Chapter 23
Characteristics of Waves
23-1 Nature of Waves
• Ocean waves don’t flood
the beach because they
don’t carry water—they
only move it up and down,
not forward.
• Waves are formed along
the surface of the water as
the result of a disturbance.
• Waves carry energy.
• A wave is a traveling disturbance that
carries energy from one place to another.
• Waves get their energy from vibrations
caused by something that is moving.
• Electric charges can vibrate to create light
and microwaves.
• The matter that energy
travels through is called a
medium.
• Mechanical waves require
a medium to carry energy
while electromagnetic
waves do not.
• Mechanical wave = sound
• Electromagnetic = light.
23-2 Characteristics of Waves
• All waves have
amplitude,
wavelength, and
frequency.
• The highest point of a
wave is the crest.
• The lowest point of a
wave is the trough.
Amplitude
• A wave’s maximum
movement from rest is
called amplitude.
• It’s the distance from rest
to the crest or trough.
• The higher the amplitude
the greater the energy.
Wavelength
• The wavelength is the
distance from crest to crest
or trough to trough.
• Longer wavelengths have
less energy than short
ones.
• The symbol for
wavelength is the Greek
symbol lambda λ.
Frequency
• The number of complete
waves per unit of time is
frequency. It is usually
measured in waves per
second.
• The unit used to measure
frequency is the hertz
(Hz).
23-3 Types of Waves
• Depending on the
motion of the
medium as
compared to the
movement of the
wave, waves are
classified as either
transverse or
longitudinal.
Transverse Waves
• Transverse waves are
the same type as a
wave on a rope.
• A wave in which the
motion of the medium is
at right angles to the
direction of the wave is
called a transverse
wave.
• Light and other
electromagnetic waves
are transverse waves.
Longitudinal Waves
• Longitudinal waves have a series of compacted particles
(compression) and spaces of uncompacted particles
(rarefaction).
• The motion of the medium is parallel to the direction of the
wave.
• These waves move like a slinky.
Combinations of Waves
• Some waves are a
combination of transverse
and longitudinal waves.
• An example is a surface
wave which occur at the
surface between the two
mediums.
• Water waves are surface
waves because they travel
between water and air. The
particles move up and down
and back and forth.
23-4 Speed of Waves
• The speed of a wave depends on the number of
waves passing a point in a certain amount of time.
• Speed = frequency x wavelength
• Speed = f x λ
• In a given medium, the speed of a wave is constant.
• The speed of a wave depends upon the medium
through which it is traveling.
• The more dense a medium is, the slower the wave
will travel through it because the denser medium has
more inertia.
• A wave moves faster through a medium that is
elastic. Elasticity is the ability of the medium to return
quickly to its original shape after being disturbed.
23-5 Interactions of Waves
• When a wave is traveling through a
medium and hits a different medium,
like air to water, it will either be
reflected, refracted, diffracted or
encounter interference.
Reflection
• If a wave hits a barrier, at
least part of it will bounce
back. This is reflection.
• The law of reflection states
that the angle of incidence (i)
is equal to the angle of
reflection (r).
• Looking in the mirror is an
example of light waves
reflecting back with your
image.
Refraction
Bent looking straw due to refraction
• When waves go
from one medium to
another and the
speed of the wave
changes, the waves
will bend as they
either speed up or
slow down. This is
refraction.
Diffraction
• The bending of
waves around the
edge of an obstacle
is diffraction.
• The amount of
diffraction depends
on the wavelength
and the size of the
obstacle.
Interference
• When two or more
waves arrive at the
same place at the
same time, that’s
interference.
• There are two kinds:
constructive and
destructive.
Constructive Interference
• Constructive interference
occurs when waves with
different amplitudes line up
together—crests and
troughs.
• The crests of the two waves
add together to form a single
wave with an amplitude
equal to the sum of the
amplitudes of the two
original waves.
Destructive Interference
• With destructive
interference, the crests
don’t line up and the
amplitudes subtract one
another out.
• If the crest of one wave
occurs at the trough of
another wave, they will
cancel one another out
with no wave at all.
Standing Waves
• If a wave vibrates at
just the right
frequency, it will
appear to stop
moving and create a
standing wave.
Standing Waves
• Standing waves result
when an object vibrates
at its resonant
frequency and multiples
of that frequency. The
top wave has two nodes
and one antinode.
What about the others?
Resonance
• An object that is
vibrating at its
natural frequency
can cause another
object to vibrate by
absorbing energy of
its own natural
frequency. This is
called resonance.
Tacoma Narrows Bridge
1940