Chapter 11 Waves

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Chapter 11 Waves

• Ever done the wave? Thats a transverse wave!

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11-1 Types of Waves

• Waves- a disturbance that transmits energy
  through matter or space.
• Mechanical waves- waves that require a medium
  (slower waves) --water waves, slinky waves, sound
  waves.
• Medium- matter through which a wave travels (the
  water of a water wave).
• Electromagnetic waves- a wave caused by disturbed
  electric and magnetic fields. Doesnt require a
  medium called light wave.

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• Waves carry energy. They do work on things.
• The medium vibrates, but particles dont really
  go anywhere, the energy does.
• Waves spread out in circles. Energy is more
  spread out as the circle increases. Sound gets
  quieter as you move away because energy has
  spread out and dissipated.
• Most waves are caused by vibrations (something
  rattling back and forth).

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• Wave vibrations represent movement of energy.
  Waves are transformations of energy elastic
  potential, kinetic, and gravitational potential
  energy conversions for example. (see p.359)
• These transformations run in a cycle like a
  pendulums motion, and repeat themselves as the
  energy moves through the medium.

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• This repeated motion is called simple harmonic
  motion.
• The tendency of a vibration to fade out as the
  next one starts is called damped harmonic motion.
• Compare Figs. 11-5 11-6note motion
  similarities.
• Particles in a wave vibrate (move up and down or
  back and forth, while the wave (and its energy)
  move forward.

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Transverse, Longitudinal and Surface Waves

• Transverse waves-particles of the medium vibrate
  perpendicular to the direction the wave is going.
• Ex. light waves, people doing the wave at a
  stadiumthey stand up and sit down, and the wave
  moves sideways to them.

Particles vibrate up and down...
while wave and its energy proceed forward in a
horizontal motion.
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longitudinal

• Longitudinal waves- causes particles to vibrate
  parallel to the direction the wave travels.
• Ex. Sound waves compress air in bands that move
  to your ears to be interpreted as the energy of
  sounds.
• Surface waves- combo of perpendicular and long.
  motion. Particles roll in a circular motion
  Ex. Beach ball in water.(p.364.

Compressed areas Rarefactions(Spread out areas)
Vibrating objects alternately compress and spread
out particles, sending wave.
Surface
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Intermission
Lets take a breakshall we?
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11-2 Characteristics of Waves

• Crest- highest point of a transverse wave.
• Trough-lowest point.
• Amplitude- how high or low the wave goes from the
  normal rest position.
• Larger waves (bigger amplitudes) carry more
  energy. In L-waves, this would mean intensity of
  compressions and rarefactions.
• Ex. Sound--Amplitude Volume or loudness.

amplitude
Crest
wavelength
Normal Rest Position
wavelength
trough
This general pattern of a sideways S - shape is
called a sine wave. Most transverse waves are
in this shape.
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• Wavelength-length of wave measured by distance
  between any 2 identical parts of wave.
• Period - how long it takes for waves to pass by
  (time).
• Frequency - number of vibrations or wavelengths
  per second. (How frequently the wave happens).
  In sound, freqpitch.
• Freq 1/period (in Hertz)

Time 1second
What is the frequency of this pattern? 3waveleng
ths/vibrations 1second thus, frequency 3
Hertz or period of this wave is (time for a
wave to pass) is 1/3 of a second (for each
wave)the inverse of the frequency.
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• Light comes in a variety of frequencies and
  wavelengths (see P.368, and spectrum handout).
  You are responsible for this information!
• These difference types are called, collectively,
  the electromagnetic spectrum.
• W.Speedfreq.Xwavelength
• Example If a piano string produces a frequency
  of 264Hz, and have a wavelength of 1.30m, what is
  the speed of this sound?
• V f X
• V 264Hz X 1.30m
• 343m/s for this waves speed.

Speed of a wave depends on the medium and
its temperature (density). In a given
medium/temp. the speed of a wave is constant.
Particles move more quick- ly back and forth if
they are bound together. Speed of light is a
definite number. 3 X 108m/s, or
186,000miles/second, a physics constant
often symbolized, c.
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Ultraviolet - above range of vision. (black
light) Range 7.5-50 Violet - range around 7.5
(limit of human vision) Indigo Range of
frequency (X 1014Hz) Blue Green range around
6.0 Yellow Orange range around 5.0 Red End
of visible spectrumrange around 4.3 Infrared -
below range of human vision (heat) range .003
to 4.3
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Doppler Effect
A
Observer A hears normally pitched horn sound.
Pitch is determined by frequency of a wave, or
how many waves/second come to observer.
C
B
Observer B hears a lower pitched sound, because
the movement of the car places more space between
each wave (leaving each wave a little further
behind. Observer C will hear a higher pitched
sound because the cars movement takes away a
little bit of the space between each wave. Ie.,
the car keeps up with each wave a little bit.
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11-3 Wave Interactions

• Reflection, Diffraction, Refraction
• Reflection- a wave bouncing back from a surface
  or boundary.
• At a free (moveable end) boundary, waves reflect.
  At a fixed (immovable) boundary, waves reflect
  and turn upside down.
• Diffraction - Waves bend around an edge or
  opening. (Waves bending around a log in water).

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• You see diffraction when you see a ripple bend
  around an object in water to fill the space
  behind it.
• Refraction - waves bend as they pass from one
  medium to another.
• You see this as bent lines of things or magnified
  images of things in a glass of water.
• Interference- when two or more waves are in the
  same place, they combine to make one wave. If
  crests and troughs line up with each other, they
  combine to make a larger wave (Constructive
  interference). If they are out-of-step, they
  tend to cancel each other out and get smaller
  (two identical and opposing waves cancel to
  zero)this is called Destructive interference.
  See examples on page 377.

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• Interference patterns in light waves create color
  patterns. The waves of some light colors pass
  through the shell of the bubble and
  constructively or destructively interfere to
  create patterns (see right)
• Sound waves that are similar but not the same in
  freq. interfere Con./Dest. to create beats or
  series of loud and soft sounds. Piano tuners use
  this to tune the piano to the exact frequency
  that is right.

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• Standing waves - repeated waves of the same
  frequency will interfere with each other and
  create standing waves. These are waves that
  appear not to move.
• The waves have regions of no vibration (nodes)
  and regions of maximum vibration (antinodes).
• St.waves occur where the wavelength is a precise
  multiple of the length of the string.
• These waves are common in instruments (string,
  wind, etc.). Fundamental frequencies are the
  full 1/2 wave vibration, and the overtones
  characteristic of that instrument are smaller
  standing waves (see examples, p.380).

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THE END