1' Definition

1
1. Definition
WAVES ARE AN OSCILLATING DISTURBANCE PROPAGATING
IN SPACE WAVES TRANSFER ENERGY
Examples sending a message, fans making a wave
at a stadium, light, music, speech, ocean waves
2
2. Types of Waves

• Mechanical Waves
• Require a medium to travel through (eg air,
  water, earth, string)
• Caused by vibration of an object that disturbs
  the medium
• Can be transverse or longitudinal
• Electromagnetic Waves
• Transfer energy through a vacuum
• Caused by vibration of electrons or charges
• Transverse only

3
Electromagnetic Waves

• Also called light waves --- not just visible
  light!!!
• Accelerating/oscillating charge generates a
  changing E-field and a changing B-field
• Changing fields can be conceptualized as
  transverse waves oscillating at right angles to
  one another.
• James Clerk Maxwell derived a wave form of
  electric and magnetic equations to explain the
  wave nature of these fields.

4
(No Transcript)
5
Electromagnetic Spectrum
6
2. Types of Waves - Motion
Transverse oscillations perpendicular to the
direction of propagation
Longitudinal oscillations parallel to the
direction of propagation
Rarefaction
7
2. Types of Waves - Motion

• Oscillation
• vibration
• back and forth motion of individual particles as
  they remain in one location
• describes the motion of matter
• Propagation
• wave motion
• transfer of energy through the medium or vacuum
  by successive particle vibrations
• describes the motion of the wave and the transfer
  of energy

8
2. Types of Waves Combination Transverse and
longitudinal components
9
2. Types of Waves - Duration
a. Pulses
Pulse a short disturbance propagating in space
10
2. Types of Waves
b. Periodic waves
Periodic Waves continuous periodic oscillation
driven by a periodic driving force
Wavelength
Crest
Trough
11
3. Wave Anatomy
Amplitude (A) amount of particle vibration
greatest distance the particles move from rest
points Wavelength (?) distance between two
equivalent parts Crest highest portion portion
of a wave Trough lowest portion of a wave
12
Longitudinal Wave Anatomy
Rarefaction Medium is in a relaxed state.
Particles are apart. Compression Medium is in a
condensed or compressed state. Particles are
close together. Sound waves are longitudinal
waves. Compression and rarefaction of the air
transfers energy from source to observer.
How do you graph rarefaction and compression? Use
the sine curve to represent DENSITY rather than
amplitude.
13
3. Characteristics of Periodic Waves

• Frequency (f)
• How often a vibration occurs
• of waves or oscillations passing a point in
  space in a given time interval
• oscillations per second
• Units hertz (Hz), cycles per second (s-1)
• Period (T)
• Time needed to create a single vibration
• Units seconds (s)
• Frequency and period are inverses
• f 1/T T 1/f
• Wavelength (?)
• distance between two equivalent parts of a wave
• Units meters (m)

14
4. Universal Wave Equation
v wave speed (m/s) f frequency (Hz) l
wavelength (m)

• Wave speed depends on the medium
• Sound waves travel fastest in a solid, then
  liquid, then gas
• Waves travel as fast as they can disturb the next
  particle (solid particles are closer together)
• Light has a finite speed in a vacuum 3.0 x 108
  m/s.
• It is slowed down slightly by water, air, or
  other matter.

15
5. Wave Properties

• Reflection

Free Boundary
Fixed Boundary
16
5. Wave Properties
a. Reflection
Law of Reflection Angle of incidence equals
angle of reflection
17
5. Wave Properties
b. Refraction
When light passes through a denser material, it
slows down and bends! When light passes into a
less dense material, it speeds up and bends!
18
5. Wave Properties
c. Superposition addition of two waves in the
same place at the same time the effect of this
addition is called interference
Waves converge and are momentarily on top of
each other. If the crests converge you get
constructive interference If a crest and trough
converge, you get destructive interference
19
5. Wave Properties
c. Interference
20
Superposition
21
Standing Waves

• Superposition of two waves of equal amplitude,
  frequency, and wavelength traveling in opposite
  directions

22
Beats

• Two waves of equal amplitude and speed, but
  different frequency and wavelength traveling in
  the same direction

23
Resonance

• Everything has a natural frequency that it wants
  to vibrate at.
• Strike a glass with your spoon, and vibrates at a
  certain frequency. No matter how many different
  ways you strike the glass, it always sounds the
  same.
• Apply a forced vibration on an object, and it
  will vibrate at that frequency. If the forced
  vibration matches the natural frequency of the
  object, the object can literally shake itself
  apart.
• Tacoma Narrows Bridge, shattering a glass with
  your voice, soldiers crossing a foot bridge.

24
Doppler Effect
When an object approaches, the sound it emits
seems to have a higher pitch (frequency) than it
really does
Fig 11.50, p.407
Slide 24
25
Doppler Effect
When an object recedes, the sound it emits seems
to have a lower pitch (frequency) than it really
does
Fig 11.50, p.407
Slide 25
26
Doppler Effect

• Pitch is determined by the frequency of sound
  waves
• Frequency changes when the source of the waves is
  moving.
• You hear a higher pitch when the source is moving
  toward you.
• You hear a lower pitch when the source is moving
  away from you.

Pitch is determined by the frequency of the sound
waves Frequency changes when the source of the
waves is moving
27
Doppler Effect

• Stationary Source

• Moving Source (v lt vs)

28
Doppler Effect How is this Useful?

• Radar Guns
• catching speeders
• timing baseball pitches
• Red Shift
• Edwin Hubble (1929) observed hydrogen spectra
  from distant galaxies. Noticed a shift from
  hydrogen spectrum on earth.
• Concluded that source of light (distant galaxies)
  were moving away from us
• Evidence for Expanding Universe theory
• Put this information in REWIND ?we begin with a
  very small universe

29
Red Shift
This is hydrogen spectrum here On earth
Small shift Far away
Large shift VERY far away
30
Sound Properties Sonic Boom

• Travel faster than the speed of sound
• Hear nothing in front of the plane
• Depending on position, hear the boom or just the
  plane, behind the plane.

31
Doppler Effect Sonic Boom

• Moving Source (v vs)

• Moving Source (v gt vs)