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Physics 211 lecture 26: Wave Motion

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Examples: radio, TV, X-ray, gamma ray, microwave, all other EM waves. Two ways waves propagate: ... y = (0.25m) sin(0.3x 40t) with x,y in meters and t in ... – PowerPoint PPT presentation

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Title: Physics 211 lecture 26: Wave Motion


1
Physics 211 lecture 26 Wave Motion
  •  
  • Waves consist of disturbances that propagate
    through a substance or region of space.
  • Waves typically consist of either a single
    disturbance (wave pulse) or a series of
    disturbances one after another (periodic wave).
  • Two types of waves
  •             Mechanical    - travel through
    matter                                    -
    observed as a disturbance in matter
  •                        Examples earthquakes,
    sound, water waves, strings, slinky,
  •             Electromagnetic     - travel through
    matter or empty space                            
                     - observed as a disturbance in
    electric and magnetic fields
  •                        Examples radio, TV,
    X-ray, gamma ray, microwave, all other EM waves
  •  
  • Two ways waves propagate
  •             Longitudinal Waves - disturbances
    move parallel to direction of wave
  •                     Examples sound, lines at
    stadiums,
  •             Transverse Waves - disturbances move
    perpendicular to direction of wave
  •                     Examples EM waves, water
    waves (mostly), stadium wave cheer,

2
Wave Properties
  • wavelength (  ?  ) - length between
    two similar points on a wave
  • angular wave number (  k  ) - amount of wave
    angle fitting in a unit of distance
  • period (  T  ) - time for one full
    wavelength to pass by a fixed point
  • frequency (  f  ) - number of
    wavelengths passing by per unit of time
  • angular frequency (  ?  ) - amount of wave
    angle passing by per unit of time
  • amplitude (  A  )- maximum movement
    from disturbance by wave

Diagram Team task Draw a wave and label as
many properties as you can
Wave Equations
3
Example (Waves) Find wavelength for X-ray with
f1018Hz in tissue and in air.
Given                    Path                  
Want           Conversions/Equations
Example (Waves) Find speed of ocean wave w/
period 15s and wavelength 25m.
Given                    Path                  
Want           Conversions/Equations
4
Wave Behavior at an Interface
  • Reflection portion of wave changes direction to
    avoid entering a new medium at an interface
  • Inverted wave rebounds with same displacement
    as arrival
  • Non-inverted wave rebounds with negative
    displacement of arrival
  • Transmission portion of wave continues at
    reduced energy into a new medium through an
    interface
  • Diagrams Team task draw and label
  • 1) an inverted reflection 2) a non-inverted
    reflection 3) transmission

5
Wave Equations
  • The wave function assume wave travels in
    x-direction as a function of time

Displacement of wave with time due to wave
propagation
Height of wave above or below equilibrium
Position at which you observe the wave
The sinusoidal wave function
Diagram
Substitute in to write in terms of angular wave
number and angular frequency
To see how the wave moves visit http//www.silcom
.com/aludwig/images/snake.gif
Note if timing of wave does not start at y0,
then must add in phase constant ? to sine term
6
  • Example Ch 16 2
  • Ocean waves with crest-to-crest distance of 10m
    can be described by the wave function y(x,t)
    (0.8m) sin0.628(x - vt) where v1.2m/s.
  • Sketch y(x,t) at t0s
  • Sketch y(x,t) at t2s
  • How far did the wave shift during this time?

7
  • Example Ch 16 13
  • A sinusoidal waves is described by
  • y (0.25m) sin(0.3x 40t) with x,y in meters
    and t in seconds. Find the
  • amplitude
  • angular frequency
  • angular wave number
  • wavelength
  • wave speed
  • direction of motion

8
Questions for Groups
  • 16.6 If you shake one end of a taut rope
    steadily three times per second, what would the
    period of the sinusoidal wave set up in the rope?
  • 16.16 Earthquakes create both S (longitudinal at
    about 5km/s) and P (transverse at about 8km/s)
    waves that emanate from the focus. By detecting
    the arrival time of the waves, how can one
    determine the distance to the focus? Also, how
    many stations are needed to locate the focus
    unambiguously?
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