CH 8
Waves
A
WAVE is:
a disturbance that transmits energy through
matter or space in a regular pattern.
Most waves are caused by…
vibrating matter or particles.
A medium is: the matter
through which a wave
travels; i.e. water, air
Two types of waves, mechanical and
electromagnetic.
MECHANICAL WAVES
• Require a medium!!
• 2 types - Longitudinal or transverse
•Examples:
Longitudinal: sound, spring waves
Transverse: water waves, some
seismic
waves
Turn the page and forget about Electromagnetic waves, we will get back to them.
Longitudinal (compressional)
  particle motion  
  wave motion  
Particle Movement and Parts of a
Longitudinal wave
Particles in the medium move parallel
to the direction of the waves.
The dense areas are called
compressions.
The less dense areas are rarefactions.
Wavelength is measuring from
compression to compression or
rarefaction to rarefaction
Longitudinal Waves
• https://www.youtube.com/watch?v=7cDAY
FTXq3E
Parts of a Transverse
Wave
crest
wavelength
amplitude
trough
Transverse
Particles in the medium move perpendicular
to the direction of the waves.
wave motion
particle
motion
Parts of a Wave
• Crest: the highest point (top) of a
transverse wave.
• Trough: the lowest point (bottom) of a
transverse wave.
• Wavelength: the distance from any point on
a wave to the same point on the next wave.
(ex: crest to crest)
• Amplitude: the height measured from the
resting position.
Motion of a Duck on a Wave
Water Wave
Seismic waves are transverse.
ELECTROMAGNETIC WAVES
(Turn back to page 1 to Complete the chart)
• Do not require a medium!! (Can travel
in a vacuum like outer space.)
•7 types of Electromagnetic Wavesradio waves, microwaves, infrared
rays, visible light,
ultraviolet, x-rays,
gamma rays
•Modeled as transverse motion.
(So they travel like ocean waves.)
Electromagnetic Waves
Return back to the bottom of page 2
ELECTROMAGNETIC WAVES
Electromagnetic waves do not require a _______________________.
Electromagnetic waves travel as ______________________.
Listed in order from least energy to most-___________________________________________________
8.2 Wave Properties and
Measurements
AMPLITUDE
Not only is it the height of a wave but
it measures the amount of
energy in a wave.
Greater amplitude = more energy.
WAVELENGTH
Symbol: Greek letter lambda, λ
Tool: meterstick
Unit: meter (m)
PERIOD
Time it takes for a full wavelength to pass.
Symbol: T
Tool: stopwatch
Unit: seconds (s)
FREQUENCY
The rate at which waves pass (the
# of full wavelengths that pass a
point in 1 second).
Symbol: f
Unit: Hertz (Hz)
1 Hertz = 1 vibration per second
Frequency is the inverse period
1/P
WAVE SPEED
How fast a wave moves.
Symbol: v
Unit: m/s
Wave speed is determined by the
medium. Generally, waves pass
through solids faster b/c particles
are closer and can pass vibrations
to each other more quickly.
WAVE SPEED cont.
EX: Speed of sound in air: 340 m/s
in water: 1490 m/s
in iron: 5000 m/s
An exception is light, which travels
slower in a medium than in empty
space (vacuum).
All electromagnetic waves travel at a
speed of 3.0 x 108 m/s (186,000
mi/s) in a vacuum.
Sound Waves
• https://www.youtube.com/watch?v=Ude8pP
jawKI
EQUATIONS
Wave speed = frequency times wavelength
v=f·λ
f=v/λ
λ=v/f
UNITS: λ = meters (m)
f = Hertz (Hz)
v = m/s
v
f
λ
The string of a piano that produces the note
middle C vibrates with a frequency of 264 Hz. If
the sound waves produces have a wavelength of
1.30 m in air, what is the speed of sound in air?
Data
Formula
Work
Ans
A water wave has a speed of 1.3 m/s. A person
sitting on a pier observes that it takes 1.2 s for a
full wavelength to pass the edge of the pier. What
is the wavelength of the water wave?
Data
Formula
Work
Ans
8.3 Wave Behavior
• All electromagnetic waves travel at the
speed of light in empty space.
C = 3.0 X 108 m/s (186,000mi/s)
Light travels slower through a medium.
The Doppler Effect
An observed change in the frequency of a wave
when the source or observer is moving.
The sound waves’ frequency and pitch are higher
as the ambulance moves toward A.
The sound waves’ frequency and pitch are lower
as the ambulance moves away from the observer.
Closer waves = high frequency, high pitch
Frequency and Pitch are directly related.
DOPPLER EFFECT
Pitch of a sound is determined
by the wave’s frequency
https://youtu.be/z0EaoilzgGE
Auto Racing
•
•
Sound waves from an approaching object are
closer together than sound waves from the
object when it is standing still. The speed of
the approaching object determines how much
closer the waves will be. The sound waves
from an object going away are farther apart
than the waves from the same object standing
still. Again the speed of the object determines how much farther apart the waves
from the moving object are than those from
the stationary object.
A race fan standing by the track hears a
high-pitched sound as a car approaches
which changes suddenly to a lower pitch as
the car passes and begins to move away. The
amount of change in pitch is determined by
the speed of the car. Fans with perfect pitch
can clock a car reasonably accurately by
listening to the pitch change in the sound of
the engine as the car passes them.
Reflection
•The bouncing back of a wave
as it meets a surface or
boundary
Reflection
•When a wave has a free boundary they reflect
like the original wave
•When a wave has a fixed boundary they reflect
upside down
Free boundary
Fixed boundary
Diffraction
•The bending of a wave
as it passes an edge or an
opening
Diffraction
Refraction
•The bending of waves as they
pass from one medium to another
Refraction
•Each time a wave enters a
new medium they bend
Refraction is the bending of a wave
when it enters a medium where it's
speed is different.
Refraction is
responsible for
image formation
by lenses and the
eye.
Types of Interference
•
•
•
•
Constructive
Destructive
Light wave interference
Sound wave interference
Constructive Interference
• When the crest of one wave overlaps the
crest of another wave resulting in a new
wave with an amplitude that is the sum
(larger) of the 2 individual waves
amplitudes.
• Resulting amplitude is larger.
Destructive Interference
• When the crest of one wave overlaps the
trough of another and the resulting wave’s
amplitude is smaller than the original 2
wave’s amplitudes.
Light Interference
Iridescence of
peacock feathers is
caused by
light reflected from
complex layered
surface
Sound Interference – Interference of
sound waves produce BEATS
White Noise?????
• Because white noise contains all
frequencies, it is frequently used to mask
other sounds.
– Example: If you are in a hotel and voices from
the room next-door are leaking into your room,
you might turn on a fan to drown out the
voices.