Chapter 11.1
• Types of Waves
• Vocabulary
terms: wave,
medium,
mechanical wave,
electromagnetic
wave, transverse
wave,
longitudinal wave
Flow of Energy, not Mass
Vibrations
Vibration or an oscillation - the motion of an object that
regularly repeats itself, back and forth, over the same
path.
Understanding Waves
• Transverse Waves - displacement is perpendicular to
the direction of motion of the wave
:
WAVES
Mechanical waves
Electromagnetic waves
Transverse waves Longitudinal waves Transverse waves
Longitudinal or Transverse?
Compression Waves
Sound Waves
Molecules in the air vibrate about some average position
creating the compressions and rarefactions. We call the
frequency of sound the pitch.
Electromagnetic Waves
Special Things About a
Light Wave
• It does not need a medium through which to travel
• Its highest velocity is the speed of light, c,
equal to 300,000 km/sec (or 3 X108 m/s)
• The frequency (or wavelength) of the wave determines
whether we call it radio, infrared, visible, ultraviolet,
X-ray or gamma-ray.
SURFACE WAVES
• SURFACE WAVES
The water drops go in
circles. Waves in the
ocean are an
example of surface
waves.
Rayleigh waves are surface waves
generated by earthquakes
Movement of water molecules:
Characteristics of
Waves
Vocabulary terms: crest,
trough, amplitude,
wavelength, period,
frequency, wave
speed, Doppler effect
Wave Speed
Wavelength is distance
between peaks
Frequency is number of
peaks per second going
past a point in the water
Frequency depends on
wavelength and how fast
the wave moves!!!
speed  wavelength  frequency
Wave Properties


Wavelength: The distance  between identical points on the wave.
Amplitude: The maximum displacement A of a point on the wave.
Wavelength

Amplitude A
A
PERIOD
• wave period :
• the time that elapses between the
passage of two successive wave crests
past a fixed point
• Ex. if frequency is 17, means 17 waves
passed in a second, so each wave has
• a period of 1/17 of that second.
Echolocation
Dolphins produce high frequency clicks. These sound waves bounce off objects
in the water and return to the dolphin in the form of an echo.
Chapter 11.3
•
WAVE INTERACTIONS
• Vocabulary terms: reflection, diffraction,
refraction, interference, constructive
interference, destructive interference,
standing wave.
•
•
•
•
•
Transmission of energy
Reflection
Refraction
Diffraction
Interference
Reflection of Waves
A travelling wave is reflected when it hits a barrier.
This phenomenon can easily be observed when a travelling water
wave hits a reflector in the ripple tank.
Reflector
Reflected
waves
Reflection
Wave Reflection
• Think of arrows pointing in the direction of
the wave motion
• We can trace the path of these arrows
Angles Equal
Wave Reflection
Acoustics of room design
is very interesting. Need
some reflections to
“liven” the room. Too
many reflections and the
sound gets mushy. Look
in a concert hall or
auditorium to see the
different sound treatments
Wave Refraction
Diffraction of Waves
When a travelling water wave hits an obstacle, the wave fronts
spreads out round the edge and becomes curved.
This phenomenon refers to diffraction.
The wavelength of the wave is not changed in diffraction.
Interference of Waves
When two or more waves propagating in the same medium meet at the
same point, interference is said to occur.
A stable interference pattern can be observed when two water
waves of same frequency meet one another in a ripple tank.
=
+
Interference
• Constructive
interference – the
waves combine into a
bigger wave.
• Destructive – one
wave subtracts – so
you get a smaller
wave.
Wave Interference
Wave Interference
Standing Waves
• Recall from the discussion of wave
interactions that waves can be reflected
when they encounter a boundary. When
that happens, the wave flips over and
heads back in the opposite direction. So
far, so good.
• Now suppose that a whole series of waves
are introduced into the medium. The
incoming waves will meet up with the
reflected waves. The result might be a
jumbled mess. But if the frequency of the
wave is just right, an interesting pattern
will emerge.
• Some points on the medium will move up
and down with very large amplitudes.
These are called ANTINODES. Other
points on the medium will not move at all.
These are called NODES. This pattern we
are describing is called a STANDING
WAVE
Standing Waves
• If a standing wave is established in a rope, and Frieda the fly were
sitting on a node, she would not feel the rope move. On the other
hand, her boyfriend Frankie the flea who's sitting on an antinode, will
be in for the ride of his life.
Guitar Strings