Waves
Energy is sometimes transferred
from place to place by traveling in
waves. Sound and light travel in
waves. Some substances
transport energy through them in
waves – like water waves.
A wave is an energy disturbance that
moves in a consistent manner. Some
waves can travel through a vacuum
(no matter), while others travel
through matter (called a medium).
Waves that pass through a medium
do so without causing permanent
movement of the medium.
There are different types of
waves with different types of
movement.
Ocean waves travel in transverse
waves. A transverse wave causes
particles to move up and down while
the wave moves forward
(perpendicular to the wave motion).
Light waves also travel in transverse
waves, however light waves are
electromagnetic waves.
Electromagnetic waves are able to
travel either through a vacuum or
within a medium.
The Electromagnetic Spectrum
Longitudinal waves (also called
compression waves) move particles
back and forth parallel to the wave
motion. Sound and earthquake
waves are longitudinal waves.
Waves have properties and
scientists use these
properties to describe
specific waves.
Transverse waves have crests and
troughs, a crest being the highest point of
displacement, and the trough the lowest
point of displacement. A node is the
point where it crosses the median line.
The wavelength of a transverse wave
is defined as the distance from one
crest (or top) of a wave to the next
crest on the same side.
The wavelength of a longitudinal
wave is measured from the center of
one compression to the
center of the next.
The frequency of a wave is the number of
wavelengths that pass a point in a second.
(You could count the frequency of ocean waves
by standing in one place on a dock and counting
how many wave crests pass in a given time
period.)
Frequency is usually measured in Hertz or
cycles per second.
The wavelength and frequency of the
same wave are related. As frequency
increases wavelength decreases and
as frequency decreases wavelength
increases. (Or you can say it the
other way . . . As wavelength
increases, frequency decreases, etc.).
The amplitude of a wave is
measure of the amount of
displacement it causes. In other
words, the amplitude is the
distance from the center of the
wave to it’s highest point.
Waves also interact with each other
in various ways.
Wave interference can occur
between waves. Interference can
increase wave amplitude if the crests
and troughs of the waves coincide. If
the crest and trough of two waves
coincide, they can cancel each other
or reduce the amplitude.
Waves can also be reflected when
they hit a surface.
SOUND
Sound travels in longitudinal waves.
Sound waves are made when an
object vibrates and causes
surrounding air molecules to take on a
compression wave motion. This
motion is picked up by our eardrums
and translated in our brains into
sounds.
Sound waves can only
travel in a medium (where
there is matter). They can
not travel in a vacuum.
Changes in wavelength of sound waves
cause volume changes, while changes in
frequency result in pitch changes.
Sound waves travel at a
speed of 330 m/s
in air at zero degrees Celsius.
Sound travels at different speeds in
different media (water, wood, etc.) and
at different temperatures.
LIGHT
Light waves are transverse.
Changes in wavelength
(and thus frequency)
cause light to appear in
different colors.
When white light waves (like sunlight)
pass through a prism the various
wavelengths are separated out into a
spectrum.
There are light wavelengths that are
visible and some that are invisible to
the human eye.
The visible spectrum includes red,
orange, yellow, green, blue, indigo,
and violet light.
When red, orange, yellow, green, blue,
and violet are combined, they produce
white light.
This entire visible spectrum can be
seen in rainbows, puddles with oil, as
light passes through water, etc.
Light waves travel in straight lines.
When light waves pass through a
small opening they cross each
other turning the image upside
down.
Light waves can be reflected.
Light waves can also be
refracted (bent).
When our eye looks at
the pencil in water, it
looks broken because
the light waves have
been bent by the
differing substances
(air is less dense than
water).
Speed of Light
The velocity of light waves
is consistent at
299,792,458 m /s.
Waves are constantly
surrounding us with light, sound,
and lots of other types of
energy!
Words to Remember
amplitude
trough
crest wavelength
frequency
pitch
electromagnetic spectrum
transverse wave
longitudinal wave
1. crest
2. trough
3. wavelength
4. node
5. amplitude
Which numbered term above goes with A
on the picture?
(Answer with a number 1-5.)
1. crest
2. trough
3. wavelength
4. node
5. amplitude
Which numbered term above goes with B
on the picture?
(Answer with a number 1-5.)
1. crest
2. trough
3. wavelength
4. node
5. amplitude
Which numbered term above goes with C
on the picture?
(Answer with a number 1-5.)
1. crest
2. trough
3. wavelength
4. node
5. amplitude
Which numbered term above goes with D
on the picture?
(Answer with a number 1-5.)
1. crest
2. trough
3. wavelength
4. node
5. amplitude
Which numbered term above goes with E
on the picture?
(Answer with a number 1-5.)
What is a wave?
A: traveling energy that causes a
temporary disturbance
B: permanent movement of a medium
C: energy that can only travel in a
vacuum
D: energy that can only travel through
matter
Which of the following is NOT
true? Sound waves
A: are compression waves.
B: are longitudinal waves.
C: must travel through a medium.
D: are transverse waves.
Transverse waves
A: have a series of compressions and
rarefactions.
B: move particles perpendicular to
direction of the wave.
C: have no amplitude.
D: must always travel through a
medium.
Electromagnetic waves are
unique because
A: they are the only type of transverse
waves.
B: they are the only type of
compression waves.
C: they can travel in a vacuum.
D: they require a medium in which to
travel.
Which is true of light waves?
A: they are transverse waves.
B: they are electromagnetic waves.
C: they can not travel in a vacuum.
D: A & C only
In longitudinal waves
A: particles move back in forth in motion parallel to
the wave motion.
B: particles move up and down in motion
perpendicular to the wave motion.
C: the particles in the medium are permanently
displaced when a wave passes through.
D: there is no temporary displacement of particles
as the wave moves through.
The frequency of a wave is
A: measure of the height of a wave.
B: the same as the wavelength.
C: the same as wave velocity.
D: the number of wavelengths that
pass a point in a given period of
time.
As the wavelength of a wave
increases
A: the frequency remains the
same.
B: the velocity increases.
C: the frequency decreases.
D: the frequency increases.
Some wavelengths of light are not
visible to the human eye.
A: True
B: False
Red light has a shorter
wavelength than violet light.
A: True
B: False
Yellow light, X-rays, microwaves,
and radio waves are all parts of
the electromagnetic spectrum.
A: True
B: False
Red, orange, yellow, green, blue, and
violet light wavelengths combine to
form
A: black light
B: the entire electromagnetic spectrum
C: white light
D: infrared light
Sound waves are affected by
temperature and density of the
medium they travel in.
A: True
B: False
Different colors of light have
different
A: crests
B: amplitudes
C: wavelengths
D: speeds
Changing the frequency of a sound
wave changes the
A: volume
B: amplitude
C: pitch
D: tone