Waves Carry Energy, not Matter
• A wave is a repeating disturbance that
transfers energy through matter or space.
• Waves carry energy from one place to another.
• When waves travel through solids, liquids,
and gases, matter is not carried along with
the waves.
• Waves carry energy without transporting
matter.
Types of Waves
• All waves are produced by something
moving back and forth, or vibrating.
• It is the energy of the vibrating object that
waves carry outward.
• Some waves, known as mechanical waves,
can travel only through matter.
• The material through which a wave travels is
called the medium .
• Waves called electromagnetic waves can
travel either through matter or through empty
space.
Transverse Waves
• A transverse wave causes particles in matter
to move back and forth at right angles to the
direction in which the wave travels.
• High points in the
wave are called
crests. Low points
are called troughs.
• The series of crests
and troughs forms a
transverse wave.
Compressional Waves
• Another type of mechanical wave is a
compressional wave.
• A compressional wave causes particles in
matter to move back and forth along the
same direction in which the wave travels.
Compressional Waves
• The places
where the coils
are squeezed
together are
called
compressions
• The places where the coils are spread
apart are called rarefactions. The series
of compressions and rarefactions forms
a compressional wave.
Waves
1
Combination Waves
• Seismic waves move through the ground
during an earthquake.
• Some of these waves are compressional,
and others are transverse.
• The seismic
waves that cause
most damage to
buildings are a
kind of rolling
waves.
Electromagnetic Waves
• Light, radio waves, and X rays are examples
of electromagnetic waves.
• Electromagnetic waves are transverse waves.
• They contain electric and magnetic parts that
vibrate up and down perpendicular to the
direction the wave travels.
Properties of Waves
• The properties that waves have depend on
the vibrations that produce the waves.
• For example, if you move a pencil slowly
up and down in a bowl of water, the waves
produced by the pencil’s motion will be
small and spread apart.
Wavelength
• The distance between one point on a wave
and the nearest point moving with the same
speed and direction is the wavelength.
• The wavelength
of a transverse
wave is the
distance between
two adjacent
crests or two
adjacent troughs.
Wavelength
• The wavelength of a compressional wave
is the distance between two adjacent
compressions or rarefactions.
Frequency
• The frequency of a wave is the number
of wavelengths that pass by a point each
second.
• If you were watching a transverse wave
on a rope, the frequency of the wave
would be the number of crests or troughs
that pass you each second.
Period and Frequency (P297)
• Frequency (f) of a wave is the number of
wavelengths that pass a fixed point each
second.
• SI Unit is hertz (Hz) 1 Hz = 1 wave/sec
• Period (T) of a wave is the amount of time
it takes one wavelength to pass a point
• SI Unit is sec/wavelength
• f= 1/T and T= 1/f
Amplitude of a Transverse Wave
• The amplitude of a transverse wave is half
the distance between a crest and trough.
• As the distance between crests and troughs
increases, the amplitude of a transverse
wave increases.
Amplitude of a
Compressional Wave
• The amplitude of
a compressional
wave depends on
the density of
material in
compressions
and rarefactions.
Amplitude and Energy
• The vibrations that produce a wave transfers
energy to the wave.
• The more energy a wave carries, the larger
its amplitude.
• Amplitude of waves relate to the energy of the
wave.
Review- Nature of Waves
• Wave- a repeating disturbance or movement
that transfers energy through matter or space.
– Molecules pass energy on to other molecules
– Waves carry energy without transporting matter
– All waves are produced by something vibrating
– Medium – a material through which a wave travels
• Mechanical Waves
– Travel only through matter
– Transverse waves matter moves perpendicular to
direction wave moves- wave in a string or slinky
– Compressional waves matter moves in the same
direction that the wave moves.- sound waves
Review- Wave Properties
• Waves differ– How much energy they carry
– How fast they travel
– How they look
– Transverse waves have crests and troughs
– Compressional waves have dense regions
called compressions and less dense regions
called rarefaction
Wave Properties
• Wave length- the distance between one point
in the wave and the next corresponding part
• Frequency- how many waves pass a fixed
point each second
– Expressed in hertz
– As frequency increases, wavelength decreases
– The frequency of a wave equals the rate of
vibration of the source that creates it.
Wave Properties
Wave Speed
• The speed of a wave depends on the medium
in which the wave travels.
• You can calculate the speed of a wave if you
know its wavelength and frequency using
this equation.
• Wave Speed Equation
wave speed (m/s) = wavelength (m) X frequency (Hz)
v= λf
Wave Speed
• In this equation, v is the symbol for wave
speed and f is the symbol for frequency.
• The SI unit for frequency is the hertz,
abbreviated Hz. One hertz equals one
vibration per second, or one wavelength
passing a point in one second.
• The wavelength is represented by the Greek
letter lambda, λ, and is measured in meters.
Problems P299
• Example: What is the speed of a sound
wave that has a wavelength of 2.00m and
a frequency of 170.5 Hz?
• V= fλ
• Assignment Page 299: 1-4
Amplitude
• Amplitude is a measure of the energy in a
wave
– The more energy a wave carries, the greater the
amplitude.
– Amplitude of compressional waves is related to
how tightly the medium is pushed together at the
compression.
– The more dense the compression, the larger the
amplitude is and the more energy the wave
carries.
– The less dense the rarefactions, the higher the
amplitude and the more energy the wave carries
Amplitude of transverse waves
• The distance from the crest or trough of a
wave the rest point of the medium.
• Example: how high an ocean wave
appears above the water level.
Waves Can Change Direction or
Amplitude (p 304-306)
• Waves don’t always travel in the same
straight line.
• Waves can change direction when they
travel from one material to another or when
they strike some media.
• All waves can reflect (bounce off a surface),
refract (change direction), or diffract (bend
around an obstacle).
• Waves can also change amplitude when they
pass through another wave, this is referred to
as interference.
The Law of Reflection
• According to law of reflection, the angle that the
incoming wave (incident) makes with the normal
equals the angle that the outgoing (reflection)
wave makes with the normal.
Incident angle= Reflection angle
θi
θr
θi=θr
Refraction
• When a light wave
moves from air to
water, it slows
down.
• This change in
speed causes the
light wave to bend.
• Refraction is the change in direction of a
wave caused by a change in its speed as it
movers from one material to another.
Refraction
• The greater the change in speed is, the
more the wave bends.
• When a wave passes into a material that
slows it down, the wave is bent toward the
normal.
• When a wave passes into a material that
speeds it up, the wave is bent away from
the normal.
Diffraction
• Waves can change direction by diffraction,
which is the bending of waves around an
object.
• The amount of diffraction or bending of the
wave depends on the size of the obstacle the
wave encounters.
• If the size of the obstacle is much larger than
the wavelength, very little diffraction occurs.
• If the size of the obstacle is much smaller
than the wavelength, the wave diffracts a lot.
Diffraction of Sound and Light
• The wavelengths of sound waves are
similar to the size of objects around you,
but the wavelengths of light waves are
much shorter.
• As a result, you can hear people talking
in a room with an open door even though
you can’t see them.
Interference
• Waves can also change amplitude when
they pass through another wave, this is
referred to as interference.
• Interference is the ability of two or more
waves to combine and form a new wave.
• Waves pass right through each other and
continue in their original direction.
• New wave exists only while the two
original waves continue to overlap.
Interference
Superposition Principle
Constructive Interference
In Phase
½λ
Destructive Interference
Out of Phase
Standing Waves
(p310,334)
• Standing wave- a special type of wave pattern
that forms when waves of equal wavelength and
amplitude, but traveling in opposite directions,
continuously interfere with each other. Standing
waves form a pattern that stays in one place.
• Node – the place where two waves always
cancel each other.
• Fundamental frequency the main tone that is
heard when something vibrates.
• Overtone is a vibration whose frequency is a
multiple of the fundamental frequency.
Resonance (p311)
• Resonance is the process by which an
object is make to vibrate by absorbing
energy at its natural frequency.
• Resonance is the ability of an object to
vibrate by absorbing energy at its natural
frequency.
Waves Carry Energy, not Matter
• A wave is a repeating disturbance that
transfers energy through matter or space.
• Waves carry energy from one place to another.
• In water waves, the energy is transferred by
water molecules.
• When waves travel through solids, liquids,
and gases, matter is not carried along with
the waves.
• Waves carry energy without transporting
matter.
Assignments Chapter 10
• Page 299: 1-2-3-4
• Chapter Review Page 316-317:9-18*, 2728-29
• Notetaking Worksheet
Types of Waves
• All waves are produced by something
moving back and forth, or vibrating.
• It is the energy of the vibrating object that
waves carry outward.
• Some waves, known as mechanical waves,
can travel only through matter.
• The material through which a wave travels is
called the medium .
• Waves called electromagnetic waves can
travel either through matter or through empty
space.
Amplitude of a Transverse Wave
• The amplitude of a transverse wave is half
the distance between a crest and trough.
• As the distance between crests and troughs
increases, the amplitude of a transverse
wave increases.
Wave Speed
• The speed of a wave depends on the medium
in which the wave travels.
• You can calculate the speed of a wave if you
know its wavelength and frequency using
this equation.
• Wave Speed Equation
wave speed (m/s) = wavelength (m) X frequency (Hz)
v= λf
Waves Can Change Direction or
Amplitude (p 304-306)
• Waves don’t always travel in a straight line.
• Waves can change direction when they
travel from one material to another or when
they strike some media.
• All waves can reflect (bounce off a surface),
refract (change direction), or diffract (bend
around an obstacle).
• Waves can also change amplitude when they
pass through another wave, this is referred to
as interference.
Making Sound Waves
• Vibrations transfer
energy to nearby air
particles, producing
sound waves in air.
• Every sound you
hear is caused by
something vibrating.
For example, when you talk, tissues in your
throat vibrate in different ways to form sounds.
Sound Waves are
Compressional Waves
• Sound waves are formed when a vibrating
object collides with air molecules,
transferring energy to them.
• Sound waves produced by a vibrating object
are compressional waves.
• A vibrating drum head
produces a sound wave.
• The drum head produces
a compression each time
it moves upward and a
rarefaction each time it
moves downward.
Sound Waves are
Compressional Waves
• Sound waves can only travel through matter.
• Medium- the type of matter whether liquid,
solid or gas; that sound waves travel through.
• The energy carried by a sound wave is
transferred by the collisions between the
particles in the material the wave is
traveling in.
The Speed of Sound
• A sound wave’s speed
depends on the medium
through which it travels.
• Sound waves travel more
quickly through solids and
liquids because the
molecules are closer
together than in a gas.
• The speed of sound through
a material increases as the
temperature of the material
increases.
Problems (d=vt)
• A cannon flash is seen, but it takes 6 seconds for the
sound to reach the persons ear. How far away was the
cannon?
• A ship 1200 meters off shore fires a gun. How long after
the gun is fired will it be heard on the shore?
• A drummer hits a cymbal and 10 seconds later hears the
echo of the sound from a distant mountain. How far
away was the mountain?
Perception and
Physical Measurement
The human ear interprets the physical
characteristics of the sound waves.
The Loudness of Sound
• What makes a sound loud or soft?
• The difference is the amount of energy.
• Loud sounds have more energy than
soft sounds.
• The amount of energy a wave carries
corresponds to its amplitude which is
related to the density of the particles in
the compressions and rarefactions.
Intensity
• The amount of energy that a wave carries past a
certain area each second is the intensity of the
sound.
• The intensity of sound
waves is related to the
amplitude. Loudness is
the human perception of
sound intensity.
This figure shows how the
intensity of sound from
the cymbals decreases
with distance.
The Decibel Scale and Loudness
• The intensity
of sound
waves is
measured in
units of
decibels (dB).
• The softest sound a person can hear has an
intensity of 0 dB.
• Sound with intensities of about 120 dB or
higher are painful to people.
The Decibel Scale and Loudness
• Loudness is the human perception of the
intensity of sound waves.
• Each increase of 10 dB in intensity
multiplies the energy of the sound waves
ten times, 20 dB multiplies by 100, 30 dB
by 1000 times.
• Most people perceive this as a doubling
of the loudness of the sound.
Sound Intensity
Decibels
Sound
Whisper
Normal Conversation
Noisy Office
Safe Limit
Rock Concert
Jet engine taking off
TJCA Lunchroom
Intensity
15
60
80
90 Ear damage
120
150
200
Frequency and Pitch
• The frequency of sound waves is determined by the
frequency of the vibrations that produce the sound.
Frequency is the number of compressions or
rarefactions of a sound wave that passes per second,
• People are usually able to hear sounds with
frequencies between about 20 Hz and 20,000 Hz.
• Pitch is the human perception of the frequency of
sound, how low or high a sound seems to be..
• Sounds with low frequencies have low pitch and
sounds with high frequencies have high pitch.
Ultrasonic
• Ultrasonic waves are sound frequencies
over 20,000 Hz.
• Ultrasonic waves have medical and
scientific uses.
• Infrasonic or subsonic waves with
frequencies below 20 Hz usually can’t be
heard but may feel a rumble.
Doppler Effect
• The change in pitch or wave frequency
due to a moving wave source is called the
Doppler Effect.
• See page 331
Doppler Effect
Sounds moving toward a listener rise in pitch while
sounds moving away from a listener lower in pitch.
V=f λ
λ
f
λ
f
The Reflection of Sound
• Echoes are sounds that reflect off surfaces.
• Repeated echoes are called reverberation.
• The reflection of sound can be used to locate
or identify objects.
• Echolocation is the process of locating objects
by bouncing sounds off them. (Sonar)
Echo
• Distance from source
– Persistence of human ear 1/10 second
– Speed of sound 340 m/s
– Distance =
• Wavelength of sound less than height of
reflecting body
• Intensity of the sound sufficient to be
heard after the reflection
Noise vs Music
• Music is pleasant to the ear
• Regular patterns
• No sudden changes in
– loudness
– frequency
– wavelength
Sound Summary
• Sound is produced by the vibration of some
object
– drum head
– String
– metal tuning fork
– column of air
• Sound travels by waves but only in matter
• Sound waves are compressional waves
• Speed of Sound
– Sound travels only in matter
– Sound travels fastest in solids, slowest in gases
– Sound travels faster at higher temperatures
Sound Summary
• Amplitude of Sound Waves
–
–
–
–
Amplitude is a measure of the energy of the wave
Intensity is the energy divided by the area
Intensity is measured in decibels
The human ear can safely hear sounds with intensity
between 0 db and about 120 db
– Loudness is how the human ear perceives intensity
• Frequency of Sound Waves
– Frequency is vibrations per second (Hz)
– Pitch is how the human ear perceives frequency
– The human ear can detect sounds between 20 Hz and
20,000 Hz
Waves in Empty Space
• Light from the Moon has
traveled through space that
contains almost no matter.
• You can see light from the
moon, distant stars, and
galaxies because light is
an electromagnetic wave.
Electromagnetic Waves
• Light, radio waves, and X rays are examples
of electromagnetic waves.
• Electromagnetic waves can travel through
space or through matter.
• Electromagnetic waves are transverse waves.
• They contain electric and magnetic parts that
vibrate up and down perpendicular to the
direction the wave travels.
Producing Electromagnetic
Waves
• Magnetic waves are made by vibrating
electric charges.
• Electric and magnetic fields are related
forces that operate even in empty space.
– A moving electric charge produces a
magnetic field
– A changing magnetic field creates an electric
field.
Producing EM Waves (cont)
• Electromagnetic waves are produced
when an electric charge is vibrating.
– Vibrating electric charges are surrounded by
vibrating electric and magnetic fields.
– Vibrating electric and magnetic fields travel
outward from the moving charge.
Properties of Light Waves
• An electromagnetic wave contains an electric
part and a magnetic part.
• Both parts are called fields and vibrate at
right angles to the wave motion.
EM waves are transverse waves
• EM waves carry radiant energy
• EM waves are characterized by frequency,
wavelength and velocity.
• V= λ f
• Speed of light is a constant in any medium
• As frequency increases, wavelength decreases
– Frequency is the number of vibrations per second
– Wavelength is the distance between crests
The Speed of Light
• In empty space (vacuum), light travels at a
speed of about 300,000 km/s.
• Light travels so fast that light emitted from
the Sun travels 150 million km to Earth in
only about eight and a half minutes.
• When light travels in matter, it interacts
with the atoms and molecules in the
material and slows down.
• As a result, light travels fastest in empty
space, and travels slowest in solids.
Wavelength and
Frequency of Light
• Wavelengths of light are usually expressed
in units of nanometers (nm).
• One nanometer is equal to one billionth of
a meter.
• Green light has a wavelength of about 500
nm, or 500 billionths of a meter. A light
wave with this wavelength has a frequency
of 600 trillion Hz.
Intensity of Light Waves
• The intensity of waves is a measure of the
amount of energy that the waves carry.
• For light waves, the intensity determines
the brightness of the light.
• A dim light has lower intensity because the
waves carry less energy.
The Electromagnetic Spectrum
• The electromagnetic spectrum is the
complete range of electromagnetic wave
frequencies and wavelengths.
The Electromagnetic Spectrum
• At the other end of the spectrum the waves
have high frequency, short wavelength, and
high energy.
The Electromagnetic Spectrum
• At one end of the spectrum the waves have low
frequency, long wavelength, and low energy. At
the other end the waves have high frequency,
high energy and short wavelengths.
Long Wavelength
Low Frequency
Low Energy
Short Wavelength
High Frequency
High Energy
Speed, Wavelength,
Frequency
• Speed = frequency x wavelength
• V= f λ
• frequency increases- wavelength decreases
• frequency decreases- wavelength increases
Radio Waves and Microwaves
• The wavelengths of radio waves are greater
than about 0.3 meters.
• Some are even thousands of meters long.
• The shortest radio waves are called
microwaves.
• These waves have a wavelength between
about 0.3 meters and 0.001 meters.
Infrared Waves
Infrared waves have wavelengths between
0.001 meters and 700 billionths of a meter.
• All warm bodies emit infrared waves.
• Law enforcement officials and military
personnel sometimes use special night
goggles that are sensitive to infrared waves.
These goggles can be used to help locate
people in the dark.
Visible Light and Color
• The range of electromagnetic waves between
700 and 400
billionths of a
meter is the
range of
wavelengths
people can see.
Ultraviolet Waves
• Electromagnetic waves with wavelengths
between about 400 billionths and 10
billionths of a meter are ultraviolet waves.
• Ultraviolet waves carry more energy than
visible light waves.
• Sunlight that reaches Earth’s surface contains
a small fraction of ultraviolet waves.
X Rays and Gamma Rays
• The electromagnetic
waves with the highest
energy, highest
frequency, and shortest
wavelengths are X rays
and gamma rays.
• X rays pass through soft
tissues, but are blocked
by denser body parts,
such as bones.
X Rays and Gamma Rays
• Gamma rays are even more energetic
than X rays.
• One use of gamma rays is in the food
industry to kill bacteria that might
increase the rate of spoilage of food.
Electromagnetic Waves
from the Sun
• Most of the
energy emitted
by the Sun is
in the form of
ultraviolet,
visible, and
infrared waves.
• Only a tiny fraction of this energy
reaches Earth.
Schedule
Topic
Tue 2/1
Waves, Wave Measurements
Wed 2/2 Wave behavior
Thur 2/3 Wave behaviorsuperposition
Fri 2/4
Chapter 10 Review
Mon 2/7 Sound waves
Tue 2/8
Chapter 11 Review
Wed 2/9 Electromagnetic waves
Thur 2/10 Electromagnetic Spectrum
Fri 2/11
Light
Mon 2/14 Optics Lab
Tue 2/15 Review
Wed 2/16 Test
Thur 2/17
Assignment
Read p290-295 Worksheet Section 1&2,
Read p 296-307, Problems P299
Read p 308-311 Complete Note taking worksheet
Ch 10 Review Page 316:9-16, 17, 27-29
Read p322-332, Sound worksheet
Page 348: 8-17
Read p354-364, EM waves worksheets
Read p384-388
Read p 389-393, Light worksheet
Complete lab and all worksheets
Mirrors and Lens NTWS
Turn in all Homework
Seeing is Reflecting
Page 384
• To see an object:
– It must produce light
– Or Reflect light
• All objects
– Reflect light
– Absorb light
• Some Transmit light (refract)
Matter and Light
• Absorb, Reflect, Refract (transmit)
• Materials that absorb and reflect light are
called opaque.
• Materials that refract and absorb light
irregularly are called translucent.
Translucent materials allow some light to
pass through.
• Materials that refract (transmit) most of the
light are called transparent.
Reflected Light
Page 385
• Reflection- a light wave strikes an object
and bounces off.
• Angle of reflection = angle of incidence
• Regular Reflection – mirrors – reflect light
in single direction and form sharp images.
• Diffuse Reflection- irregular surfaces like
brick walls reflect light in many different
directions and do not form an image.
• We see objects because they reflect light.
Refracted Light
Page 386-387
• Refraction- change in speed of a light wave
when it passes from one material into another.
• Light rays are bent as they pass from one
material into another.
• Index of Refraction- indicates how much a
material reduces the speed of light;
• The more light is slowed, the higher the index of
refraction.
Refraction
• In prisms and rain drops, the different colors
(wavelengths) are bent different amounts.
• Prisms separate light into visible spectrum
based on wavelengths.
• Rainbows are cause by water droplets
refracting wavelengths of sunlight.
• The bending separates the colors into the
spectrum (red, orange, yellow, green, blue,
indigo, violet)
• Refraction of light through air layers can
produce a mirage
Color (Page 389)
• When white light (mix of all colors) falls on
an object, some colors are absorbed,
some are reflected.
• We see objects in the color that is
reflected by the object.
• The other colors are absorbed.
• The colors that are absorbed or reflected
depend on the material.
Light and Color (Page 389)
• Color is determined by the wavelength of
the light the object reflects.
• Objects appear to be white if they reflect
all colors of visible light.
• Objects appear to be black if they absorb,
rather than reflect, all colors of light.
Filters and Pigments
• Filter- a transparent material that absorbs all
colors except the color or colors it transmits.
• Filters can make objects appear to be different
colors.
• A pigment is a colored material that is used to
change the color of other substances.
• The color of the pigment is determined by the
wavelength of the light reflected.
Mixing Color (p 392-393)
• Mix all of the colors of light and get white
light.
• Mix all the colors of pigments and get
black since a mixture of all the colors of
pigment absorb all the colors and do not
reflect any, the object appears black.