Waves, Light, and
Sound
Teacher Domain:
Waves
http://www.teachersdomain.org/resou
rce/lsps07.sci.phys.energy.waves/
Waves Notes
1) Two Major Types
A. Mechanical - must travel through a
medium (water, sound)
B. Electromagnetic - no medium required, can
travel through a vacuum (light, UV, radio,
gamma rays)
Mechanical waves
Transverse waves - medium travels at a
right angle to the direction of the wave
Parts of a Mechanical
Transverse Wave
Crest – highest point of a wave
 Trough – lowest point of a wave
 Wave Height – vertical distance
between the crest and the trough
 Wavelength – horizontal distance
between two crests or two troughs
 Amplitude is the distance from the
baseline to the top of the crest or
bottom of the trough.

Wave Parts
http://www.teachersdomain.org/resou
rce/lsps07.sci.phys.energy.amplitude
/
Mechanical waves
Compressional waves - medium travels in the same
direction as the wave.
Frequency - the number of waves to pass a
point in a given period of time. Can be
calculated as
f = # of waves (cycles) / t
f - frequency
t - time
units
Hertz (Hz)
(cycles)/ second
second
Wave measurements
Period - how long it takes one wave to pass a
point. Can be calculated as
T= 1/f
T - period
f - frequency
units
seconds
Hertz (Hz)
(cycles)/ second
Flash card
T=
1
f
1
T
f
Period
Units
T - period
sec, min
f - frequency
hertz
Flash card
# of waves
f=
t
#
of
waves
f
t
Frequency
Units
f - frequency
hertz
# of waves
cycles
t - time
sec, min
Wavelength - length of one wave cycle (wave
cycle is a crest and a trough or one compression
and one rarefaction). Can be calculated as
λ = total distance (d) / # of waves
units
λ – wavelength m, mm, nm, pm, μm
d – distance
m, mm, nm, pm, μm
Flash card
d

# of waves
d
of
 #
waves
Wavelength
 - wavelength
d - total distance
# of waves
Units
m, cm, nm
m, cm, nm
cycles
Wave velocity – how fast a wave travels. Can be
calculated as
v=λf
units
v – velocity
m/sec, μm/sec
λ – wavelength μm, m, mm, nm, pm
f – frequency
Hertz (Hz) = /sec
NOTE: There are no set units for velocity or
wavelength
Flash card
v= f
v

f
Wave velocity
v - velocity
Units
cm/sec, m/sec, nm/sec
f - frequency
hertz
 - wavelength
cm, m, nm
Brain Pop: Waves

http://glencoe.mcgrawhill.com/sites/0078802482/student_vie
w0/brainpop_movies.html#
Example
If an earthquake’s p-wave travels at 5600
m/sec with a wavelength of 372 m, what is
the frequency of the wave?
v = 5600 m/sec
f=?
λ = 372 m
v=λ f
f=v/λ
f = 5600 m/sec / 372 m
= 15.05 /sec = 15.05 Hz
WAVE PRACTICE
PROBLEMS
It takes 2 seconds for this wave to go this
distance.
1. What is the period of this wave?
2. What is the frequency of this wave?
3. What is the wavelength of this wave?
4. What is the speed of this wave?
Teacher Domain
Video: What is
Sound?
http://www.teachersdomain.org/resou
rce/phy03.sci.phys.howmove.collage
/
5. 2 waves leave the same point at the same time.
They both travel 30 m. The first wave takes 30
seconds, what is its velocity? The second wave
takes 180 seconds, what is its velocity?
6. What is the frequency of a 990 m/sec wave
that has a wavelength of 30 m?
The speed of a wave depends on the medium and
temperature.

Liquids conduct sound better than gases. Solids
conduct sound better than liquids. This is due to
how close the particles are to each other.

In air, the speed of sound is 344 m/sec at 20 ºC,
but only 332 m/sec at 0ºC. This is due to the
particles moving faster at higher temperatures.
How high or low the frequency of a sound is, is
the pitch of the sound. The average human
hearing range is 20 Hz to 20000 Hz.
Sounds higher than 20000 Hz are ultrasonic.
 Sounds lower than 20 Hz are subsonic or
infrasonic.


Loudness of a sound depends on the person
hearing it.

Loudness is related to the intensity of the
sound.

The higher the intensity, the louder the
sound.
The intensity of a sound is determined by the
amount of energy in a wave.

Therefore, the higher the amplitude the
higher the intensity.

Intensity level for a sound is measured in
decibels (dB).

At 120 dB, a sound causes pain and
permanent hearing loss.
Intensities of Some Sounds
Lawn mower
Chain Saw
Jet taking off
Cat purring
100 dB
115 dB
150 dB
25 dB
Sound: Pitch and
Intensity
http://www.teachersdomain.org/resou
rce/hew06.sci.phys.energy.sound/
Doppler Effect
Doppler effect results in higher and lower
sound/light intensity as an object move
toward/away from us.
Approaching sounds get louder. Retreating
sounds get quieter.
Approaching lights get brighter. Retreating
lights get dimmer.
Teacher Domain:
Video Doppler
http://www.teachersdomain.org/resou
rce/phy03.sci.phys.energy.doppler/
Doppler Effect
http://glencoe.mcgrawhill.com/sites/0078807220/student_vi
ew0/chapter15/concepts_in_motion.
html
Types of sounds
1.
White noise – all waves
have the same amplitude
but different frequencies –
it is calming.
2. Noise – no set pattern or
definite pitch – it is
unpleasant/irritating.
3. Music – definite pattern
using special pitches and
sound quality.
THE MAKING OF SOUND
1. resonance – making an
object vibrate at its natural
frequency
Overtones – when each half of a string vibrates
on its own

The number of overtones produced
determines the quality of sound.

Each overtone is a multiple of the
fundamental frequency
•
•
•
1st overtone
2nd overtone
3rd overtone
2 X FF
3 X FF
4 X FF
6. notes – there are 8 notes in music each
with its own frequency
7. The frequency range for a note is an
octave.
8. The highest note in an octave is 2X the
frequency of the lowest note.
Wave Interferences
1.
interference – combining of 2 or
more waves to make a new
wave
2.
constructive –
compressions/crest arrives
together and combine → greater
compression/crest amplitude ↑
→ loudness↑
3.
destructive – compression
arrives with rarefaction → less
compression or canceling of the
wave amplitude ↓ or 0 →
loudness ↓ or 0
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concepts_in_motion.html
Reverberation
echoes
Electromagnetic waves

Waves that form the electromagnetic spectrum
have characteristics of both waves and particles.

These are transverse waves.

The waves can travel through empty space.

Energy is transferred by radiation.
Teacher Domain:
Electromagnetic
Waves
http://www.teachersdomain.org/resou
rce/phy03.sci.phys.energy.emspectru
m/
Teacher Domain:
Electromagnetic
Waves
http://www.teachersdomain.org/resou
rce/phy03.sci.phys.energy.nasaspect
rum/

Produced by electrically charged particles.

This is electromagnetic radiation.

In a vacuum, all waves have the same velocity,
even though they have different frequencies and
wavelengths.

The radiation has momentum because it is
particle-like and travels in bundles called photons.
THE
ELECTROMAGNETIC
SPECTRUM
A. Radio waves
Composed of AM radio, FM radio, shortwave radio, TV,
radar, and microwaves.
 Have the longest wavelength and lowest frequency.
 Sound and images are transmitted by modulation –
varying of amplitudes and frequencies – this process is
used by radio, tv, cellular phones, and cordless phones.
 Microwaves are used for communication and cooking.

These have the highest frequency and energy.
B. Infrared
Longer wavelength than visible but
shorter wavelength than radio waves.
 Used to measure the amount of heat
given off by an object.




Uses for IR radiation
Medicine can use it to detect tumors which are areas of
higher heat than the rest of the body
Construction – to determine areas of a house that needs
more insulation (areas of greatest heat loss)
Security – to set-up alarm systems and trigger alarms.
Military – Night vision and heat sensing equipment to find
targets and individuals or shelter
Teacher Domain
Video: IR
http://www.teachersdomain.org/resou
rce/ess05.sci.ess.earthsys.infrared/
C. Visible
The light we see. Very small
portion of the spectrum.

Broken into 7 bands of color.

Used to cause chemical
reactions. Energy source for
photosynthesis.
Teacher Domain:
Video Light
http://www.teachersdomain.org/resou
rce/lsps07.sci.phys.energy.lightcolor/
D. Ultraviolet
Shorter wavelength than visible.

Our body uses it to make Vitamin D.

Blocked to a degree by the ozone
(O3) layer of the atmosphere.
Sunglasses and sunscreen can block
its rays.

Uses:
Destroy bacteria, viruses and sterilize
materials (including water)
 Detect fluorescence. (stamps at an
amusement park)


Side effects:
Overexposure can kill healthy cells
 Prolonged and frequent exposures and lead
to sagging, dry skin and in some cases skin
cancer.

E. X-rays
Shorter wavelength than UV and higher frequency
with higher energy and greater penetrating power.

Can travel through several types of matter (skin,
muscle, suitcases)

Absorbed by dense materials

Contained within lead container

Uses
X-ray pictures of bones and body tissue for
diagnosis.
 X-rays of luggage to reduce searches


Side effects:
Loss of hair, fatigue, and nausea due to
prolonged exposure
 Destruction of body tissue
 Burns

F. Gamma rays
Shortest wavelength, highest frequency, most energy of any
wave.


Can penetrate most materials
Uses:


Radiation treatment for cancer or destroy a group of cells
Side effects:



Major exposure – death
Moderate exposure – cancer
Prolonged exposure – loss of hair, fatigue and nausea
VISIBLE LIGHT

Materials are classified according to how light
passes through them.
Opaque materials block all light and allow no light
to pass through. This light can be reflected or
absorbed by the material
 Transparent materials allow light to pass through
and objects can be seen clearly.
 Translucent materials allow some light to pass
through but objects can not be seen clearly

Colors Reflect and Absorb of Light

Colors are perceived by the absorption
and reflection of light
Blue objects reflect blue light.
 White objects reflect all light.
 Black objects absorb all light.

Light Colors
The primary colors of light
are green, blue and red.

When primary color of
light are combined, white
light is produced. These
are additive colors.
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on.html
Pigment Colors

Pigments are colored
materials that absorb
some colors and reflect
others.


3 primary pigment colors
are magenta (red), cyan
(blue), and yellow
When primary color
pigments are combined
the pigments make black.
These are subtractive
colors.
THE HUMAN EYE AND SIGHT

Our eye picks-up dim light and movement in the rod
cells in the back of our eye.

The cone cells pick-up color and brightness. They are
specialized to pick-up certain colors.




Red cones pick-up red and yellow light.
Blue cones pick-up blue and violet light.
Green cones pick-up green and yellow light.
Cones and rods pick-up the information of what has
stimulated them and pass it to the brain along the optic
nerve.
Color Blindness
Some people, mostly males, experience color
blindness.
 This is an inherited trait usually passed through
the mother (x-chromosome trait).
 A person will not be able to distinguish one or
more color.
Usually reds and greens.
 Some have trouble with blue.

PROPERTIES OF LIGHT
Light like all electromagnetic radiation acts like
a wave when it bounces and bends.
1.
Reflection occurs when light strikes an
object and bounces off.




Incoming light is the incident beam
The bounced off light is the reflected beam
Smooth surfaces reflect light in one
direction, giving an image. While rough
surfaces reflect light in many directions and
do not give an image.
Law of reflection states that the angle of
incidence is equal to the angle of reflection.
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Incoming light
i
normal
r
i = angle of incidence
r = angle of reflection
Reflected light
Smooth surface

Refraction occurs
when light passes
from one medium to
another and the angle
of the light waves is
bent.

The bending is
caused by a change
in the speed of the
light waves.
http://glencoe.mcgrawhill.com/sites/0078807220/
student_view0/chapter18/c
oncepts_in_motion.html

Diffraction occurs when the wave bends to
go around a barrier.


Diffraction occurs in sound, water, and
electromagnetic waves.
Diffracting grating are a series of slits that
can bend light and separate it into its colors.

Interference also occurs in light waves
when crests combine – bright bands
form.
When a crest and a trough combine –
dark bands form.
Additional Facts

Scattered light is redirected in all directions

When particles of dust scatter blue light, the sky
appears blue.

Yellow light is produced when red and green overlap

Cyan pigment will be used to produce blue and greens.
While magenta pigment will be used to produce orange
and purples.

Ultraviolet light can be seen by bees but not
by humans.

During sunset and sunrise orange light is
scattered giving the sky an orange-cast.

Light is absorbed by the retina of the eye.
Mirrors
Plane mirrors have a reflective coating
on the back of a flat piece of glass.

Produce virtual images.

Images that have no light rays
passing through them and appear to
come from behind the mirror.
Concave mirrors curve inward and can reflect in three
ways.
1. If the object is placed beyond the focal point of the
mirror, an upside down, enlarged, real image will
appear.
2. If the object is placed on the focal point, no image is
produced.
3. If the object is placed between the focal point and the
mirror, an upright, enlarged, virtual image is produced.

Convex mirrors curve outward and produce small,
virtual images.

For all mirrors:





Optical axis is a straight line drawn through the center
of the mirror
Focal point is the place on the optical axis where the
parallel lines of reflection meet.
Focal length is the distance from the focal point to the
center of the mirror.
Virtual images have no light rays passing through
them.
Real images are produced by reflected light rays.
Lenses
Convex lens are thick in the middle and thin on the
edges
 These lenses refract light to a focal point and an
image can be projected.
 These lenses can produce real or virtual, enlarged
or reduced, or upright or inverted images according
to the location of the object.
 Used to correct farsightness.
Concave lens are thinner in the middle and
thicker at the edges.
 These lenses refract light toward the edges.
 These lenses never produce a real image.
 Image is virtual, upright and reduced.
 Used to correct nearsightness.
Optical Instruments
Aid the human eye to make observations
1. Telescopes – view faraway objects
2. Refracting telescope



Use 2 convex lens
Due to size of lenses, images can be
distorted if it sags
Lenses are very heavy and costly to make
3.
Reflecting telescope

4.
Use a concave mirror, plane mirror and a convex lens
Binoculars

A refracting telescope with 2 lenses for each eye and a
reflecting prism to invert the image so we see an upright
image.
NOTE: Not all radiation passes through our atmosphere,
therefore, to get a clear image of what is in space we
send telescopes above our atmosphere. These
telescope pick-up UV, IR, x-rays, and visible light.
5. Microscope
 2 convex lens used to magnify small
objects.
 1st lens produces an enlarged real
image that the 2nd lens enlarges
and changes into a virtual image.
6. Cameras
 Lenses gather light and project an image on
light-sensitive film.
 The shutter controls the amount of light that
enters the aperture.
 The image produced is real and inverted
but smaller than the object.

Wide-angle lenses
produce small image that includes much of
the surroundings
 have short focal length


Telephoto lenses
have long focal length
 protrude from the camera bringing the image
closer to the camera

Polarized light
All light waves vibrate in one plane.

Some 3D images can be produced using
polarized filters that are aligned at 90º angle
to each other. Two projectors with filters are
used to produce the image on the screen.

Polarizing filters can be used on cameras to
reduce glare.
Lasers
Use coherent light – all crest and troughs are aligned and
travel in the same direction and have the same
wavelength.

Use 2 mirrors – one that is partially coated to produce
photons of light that have the same energy. When the
light has the right wavelength it is allowed to pass
through the holes in the coating on the second mirror.

Uses:

Read bar codes, read CD’s, surgery, cutting and welding,
surveying and leveling
Optical fibers

Total internal reflection occurs when light strikes
the surface between two materials and reflects
totally back into the first material.

Optical fibers transmit light from one end of the
fiber to the other.
Consist of a glass core surrounded by another
layer of glass and encased inside a plastic
coating.
 The light reflects within the core and can only exit
the ends.


Uses:
Communication – TV, telephone, computers
 Medical examinations and surgery


Advantages:
One fiber can carry thousands of phone
conversations
 Signals don’t leak or interfere with other
fibers.
