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Wave Phenomena

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Wave Phenomena Characteristics of Waves * * * What is a wave? A wave is a vibratory disturbance through a material (medium) or space Waves transfer ENERGY without ... – PowerPoint PPT presentation

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Title: Wave Phenomena


1
Wave Phenomena
  • Characteristics of Waves

2
What is a wave?
  • A wave is a vibratory disturbance through a
    material (medium) or space
  • Waves transfer ENERGY without transferring mass

3
Classifying Waves1. Electromagnetic waves
  • No medium required
  • Travel at the speed of light
  • c 3 x 108 m/s
  • Examples visible light, x-rays, infrared
  • Reference Table Electromagnetic spectrum

4
2. Mechanical Waves
Require a medium ex. Sound, water, waves in
springs
  • A. Longitudinal waves - vibrate parallel to wave
    motion
  • Examples - sound, seismic s-waves
  • B. Transverse waves - vibrate perpendicular to
    wave motion
  • Examples light, seismic p-waves, water

5
Transverse or longitudinal?
Longitudinal
Transverse
6
(No Transcript)
7
  • What is a pulse? How can we describe its motion?

A pulse is a single vibration moving at constant
speed
Pulse Periodic wave
8
Important
  • Speed of a wave or pulse doesnt change unless
    the characteristics of the medium change

9
Periodic Waves
  • Sketch

10
  • frequency (f)

number of vibrations per unit time units hertz
(1 hertz 1 cycle per second)
period (T)
time required for 1 vibration units
seconds equation
11
  • wavelength (?)

distance between two points in phase units meters
12
phase
  • points on wave having the same displacement from
    rest position AND moving in the same direction
    (up or down only) are in phase

Examples A E I, B F, C G, D H
13
speed
?
?
units m/s
14
amplitude
maximum displacement of a particle from rest
position
15
  • Examples

? f T



6 m
2 Hz
.5 s
3 m
4 Hz
.25 s
2 m
.17 s
6 Hz
L 3m v 12 m/s
T1/f
v f ?
16
Relationship between T, f and ?
  • As frequency increases (at constant velocity),
    what happens to wavelength?
  • decreases
  • As frequency increases, what happens to period?
  • decreases

17
Doppler Effect
  • Change in apparent frequency caused by
    relative motion between a source and an observer

Object moving toward you shorter ? higher f
Object moving away from you longer ? lower f
18
Examples
  • 1. Sound - train whistle - higher pitch as it
    moves toward you, lower pitch as it moves away.
  • 2. Light - Red Shift Evidence of Big Bang
    Theory - as universe expands, stars move away,
    larger wavelength and smaller frequency - shift
    toward red end of spectrum

19
(No Transcript)
20
What is a wave front?
Adjacent points on a wave that are in phase with
each other
Point source Line source
21
  • Wave fronts for a moving object

Point source - stationary
Point source -moving
22
What happens to a wave when a new medium is
encountered?
  • Frequency from the source is constant
  • Since v f?, if velocity changes, then
    wavelength changes
  • Wave can be reflected, transmitted through a new
    medium, or absorbed by the new medium

23
How can we describe wave interference?
  • Two or more waves pass through the same region -
    original wave is unchanged

24
  • Constructive interference- two crests meet, or
    two troughs meet
  • Maximum when phase difference is 0 or 360 (360
    is a whole wave)
  • Destructive interference - crest meets trough
  • Maximum when phase difference is 180 (180 is
    half of a wave)

25
Constructive or Destructive?
Destructive - 180 out of phase
26
Constructive or Destructive?
Constructive - 0 or 360 (in phase)
27
Constructive or Destructive?
Both constructive and destructive
28
Law of Superposition
  • Resultant displacement is the algebraic sum of
    the displacements due to the individual waves

29
The red wave is the resultant wave.
30
  • What will the resultant wave look like?

31
What are standing waves
  • Two waves of the same frequency and amplitude
    moving in opposite directions

Nodes - points that appear fixed Antinodes
(modes) - points of maximum amplitude above and
below rest position
32
Sketches
? L




2L
?/2
L
?
2/3 L
3/2 ?
L/2
2?
How are the number of nodes related to the number
of antinodes?
N A 1
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