
• Have high energy and can penetrate
matter that light cannot
ELECTROMAGNETIC
SPECTRUM
• Often used in medicine, industry, and
transportation to make pictures of the
inside of solid objects
ELECTROMAGNETIC
SPECTRUM
• Gamma Rays
• Have the shortest wavelength in the
electromagnetic spectrum at about 0.005
nm or less
ELECTROMAGNETIC
SPECTRUM
• Have the highest frequency and
therefore the most energy and greatest
penetrating ability of all the
electromagnetic waves
ELECTROMAGNETIC
SPECTRUM
• Exposure to small amounts of gamma rays are
tolerable, but overexposure can be deadly
ELECTROMAGNETIC
SPECTRUM
• Used in the medical field to kill cancer cells
and make pictures of the brain based on
brain activity
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC
SPECTRUM